**Weed Control by Organic Mulch in Organic Farming System**

Rita Pupalienė, Aušra Sinkevičienė, Darija Jodaugienė and Kristina Bajorienė

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/60120

#### **1. Introduction**

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64 Weed Biology and Control

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Weeds are one of the most significant agronomic problems in organic farming [1] and they are an important factor limiting the spreading of organic farming system in the world [2]. Mulching reduces weed incidence in crops [3–7] and is increasingly used as a weed control measure, which is of special relevance in an organic cropping system when growing high quality and safe plant raw materials for food production [8]. Mulching of plant residues is applied in agricultural crop production and exerts many-sided effects on the agroecosystem [9]. [4], [6], [10], estimated that mulches (straw, grass and others) provide weed control. Mulches can control weeds by several ways: as physical barrier and by associated changes in the microclimate, pH, C:N ratio of the soil, immobilization of nutrients, inhibition by allelopatic compounds, less amount of visible light reaching the soil surface. Organic mulches maintain a more stable soil temperature and optimal moisture content, which results in more favourable conditions for living organisms' activity in the soil [11]. Organic mulches enhance soil enzyme activity [12, 13], amount and diversity of soil biota [14–16]. Soil biological properties largely determine crop productivity in organic farming system. Mulching often is used for the influence on soil physical properties. Mulching helps to reduce moisture evaporation from the soil, diminish and maintain a more constant soil temperature [17–19], and this is also very important for the crop growth and yield. Natural organic mulch eventually breaks down and adds organic material back into the soil. Slow nutrient release during mulch decomposition process is more synchronized with plant needs [20, 21]. It was found that straw mulch [22] and grass mulch [23] tended to increase available phosphorus and potassium contents in the soil. Quickly decomposing organic mulch serves as an important source of nutrients for plants. Significantly higher crop yields were obtained in grass mulched plots not only due to weed

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smothering but due to higher plant nutrient content in the soil and better soil physical properties [24]. Better growing plants have higher ability to suppress weeds.

Some research evidence suggests that mulching reduces the occurrence of annual weeds; however, it does not exert any effect on perennial weeds [25–27]. Plant residues (straw and others) used as mulch have been found to suppress weed emergence and growth due to the phytotoxins released during the breakdown process [28–30]. Many authors [25, 26, 31] observed a reduction in the number of annual weeds using crop residues for soil mulching. A reduction of weed density was established as the level of soil cover increased [3]. Mulching reduces soil bulk density and shear strength and increases air filled porosity [32–34]. The growth of some perennial weeds depends on those soil properties [35].

Some organic mulches are good for using in large scale farms –over-ground mass of catch crops, peat, sawdust, straw and other residues of agricultural crops. In small scale farms and gardens we can use still varied organic residues for mulching: grass regularly cut from grassplots, hulls of sunflower seeds, nuts, coffee beans and others.

The aim of the investigation was to evaluate the influence and the residual effect of different organic mulches and different thickness of mulch layer on weed emergence.

### **2. The investigation of organic mulches for weed control**

The two factor stationary field experiment was carried out at the Experimental Station of Aleksandras Stulginskis University (previously Lithuanian University of Agriculture) (54°53'N, 23°50'E). The soil type – *Calc(ar)i – Endohypogleyic Luvisol.* The influence of organic mulches and different thickness of mulch layer on weed density was investigated in 2004– 2009, in 2010–2012 the residual effect of the mulches and mulch layer was studied. Treatments of the experiment: Factor A – mulch: 1) without mulch; 2) straw mulch (chopped wheat straw); 3) peat mulch (medium decomposed fen peat); 4) sawdust mulch (from various tree species); 5) grass mulch (regularly cut from grass-plots). Factor B – thickness of mulch layer: 1) 5 cm; 2) 10 cm.

Randomised design was used (Fig.1.). Individual plot size was 2 x 6 m. The experiment involved 4 replications.

In 2004 in each plot common bean *Phaseolus vulgaris* L. cultivar *Baltija,* 2005 – common onion *Allium cepa* L. cultivar *Stuttgarter Riesen*, 2006 *–* red beet *Beta vulgaries* subsp. *vulgaris* convar. *vulgaris* var. *vulgaris* L. cultivar *Cylindra*, 2007 – white cabbage *Brassica oleracea* var. *capitata* f. *alba* L. cultivar *Kamennaja golovka* in raws with interlinears 0.5 m, 2008 – potatoes *Solanum tuberosum* L. cultivar *Anabela* in raws with interlinears 0.7 m, in – 2009 – *Phaseolus vulgaris* L. cultivar *Igoloneska* in raws with interlinears 0.5 m were grown. In 2010, common onion *Allium cepa* L. cultivar *Stuttgarter Riesen*, in 2011 – red beet *Beta vulgaris* subsp. *vulgaris* convar. *vulgaris* var. *vulgaris* cultivar *Kamuoliai,* and in 2012 – white cabbage *Brassica oleracea* var. *capitata* f. *alba* L. cultivar *Kamennaja golovka* was grown.

**Figure 1.** Field experiment

smothering but due to higher plant nutrient content in the soil and better soil physical

Some research evidence suggests that mulching reduces the occurrence of annual weeds; however, it does not exert any effect on perennial weeds [25–27]. Plant residues (straw and others) used as mulch have been found to suppress weed emergence and growth due to the phytotoxins released during the breakdown process [28–30]. Many authors [25, 26, 31] observed a reduction in the number of annual weeds using crop residues for soil mulching. A reduction of weed density was established as the level of soil cover increased [3]. Mulching reduces soil bulk density and shear strength and increases air filled porosity [32–34]. The

Some organic mulches are good for using in large scale farms –over-ground mass of catch crops, peat, sawdust, straw and other residues of agricultural crops. In small scale farms and gardens we can use still varied organic residues for mulching: grass regularly cut from grass-

The aim of the investigation was to evaluate the influence and the residual effect of different

The two factor stationary field experiment was carried out at the Experimental Station of Aleksandras Stulginskis University (previously Lithuanian University of Agriculture) (54°53'N, 23°50'E). The soil type – *Calc(ar)i – Endohypogleyic Luvisol.* The influence of organic mulches and different thickness of mulch layer on weed density was investigated in 2004– 2009, in 2010–2012 the residual effect of the mulches and mulch layer was studied. Treatments of the experiment: Factor A – mulch: 1) without mulch; 2) straw mulch (chopped wheat straw); 3) peat mulch (medium decomposed fen peat); 4) sawdust mulch (from various tree species); 5) grass mulch (regularly cut from grass-plots). Factor B – thickness

Randomised design was used (Fig.1.). Individual plot size was 2 x 6 m. The experiment

In 2004 in each plot common bean *Phaseolus vulgaris* L. cultivar *Baltija,* 2005 – common onion *Allium cepa* L. cultivar *Stuttgarter Riesen*, 2006 *–* red beet *Beta vulgaries* subsp. *vulgaris* convar. *vulgaris* var. *vulgaris* L. cultivar *Cylindra*, 2007 – white cabbage *Brassica oleracea* var. *capitata* f. *alba* L. cultivar *Kamennaja golovka* in raws with interlinears 0.5 m, 2008 – potatoes *Solanum tuberosum* L. cultivar *Anabela* in raws with interlinears 0.7 m, in – 2009 – *Phaseolus vulgaris* L. cultivar *Igoloneska* in raws with interlinears 0.5 m were grown. In 2010, common onion *Allium cepa* L. cultivar *Stuttgarter Riesen*, in 2011 – red beet *Beta vulgaris* subsp. *vulgaris* convar. *vulgaris* var. *vulgaris* cultivar *Kamuoliai,* and in 2012 – white cabbage *Brassica oleracea* var. *capitata* f. *alba*

properties [24]. Better growing plants have higher ability to suppress weeds.

growth of some perennial weeds depends on those soil properties [35].

organic mulches and different thickness of mulch layer on weed emergence.

**2. The investigation of organic mulches for weed control**

plots, hulls of sunflower seeds, nuts, coffee beans and others.

of mulch layer: 1) 5 cm; 2) 10 cm.

L. cultivar *Kamennaja golovka* was grown.

involved 4 replications.

66 Weed Biology and Control

In 2004–2009 mulch was spread manually in a 5 cm and 10 cm thick layer shortly after sowing (planting). Remains of mulch were inserted into the soil by ploughing. The soil was ploughed after crop harvest in the autumn. In 2010—2012 in all experimental plots crops were grown without mulch, the residual effect of organic mulches was investigated. During all period of experiment the crops were grown employing common organic crop production technologies. The plots without mulching were weeded 2–3 times per vegetation. No chemical plant protection products and fertilizers were used when investigating the influence and residual effects of mulches. The C:N ratio in the mulches used was as follows: in straw 51:1; in peat 40:1; in sawdust 133:1; in grass 11:1.

Weed emergence dynamics. Weed seedlings were counted in each plot in four permanent 0.2 × 0.5 m sites. Assessments were done every 10 days from May to October. During each assessment, the weeds were pulled out, counted and their species composition was deter‐ mined. The number of weeds was re-calculated into weeds m-2.

Number of weed seeds in the soil. Soil samples were taken by a sampling auger from the 0-25 cm layer after harvesting of agricultural crops. The number of weed seeds was determined by [36] method. The number of weed seeds found in the arable layer (0-25 cm) was re-calculated into thousand seeds m-2.

The means were compared using Fisher's protected LSD test at *P*(level) <0.05 with ANOVA procedure with SYSTAT 10 [37]. Data transformations lg(x+1) were used as necessary to achieve statistical normality [38]. Pearson's correlation coefficient was used to evaluate the relationships between indices. Probability level: \*– 95 %, \*\* – 99 %, \*\*\* – 99.9 %.

## **3. The dynamics of weed emergence in plots mulched with organic mulches and different thickness of mulch layer**

The carried out investigations show that mulching of soil with various organic mulches is particularly important in the first part of summer. In the second part of summer and at the beginning of autumn weed emergence is weaker in comparison with that in the period of spring and early summer, therefore, lower influence of mulch is established.

In 2004 common bean crop was damaged by spring frost for two times, particularly in plots mulched with sawdust. As crop was thin, intensive weed emergence in plots without mulching was lengthen out. According to the data of 2004, sawdust had the longest impeding effect on weed germination (Table 1). Though crop in plots mulched with sawdust was weak, weed emergence was not intensive: at the beginning of summer weed density was established to be by 5.4-11.4 times lower than that in the plots without mulching. The allelopatic effect of sawdust could be a reason of such results.

Peat, straw and grass provide different reducing impact on weed germination. Straw mulch has the most obvious reducing impact (3.5-14.1 times) on weed emergence in June. Later, however, after abundant appearance of *Tripleurospermum perforatum* (Merat.) M. Lainz, which seeds have infected the mulch, the weediness is higher than that in the soil without mulch (July 20). After most of seeds of *Tripleurospermum perforatum* have germinated, the positive influence of mulch comes out again.


\*- 95 % probability level, \*\* - 99 % probability level, \*\*\* - 99.9 % probability level

**Table 1.** The influence of different organic mulches on weed emergence dynamics in common bean crop, 2004

At the beginning of summer peat has slightly weaker impeding effect on weed emergence (4.2-7.0 times), which, however, is uniform during the entire investigational period. Positive effect of grass mulch is manifested at the beginning of the investigations and reduces weed germination from 17.8 to 2.7 times. Later, after decomposition of grass has started, this mulch has no significant influence. Experiments conducted in Hungary indicated that mulching with straw, grass and other materials showed good results in weed control [4].

**3. The dynamics of weed emergence in plots mulched with organic mulches**

The carried out investigations show that mulching of soil with various organic mulches is particularly important in the first part of summer. In the second part of summer and at the beginning of autumn weed emergence is weaker in comparison with that in the period of

In 2004 common bean crop was damaged by spring frost for two times, particularly in plots mulched with sawdust. As crop was thin, intensive weed emergence in plots without mulching was lengthen out. According to the data of 2004, sawdust had the longest impeding effect on weed germination (Table 1). Though crop in plots mulched with sawdust was weak, weed emergence was not intensive: at the beginning of summer weed density was established to be by 5.4-11.4 times lower than that in the plots without mulching. The allelopatic effect of

Peat, straw and grass provide different reducing impact on weed germination. Straw mulch has the most obvious reducing impact (3.5-14.1 times) on weed emergence in June. Later, however, after abundant appearance of *Tripleurospermum perforatum* (Merat.) M. Lainz, which seeds have infected the mulch, the weediness is higher than that in the soil without mulch (July 20). After most of seeds of *Tripleurospermum perforatum* have germinated, the positive influence

**Without mulching Straw Peat Sawdust Grass**

10 06 440.6 31.2\*\*\* 62.6\*\*\* 38.8\*\*\* 24.7\*\*\* 20 06 204.4 58.1\*\*\* 44.1\*\*\* 38.1\*\*\* 26.2\*\*\* 30 06 233.4 45.9\*\*\* 46.6\*\*\* 25.9\*\*\* 25.9\*\*\* 10 07 144.0 85.6\*\*\* 34.1 20.9\*\*\* 52.5\*\*\* 20 07 54.7 113.1 38.1 30.0\*\* 66.2 30 07 50.6 33.1 22.2\* 11.6\*\*\* 45.3 10 08 67.5 40.9\*\* 30.9\* 23.4\*\* 44.4\*\* 20 08 54.7 33.4\* 20.6\* 23.4\*\* 38.4 30 08 34.4 20.3\* 18.1\* 16.9\*\* 32.2 10 09 25.0 13.4 10.3 14.1 23.1 20 09 5.3 5.3 7.5 6.2 18.1 30 09 25.3 15.0 5.3\*\*\* 15.0\* 29.4 10 10 25.6 20.6 5.0\*\*\* 16.6 31.6 20 10 13.4 6.6\* 2.8\*\*\* 8.1\*\*\* 12.5

spring and early summer, therefore, lower influence of mulch is established.

**and different thickness of mulch layer**

68 Weed Biology and Control

sawdust could be a reason of such results.

**Sampling time Weeds units m-2**

\*- 95 % probability level, \*\* - 99 % probability level, \*\*\* - 99.9 % probability level

**Table 1.** The influence of different organic mulches on weed emergence dynamics in common bean crop, 2004

of mulch comes out again.

Even stronger positive influence of mulches on the decrease of weed emergence was deter‐ mined in 2005. Weed control means in common onion crop are very important because common onion crop hasn't good smothering effect on weeds. In contrast to that in previous years, straw mulch was the best to reduce weed germination, as the mulch itself was not infected with weed seeds (Table 2). A number of studies have documented that straw mulch is a good mean decreasing weed emergence [5, 6]. Though [39] stated that there was no significant effect of straw mulch on number of weeds, but they explain it was mainly attributed to the low amounts of straw applied.

The number of weeds that germinated in the beginning of summer in mulched soils was by 30.9-50.6 times lower than that in the soils without mulch. Later this positive influence weakened but remained for the entire vegetation period. Peat had the influence similar to that in the previous years of investigations.


\*- 95 % probability level, \*\* - 99 % probability level, \*\*\* - 99.9 % probability level

**Table 2.** The influence of different organic mulches on weed emergence dynamics in common onion crop, 2005

The effect of chopped grass remained until the first decade of August, the number of germi‐ nated weeds was significantly lower (by 2.0-32.9 times) than that in the plots without mulch. However, later the weed emergence became equal and even started increasing as rapid germination of *Poa annua* L., which might have got into together with the used mulch, started. During the entire vegetation period grass mulch decreased the germination of weeds by 2.0 times in comparison to that in the soil without mulch.

In 2006 mulches were spread late – after the red beet sprouting (Table 3). The first weed sampling time was before mulching. No significant differences in weed number between plots without mulching and plots mulched with different organic mulches were obtained. Though the highest number of weeds was estimated in plots where grass mulch in previous year was used, the grass mulch smothered weeds significantly till the end of September. Weed germi‐ nation and re-growth decreased on July 30, and the influence of straw, peat and sawdust mulches on weed number at this sampling time was not significant. In 2006 al examined organic mulches suppressed weeds in red beet crop very well.


● – before mulching

\*- 95 % probability level, \*\* - 99 % probability level, \*\*\* - 99.9 % probability level

**Table 3.** The influence of different organic mulches on weed emergence dynamics in red beet crop, 2006

All examined organic mulches significantly suppressed weed emergence during the most intensive weed germination period in May 30 (by 11.7-32.6 times) and June 10 (by 7.5-19.4 times) in 2007 (Table 4). The suppressing effect of organic mulches weakened when weakened weed germination (June 20). The significant suppressing grass mulch effect on weed emer‐ gence persisted till the August 10. In 2007 the grass mulch was the best means for weed control till the end of summer (August 30). During the first part of summer grass mulch effectively smothered weeds, and during the second part of summer white cabbage crop smothered weeds very well.


\*- 95 % probability level, \*\* - 99 % probability level, \*\*\* - 99.9 % probability level

The effect of chopped grass remained until the first decade of August, the number of germi‐ nated weeds was significantly lower (by 2.0-32.9 times) than that in the plots without mulch. However, later the weed emergence became equal and even started increasing as rapid germination of *Poa annua* L., which might have got into together with the used mulch, started. During the entire vegetation period grass mulch decreased the germination of weeds by 2.0

In 2006 mulches were spread late – after the red beet sprouting (Table 3). The first weed sampling time was before mulching. No significant differences in weed number between plots without mulching and plots mulched with different organic mulches were obtained. Though the highest number of weeds was estimated in plots where grass mulch in previous year was used, the grass mulch smothered weeds significantly till the end of September. Weed germi‐ nation and re-growth decreased on July 30, and the influence of straw, peat and sawdust mulches on weed number at this sampling time was not significant. In 2006 al examined

**Weeds units m-2**

**Without mulching Straw Peat Sawdust Grass**

10 06● 457.7 496.9 525.9 438.5 592.1 30 06 286.6 49.4\*\*\* 70.3\*\*\* 54.1\*\*\* 29.1\*\*\* 10 07 62.2 31.3\*\* 22.8\*\*\* 37.8 12.8\*\*\* 20 07 114.1 27.2\*\*\* 21.3\*\*\* 31.6\*\* 10.0\*\*\* 30 07 53.1 40.3 30.3 39.4 12.2\*\*\* 10 08 58.4 16.6\*\*\* 19.1\*\*\* 21.6\*\* 10.0\*\*\* 20 08 234.7 36.6\*\*\* 50.9\*\*\* 53.1\*\*\* 47.8\*\*\* 30 08 104.4 35.3\*\*\* 33.4\*\*\* 20.9\*\*\* 31.9\*\*\* 10 09 93.4 34.7\*\*\* 30.6\*\*\* 30.0\*\*\* 33.1\*\*\* 20 09 56.9 21.9\* 14.4\* 18.8\*\* 22.2\* 30 09 38.1 22.2\* 54.7 24.4 16.6\*\*\* 10 10 38.4 15.9\*\*\* 17.8\* 19.4\*\* 23.4

times in comparison to that in the soil without mulch.

organic mulches suppressed weeds in red beet crop very well.

\*- 95 % probability level, \*\* - 99 % probability level, \*\*\* - 99.9 % probability level

**Table 3.** The influence of different organic mulches on weed emergence dynamics in red beet crop, 2006

All examined organic mulches significantly suppressed weed emergence during the most intensive weed germination period in May 30 (by 11.7-32.6 times) and June 10 (by 7.5-19.4 times) in 2007 (Table 4). The suppressing effect of organic mulches weakened when weakened

**Sampling time**

70 Weed Biology and Control

● – before mulching

**Table 4.** The influence of different organic mulches on weed emergence dynamics in white cabbage crop, 2007

In 2008, potatoes after planting were harrowed, were hilled after sprouting and then mulches were spread. Spring in 2008 was very dry, without rainfall till the second half of June. Because of lack of humidity we had no grass mulch at the beginning of June. The grass mulch was polluted with matured weed seeds. The lowest number of weeds emerged at the first sampling date in June 20. Late weed germination and re-growth was intensive: weed number in plots without mulch at different sampling times varied from 109.7 to 651.6 units m-2 (Table 5). All examined organic mulches significantly suppressed weed emergence till the end of July. From that date the effect of grass mulch weakened, and the number of weeds in grass mulched plots exceeded the number of weeds in plots without mulch.

In 2009 straw and sawdust mulch significantly decreased weed emergence during all experimental period (Table 6). The significant suppressing effect of grass mulch ended at the end of July.


\*- 95 % probability level, \*\* - 99 % probability level, \*\*\* - 99.9 % probability level

**Table 5.** The influence of different organic mulches on weed emergence dynamics in potatoes crop, 2008


\*- 95 % probability level, \*\* - 99 % probability level, \*\*\* - 99.9 % probability level

**Table 6.** The influence of different organic mulches on weed emergence dynamics in common bean crop, 2009

**Perennial weeds.** The results of the experiments carried out in Lithuania showed that straw mulch suppressed emergence of annual weeds but not perennial [27]. By the data of our experiments, the effect of organic mulches on the germination and re-growth of perennial weeds is weaker than the effect of organic mulches on germination of annual weeds [7]. In 2007 at the end of spring (May 30) and at the beginning of summer (June 10) the higher amount of perennial weeds was established in experimental plots without mulching. Grass mulch well suppressed perennial weeds during all vegetation period (Fig. 2).

Contrary results were obtained in 2008: the germination and re-growth of perennial weeds was more intensive in unmulched plots during all sampling time. The lowest amount of perennial weeds was obtained in plots mulched with straw and grass mulches.

**Sampling time**

**Sampling time**

72 Weed Biology and Control

**Weeds units m-2**

**Weeds units m-2**

**Without mulching Straw Peat Sawdust Grass**

20 06 22.2 0.6\*\* 5.3\* 10.3 1.9\* 30 06 651.6 28.4\*\*\* 145.9\*\*\* 43.1\*\*\* 183.8\*\*\* 10 07 133.8 37.2\* 59.1 36.9\* 81.9\* 20 07 157.8 37.8\*\*\* 61.3\*\* 38.4\*\*\* 796.3\*\* 30 07 181.9 19.4\*\*\* 28.1\*\*\* 26.6\*\*\* 65.0\*\*\* 10 08 241.9 100.0 40.3\*\*\* 60.0\*\* 156.3 20 08 214.7 25.9\*\*\* 21.9\*\*\* 34.4\*\*\* 320.6 30 08 118.4 49.1 98.4 71.3 1947.2\*\*\* 10 09 109.7 60.6\* 27.8\*\*\* 19.4\*\*\* 438.8\*\*

**Without mulching Straw Peat Sawdust Grass**

10 06 313.4 27.8\*\*\* 199.4 20.9\*\*\* 46.9\*\*\* 20 06 293.4 14.1\*\*\* 106.9\*\*\* 36.3\*\*\* 20.9\*\*\* 30 06 205.4 14.4\*\*\* 50.9\*\*\* 20.6\*\*\* 47.7\*\*\* 10 07 150.0 17.1\*\*\* 22.3\*\*\* 17.2\*\*\* 25.7\*\*\* 20 07 82.2 5.2\*\*\* 14.5\*\*\* 11.1\*\*\* 10.4\*\*\* 30 07 66.1 5.6\*\*\* 9.1\*\*\* 13.3\*\*\* 15.6\*\* 10 08 45.6 8.4\* 12.5 23.4 48.1 20 08 47.8 14.4\*\* 9.1\*\*\* 14.7\*\* 50.6 30 08 37.9 8.8\*\* 4.4\*\*\* 10.3\* 72.2 10 09 22.5 11.6\*\* 9.2\*\*\* 12.8\* 104.5

**Table 5.** The influence of different organic mulches on weed emergence dynamics in potatoes crop, 2008

**Table 6.** The influence of different organic mulches on weed emergence dynamics in common bean crop, 2009

**Perennial weeds.** The results of the experiments carried out in Lithuania showed that straw mulch suppressed emergence of annual weeds but not perennial [27]. By the data of our experiments, the effect of organic mulches on the germination and re-growth of perennial weeds is weaker than the effect of organic mulches on germination of annual weeds [7]. In 2007 at the end of spring (May 30) and at the beginning of summer (June 10) the higher amount

\*- 95 % probability level, \*\* - 99 % probability level, \*\*\* - 99.9 % probability level

\*- 95 % probability level, \*\* - 99 % probability level, \*\*\* - 99.9 % probability level

– without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass. In 2009 the highest number of perennial weeds germinated and re-grew in plots without **Figure 2.** The influence of organic mulches on perennial weed emergence dynamics, 2007–2009. WM – without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass.

Figure 2. The influence of organic mulches on perennial weed emergence dynamics, 2007–2009. WM

mulching during all vegetation period. Significant differences between the number of perennial weeds in unmulched plots and plots mulched with different organic mulches were established at many sampling dates. **Annual weeds.** The period of more intensive germination of annual weeds is from the middle of May to the middle of June [40]. In 2007 all examined organic mulches well suppressed annual weed germination. The mulching as annual weed control means was particularly important at In 2009 the highest number of perennial weeds germinated and re-grew in plots without mulching during all vegetation period. Significant differences between the number of peren‐ nial weeds in unmulched plots and plots mulched with different organic mulches were established at many sampling dates.

The contrary results were obtained in 2008 when *Poa annua* germination in plots mulched with grass mulch germinated during all vegetation period. The number of germinated annual weeds in

the first part of summer (Fig.3).

sampling dates from the 20 of July.

**Annual weeds.** The period of more intensive germination of annual weeds is from the middle of May to the middle of June [40]. In 2007 all examined organic mulches well suppressed annual weed germination. The mulching as annual weed control means was particularly important at the first part of summer (Fig.3).

The contrary results were obtained in 2008 when *Poa annua* L. germination in plots mulched with grass mulch prolonged during all vegetation period. Grass mulch has been infected with seeds of *Poa annua*. The number of germinated annual weeds in grass mulched plots exceeded the number of annual weeds in unmulched plots during almost sampling dates from the 20 of July. The contrary results were obtained in 2008 when *Poa annua* germination in plots mulched with grass mulch germinated during all vegetation period. The number of germinated annual weeds in grass mulched plots exceeded the number of annual weeds in unmulched plots during almost

without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass. In 2009 the germination of annual weeds in unmulched plots was significantly more intensive till July 30 compared with germination of annual weeds in plots mulched with all examined organic **Figure 3.** The influence of organic mulches on annual weed emergence dynamics, 2007–2009. WM – without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass.

mulches (Fig. 3). From the beginning of August the suppressive effect of grass mulch on annual weed

Figure 3. The influence of organic mulches on annual weed emergence dynamics, 2007–2009. WM –

In 2009 the germination of annual weeds in unmulched plots was significantly more intensive till July 30 compared with germination of annual weeds in plots mulched with all examined organic mulches (Fig. 3). From the beginning of August the suppressive effect of grass mulch on annual weed germination disappeared. During this period the suppressive effect on annual weeds of straw, peat and sawdust mulches persisted.

### **4. The total weed amount influenced by mulching**

**Annual weeds.** The period of more intensive germination of annual weeds is from the middle of May to the middle of June [40]. In 2007 all examined organic mulches well suppressed annual weed germination. The mulching as annual weed control means was particularly important

The contrary results were obtained in 2008 when *Poa annua* L. germination in plots mulched with grass mulch prolonged during all vegetation period. Grass mulch has been infected with seeds of *Poa annua*. The number of germinated annual weeds in grass mulched plots exceeded the number of annual weeds in unmulched plots during almost sampling dates from the 20 of

**2007**

**2008**

The contrary results were obtained in 2008 when *Poa annua* germination in plots mulched with grass mulch germinated during all vegetation period. The number of germinated annual weeds in grass mulched plots exceeded the number of annual weeds in unmulched plots during almost

> **30 05 10 06 20 06 30 06 10 07 20 07 30 07 10 08 20 08 30 08 10 09 20 09 30 09 Sampling time**

**20 06 30 06 10 07 20 07 30 07 10 08 20 08 30 08 10 09**

**Sampling time**

**10 06 20 06 30 06 10 07 20 07 30 07 10 08 20 08 30 08 10 09 Sampling time**

Figure 3. The influence of organic mulches on annual weed emergence dynamics, 2007–2009. WM –

**Figure 3.** The influence of organic mulches on annual weed emergence dynamics, 2007–2009. WM – without mulch, ST

In 2009 the germination of annual weeds in unmulched plots was significantly more intensive till July 30 compared with germination of annual weeds in plots mulched with all examined organic mulches (Fig. 3). From the beginning of August the suppressive effect of grass mulch on annual weed

without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass.

**WM ST PT SD GR**

**2009**

at the first part of summer (Fig.3).

sampling dates from the 20 of July.

– straw, PT – peat, SD – sawdust, GR – grass.

**units m-2** 

**units m-2**

74 Weed Biology and Control

 **units m-2** 

July.

Mulching decreased weed density (Fig. 4). By the data of our experiments, the best for weed control is straw mulch. In plots with straw mulch weed density was established for 2.6-10.0 times lower compared with weed density in plots without mulch. Significant differences between weed density in plots mulched with peat and sawdust compared to weed density in plots without mulch were estimated.

The influence of grass mulch on weed emergence is not equal. In 2004-2009 (except 2008) grass mulch significantly decreased weed number – by 2.6-5.4 times compared with weed number in unmulched plots. In 2008 weed density in plots mulched with grass was established higher that is in plots mulched with straw, peat and sawdust due to rapid emergence of *Poa annua* at the second part of summer. In 2008 number *of Poa annua* formed a big part – 79.5% of total weed number, as in 2005 – 11.3%, 2006 – 4.9%, and 2007 – 5.1%.

**Figure 4.** The influence of organic mulches on weed density, 2004-2009. WM – without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass. \*- 95 % probability level, \*\* - 99 % probability level, \*\*\* - 99.9 % probability level

The influence of peat and sawdust mulch on weed density was significant during all experi‐ ment period in 2004–2009. Weed density in peat mulched plots was lower by 3.0-5.4 times compared with this in plots without mulch and weed density in sawdust mulched plots was lower (by 2.6-6.9 times) compared with this in plots without mulch. The growth of agricultural crops in plots with sawdust mulch was poor and the yield obtained was the lowest (Fig.5.).

Weed density in plots mulched with 10 cm mulch layer was lower compared with plots mulched with 5 cm mulch layer (Fig. 6). Differences were significant in 2004, 2006, 2008 and 2009. The thickness of mulch layer is important for weed control. Thick enough layer of organic mulch can serve as physical barrier for weeds.

Figure 5. Red beet crop in plots mulched with sawdust (a) and mulched with grass (b) **Figure 5.** Red beet crop in plots mulched with sawdust (a) and mulched with grass (b)

**480\*\*\***

Figure 6. The influence of different thickness of mulch layer on weed density, 2004-2009 yers. WM – without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass. \* – 95% probability level, \*\*\* – **Figure 6.** The influence of different thickness of mulch layer on weed density, 2004-2009 yers. WM – without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass. \* – 95% probability level, \*\*\* – 99,9% probability level

**4. Mulching effect on weed seed bank** 

seed bank in the soil in unmulched plots and plots mulched with different layer of organic mulches

#### The formation of weed seed bank is multiplex process, belonging on various factors. Weed **5. Mulching effect on weed seed bank**

99,9% probability level

was studied in 2007-2009, after three years from the beginning of the experiment. There was no significant influence of mulching on weed seed bank during all experimental period. The tendency of lower amount of weed seeds in the soil in plots mulched with straw, peat and sawdust was investigated. Only grass mulch increased the total amount of weed seeds in the soil. We used the grass regularly cut from grass-plots for mulching, but sometimes it could be polluted with weed seeds. Moreover, the grass mulch quickly decomposes and its effect on weed control is The formation of weed seed bank is multiplex process, belonging on various factors. Weed seed bank in the soil in unmulched plots and plots mulched with different layer of organic mulches was studied in 2007-2009, after three years from the beginning of the experiment. There was no significant influence of mulching on weed seed bank during all experimental period.

The tendency of lower amount of weed seeds in the soil in plots mulched with straw, peat and sawdust was investigated. Only grass mulch increased the total amount of weed seeds in the soil. We used the grass regularly cut from grass-plots for mulching, but sometimes it could be polluted with weed seeds. Moreover, the grass mulch quickly decomposes and its effect on weed control is shorter compared with other studied mulches. Some matured weeds seeds in grass mulched plots can supplement weed seed bank in the soil. It is very important to use the grass for mulching from plots which are cut every few days (4–7) if we are concerning about weed seed bank.

2009. The thickness of mulch layer is important for weed control. Thick enough layer of organic

Figure 5. Red beet crop in plots mulched with sawdust (a) and mulched with grass (b)

**612**

**363\***

**363\***

**2004 2005 2006 2007 2008 2009**

**5 cm 10 cm Mulch layer**

**2004 2005 2006 2007 2008 2009**

**427**

**562**

**5 cm 10 cm Mulch layer**

Figure 6. The influence of different thickness of mulch layer on weed density, 2004-2009 yers. WM – without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass. \* – 95% probability level, \*\*\* –

**4. Mulching effect on weed seed bank**  The formation of weed seed bank is multiplex process, belonging on various factors. Weed seed bank in the soil in unmulched plots and plots mulched with different layer of organic mulches was studied in 2007-2009, after three years from the beginning of the experiment. There was no

 The tendency of lower amount of weed seeds in the soil in plots mulched with straw, peat and sawdust was investigated. Only grass mulch increased the total amount of weed seeds in the soil. We used the grass regularly cut from grass-plots for mulching, but sometimes it could be polluted with weed seeds. Moreover, the grass mulch quickly decomposes and its effect on weed control is

significant influence of mulching on weed seed bank during all experimental period.

The formation of weed seed bank is multiplex process, belonging on various factors. Weed seed bank in the soil in unmulched plots and plots mulched with different layer of organic mulches was studied in 2007-2009, after three years from the beginning of the experiment. There was no significant influence of mulching on weed seed bank during all experimental

**Figure 6.** The influence of different thickness of mulch layer on weed density, 2004-2009 yers. WM – without mulch, ST

a) b)

**1610**

**1194\***

**1194\***

**660**

**660**

**480\*\*\***

**480\*\*\***

**562**

**427**

**1610**

mulch can serve as physical barrier for weeds.

76 Weed Biology and Control

**828**

**359\***

**828**

99,9% probability level

**5. Mulching effect on weed seed bank**

**units m-2**

**units m -2**

period.

**359\***

**551** **551**

**336**

**Figure 5.** Red beet crop in plots mulched with sawdust (a) and mulched with grass (b)

**336**

– straw, PT – peat, SD – sawdust, GR – grass. \* – 95% probability level, \*\*\* – 99,9% probability level

**612** Seeds of *Chenopodium album* L., *Echinochloa crus-galli* L. (Beuv.) and *Stelaria media* L. dominated in the weed seed bank of all experimental plots (Fig.7). It is known that seeds of *Chenopodium album* amount about 90% of weed seed bank [41].

**Figure 7.** The influence of organic mulches and different thickness of mulch layer on weed seedbank, 2007. WM – without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass. *P* > 0.05

The tendency of higher number of *Chenopodium album* seeds in the soil of grass mulched plots was observed in 2007 and 2008. The part of *Echinochloa crus-galli* seeds increased in 2008, especially in plots without mulch and plots mulched with peat (Fig.8).

**Figure 8.** The influence of organic mulches and different thickness of mulch layer on weed seedbank, 2008. WM – without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass. *P* > 0.05

In 2009 the lower total amount of weed seeds in the soil was evaluated in mulched and unmulched plots (Fig. 9). The number of seeds of *Echinochloa crus-galli* in unmulched plots and plots mulched with peat decreased, but in plots mulched with straw, sawdust and grass increased.

**Figure 9.** The influence of organic mulches and different thickness of mulch layer on weed seedbank, 2009. WM – without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass. *P* > 0.05

The tendency of the lower amount of weed seeds in the soil was established in plots mulched with thicker (10 cm) mulch layer compared with this in plots mulched with thinner (5 cm) mulch layer during all experiment period 2007–2009.

No significant correlation between the amount of sprouted weeds and weed seeds in the soil was established in 2007. Very strong or strong significant correlation between the amount of sprouted weeds and weed seeds in the soil was established in 2008 (*r* = 0.96; *P* < 0.05) and in 2009 (*r* = 0.92; *P* < 0.05). *Chenopodium album* L. was the dominant weed in crops and *Chenopodium album* seeds dominated in weed seed bank and influenced correlations.

#### **6. The residual effect of organic mulches on weed incidence in crop stands**

Soil coverage with any organic mulch inhibits weed emergence at first due to the shortage of light and changed moisture and warmth regime [25]. The previously six year used and incorporated organic mulches did not significantly decreased total weed amount in 2010–2012 because they do not mechanically suppress weed emergence (Fig. 10). Total weed number in experimental plots during 2010–2012 was influenced by weed smothering ability of crops. The lowest total weed number was evaluated in 2012 when white cabbage was grown, and the highest – in 2010, when the common onion was grown.

The tendency of lower amount of weeds in plots previously mulched with sawdust was established in 2011–2012. Due to allelophatic effect the decrease of growth and yield of agricultural crops in plots mulched with sawdust was evaluated in 2004-2012. Decreased weed density in plots mulched with sawdust was significantly lower in 2004-2009. Weeds could be

**Figure 10.** The residual effect of organic mulches on the weed emergence, 2010–2012; *P* > 0.050

In 2009 the lower total amount of weed seeds in the soil was evaluated in mulched and unmulched plots (Fig. 9). The number of seeds of *Echinochloa crus-galli* in unmulched plots and plots mulched with peat decreased, but in plots mulched with straw, sawdust and grass

**31.9 28.0**

**WM ST PT SD GR 5 cm 10 cm**

**37.6 32.6 30.1**

*Chenopodium album Galinsoga parviflora Echinochloa crus-galli Other weeds*

**Figure 9.** The influence of organic mulches and different thickness of mulch layer on weed seedbank, 2009. WM –

The tendency of the lower amount of weed seeds in the soil was established in plots mulched with thicker (10 cm) mulch layer compared with this in plots mulched with thinner (5 cm)

No significant correlation between the amount of sprouted weeds and weed seeds in the soil was established in 2007. Very strong or strong significant correlation between the amount of sprouted weeds and weed seeds in the soil was established in 2008 (*r* = 0.96; *P* < 0.05) and in 2009 (*r* = 0.92; *P* < 0.05). *Chenopodium album* L. was the dominant weed in crops and *Chenopodium*

**6. The residual effect of organic mulches on weed incidence in crop stands**

Soil coverage with any organic mulch inhibits weed emergence at first due to the shortage of light and changed moisture and warmth regime [25]. The previously six year used and incorporated organic mulches did not significantly decreased total weed amount in 2010–2012 because they do not mechanically suppress weed emergence (Fig. 10). Total weed number in experimental plots during 2010–2012 was influenced by weed smothering ability of crops. The lowest total weed number was evaluated in 2012 when white cabbage was grown, and the

The tendency of lower amount of weeds in plots previously mulched with sawdust was established in 2011–2012. Due to allelophatic effect the decrease of growth and yield of agricultural crops in plots mulched with sawdust was evaluated in 2004-2012. Decreased weed density in plots mulched with sawdust was significantly lower in 2004-2009. Weeds could be

increased.

78 Weed Biology and Control

**35.0**

**24.1**

without mulch, ST – straw, PT – peat, SD – sawdust, GR – grass. *P* > 0.05

mulch layer during all experiment period 2007–2009.

highest – in 2010, when the common onion was grown.

*album* seeds dominated in weed seed bank and influenced correlations.

**thousand units m**

 **-2**

> affected by the allelophaty too. But the strongest effect on weed emergence and re-growth was the effect of organic mulches as physical barrier.

> In 2010 and 2012 the higher weed emergence was established in plots previously mulched with thicker (10 cm) mulch layer (Fig. 11). But in 2011 significantly lower amount of emerged weeds was evaluated in mentioned plots.

**Figure 11.** The residual effect of the thickness of mulch layer on the weed emergence, 2010–2012; *P* > 0.050

The residual effect of organic mulches on the emergence of annual weeds was not significant (except plots with peat mulch in 2011), but not the same that on perennial weeds. In 2010, the first year after the use of organic mulches all of the previously used and incorporated organic mulches reduced the abundance of annual weeds during the entire vegetation period (Fig. 12). The residual effect of straw, peat and grass was weaker and tended to reduce (by 6.2–11.4 %) the abundance of annual weeds during vegetation. In 2011, when studying grass and peat residual effect a trend towards increasing (by 4.8–11.2 %) of abundance of annual weeds during the whole vegetation was established.

In 2012, the previously used and incorporated grass mulch significantly (by 1.3 times) increased emergence of annual weeds. The previously incorporated sawdust mulch reduced the abundance of annual weeds most markedly in all experimental years.

**Figure 12.** Residual effect of organic mulches on the emergence of annual weeds in 2010-2012; \* - 95.0% probability level

Species composition of annual weeds was determined during the 2010–2012. Out of annual weeds the most abundant emergence was exhibited by *Echinochloa crus–galli* (L.), *Galinsoga parviflora* and *Poa annua* L. The residual effect of organic mulches on the emergence of annual weeds was irregular. The previously incorporated thicker mulch layer tended to diminish *Galinsoga parviflora* and *Poa annua* L. emergence, and exhibited uneven effect on *Echinochloa crus–galli* (L.) emergence, compared with the thinner mulch layer.

**Perennial weeds.** In 2010, the previously used and incorporated straw, peat and sawdust mulches tended to increase (by 11.3–31.5 %) the abundance of perennial weeds during vegetation period; however, the increase was insignificant (Fig. 13). When investigating residual effect of grass mulch, we established a trend towards reduction (by 12.4 %) of regrowth of perennial weeds. In 2011, the previously used and incorporated straw and grass mulches tended to increase (by 7.9–30.1 %) re-growth of perennial weeds, while peat and sawdust mulches tended to reduce it (by 8.3–12.4 %); however, insignificantly. In 2012, no significant differences in the abundance of perennial weeds were established.

**Figure 13.** Residual effect of organic mulches on the emergence of perennial weeds in 2010-2012; there are no signifi‐ cant differences: *P* > 0.050

In 2010 and 2012, the previously incorporated thicker (10 cm) mulch layer tended to increase (by 5.8 %) the abundance of annual weeds, and in 2011 it significantly (by 13.8 %) reduced annual weed abundance, compared with the incorporated thinner mulch layer (Fig. 14).

Species composition of annual weeds was determined during the 2010–2012. Out of annual weeds the most abundant emergence was exhibited by *Echinochloa crus–galli* (L.), *Galinsoga parviflora* and *Poa annua* L. The residual effect of organic mulches on the emergence of annual weeds was irregular. The previously incorporated thicker mulch layer tended to diminish *Galinsoga parviflora* and *Poa annua* L. emergence, and exhibited uneven effect on *Echinochloa*

**Figure 12.** Residual effect of organic mulches on the emergence of annual weeds in 2010-2012; \* - 95.0% probability

**1215**

**1213**

**1352**

**2010 2011 2012**

**WM ST PT SD GR**

**905\***

**1273**

**Perennial weeds.** In 2010, the previously used and incorporated straw, peat and sawdust mulches tended to increase (by 11.3–31.5 %) the abundance of perennial weeds during vegetation period; however, the increase was insignificant (Fig. 13). When investigating residual effect of grass mulch, we established a trend towards reduction (by 12.4 %) of regrowth of perennial weeds. In 2011, the previously used and incorporated straw and grass mulches tended to increase (by 7.9–30.1 %) re-growth of perennial weeds, while peat and sawdust mulches tended to reduce it (by 8.3–12.4 %); however, insignificantly. In 2012, no

*crus–galli* (L.) emergence, compared with the thinner mulch layer.

**417**

**0**

cant differences: *P* > 0.050

**200**

**units m-2**

**400**

**600**

**545**

**1674**

**units m -2**

80 Weed Biology and Control

level

**1527**

**1483**

**1388**

**1569**

**464** **548**

significant differences in the abundance of perennial weeds were established.

**372** **484**

**365402**

**341**

**2010 2011 2012**

**Without mulching Straw Peat Sawdust Grass**

**Figure 13.** Residual effect of organic mulches on the emergence of perennial weeds in 2010-2012; there are no signifi‐

**326**

> **183**

**659**

**721**

**702**

**641**

**844\***

**154** **166** **169** **183**

Figure 14. Residual effect of the thickness of organic mulch layer on the emergence of annual and perennial weeds in 2010–2012; there are no significant differences: *P* > 0.050 **Figure 14.** Residual effect of the thickness of organic mulch layer on the emergence of annual and perennial weeds in 2010–2012; there are no significant differences: *P* > 0.050

In 2010, the previously used and incorporated thicker 10 cm mulch layer tended to increase (by 8.0 %) re-growth of perennial weeds, and in 2011–2012 to decrease it (by 12.5–17.1 %), compared with the thinner 5 cm mulch layer; however, insignificantly. Species composition of perennial weeds was determined. Of the perennial weeds the most In 2010, the previously used and incorporated thicker 10 cm mulch layer tended to increase (by 8.0 %) re-growth of perennial weeds, and in 2011–2012 to decrease it (by 12.5–17.1 %), compared with the thinner 5 cm mulch layer; however, insignificantly.

prevalent were: *Sonchus arvensis* L., *Rorippa palustris* (L.) Besser., *Mentha arvensis* L., *Cirsium arvense* (L.) Scop*.*, *Elytrigia repens* (L.) Nevski. and *Taraxacum officinale* F. H. Wigg*.*). The residual effect of organic mulches on the re-growth of perennial weeds was unequal. The six year used and incorporated thicker mulch layer tended to reduce the re-growth of *Mentha arvensis* L., *Rorippa palustris* (L.) Besser., *Elytrigia repens* (L.) Nevski. and *Taraxacum officinale* (F. H. Wigg*.*) and tended to increase the re-growth of *Cirsium arvense* (L.) Scop. The better re-growth of *Cirsium arvense* in plots mulched with straw, peat and sawdust was investigated in 2004–2007 [35]. The reasons for better *C. arvense* emergence in mentioned plots can be various. As remains of mulch after harvesting were inserted into the soil by ploughing, soil shear strength decreased. Regression analysis of experiment data confirmed relationship between number of *C. arvense* sprouts and soil shear strength. **Conclusions**  Species composition of perennial weeds was determined. Of the perennial weeds the most prevalent were: *Sonchus arvensis* L., *Rorippa palustris* (L.) Besser., *Mentha arvensis* L., *Cirsium arvense* (L.) Scop*.*, *Elytrigia repens* (L.) Nevski and *Taraxacum officinale* F. H. Wigg*.*). The residual effect of organic mulches on the re-growth of perennial weeds was unequal. The six year used and incorporated thicker mulch layer tended to reduce the re-growth of *Mentha arvensis*, *Rorippa palustris*, *Elytrigia repens* and *Taraxacum officinale* and tended to increase the re-growth of *Cirsium arvense*. The better re-growth of *Cirsium arvense* in plots mulched with straw, peat and sawdust was investigated in 2004–2007 [35]. The reasons for better *Cirsium arvense* emergence in mentioned plots can be various. As remains of mulch after harvesting were inserted into the soil by ploughing, soil shear strength decreased. Regression analysis of experiment data confirmed relationship between number of *Cirsium arvense* sprouts and soil shear strength.

## **7. Conclusions**


### **Author details**

Rita Pupalienė\* , Aušra Sinkevičienė, Darija Jodaugienė and Kristina Bajorienė

\*Address all correspondence to: rita.pupaliene@asu.lt

Aleksandras Stulginskis University, Institute of Agroecosystems and Soil Science, Akademija, Kaunas distr., Lithuania

#### **References**

**7. Conclusions**

82 Weed Biology and Control

*galli*.

**Author details**

Kaunas distr., Lithuania

Rita Pupalienė\*

proper choice are essential.

\*Address all correspondence to: rita.pupaliene@asu.lt

**1.** All investigated organic mulches reduced weed emergence. Positive effect of mulches was particularly obvious in the period of intensive germination of weeds. Straw, peat and sawdust had the strongest influence on the decrease of weed germination and re-growth.

**2.** Germination of annual weeds was significantly reduced by all organic mulches applied. Re-growth of perennial weeds was significantly reduced by straw (up to 4.5 times), peat (up to 3.0 times), sawdust (up to 3.5 times) and grass (up to 3.9 times) mulches, however,

**3.** The residual effect of organic mulches on weed emergence was not significant. When the physical barrier – organic mulches – disappeared, the amount of weeds in the crop increased. The tendency of lower annual weed density in plots previously mulched with sawdust was established during 2010-2012. The re-growth of perennial weeds changed differently: *Rorippa palustris*, *Elytrigia repens* was significantly reduced by straw and peat mulches (by up to 1.9 times), while the re-growth of *Sonchus arvensis* was significantly increased by straw and sawdust mulches (by up to 2.9 times) and that of *Cirsium arvense*

**4.** The influence of organic mulches and thickness of mulch layer on weed seedbank was not significant. The tendency of reduction of weed seedbank density was established in plots mulched with straw, peat and sawdust compared with plots without mulch and in plots with 10 cm mulch layer compared with plots with 5 cm mulch layer. Declining weed density in mulched plots decreased amount of weed seeds in the soil. But the amount of weed seeds in the soil may even increase when organic mulches are used. It is very important to make sure that mulches are not polluted with weed seeds. Dominant weed species in weed seedbank were: *Chenopodium album*, *Stellaria media* and *Echinochloa crus-*

**5.** Organic mulches have different effects on agrocenosis, they suppress weeds by different ways, therefore a good knowledge of the characteristics of mulching materials and their

, Aušra Sinkevičienė, Darija Jodaugienė and Kristina Bajorienė

Aleksandras Stulginskis University, Institute of Agroecosystems and Soil Science, Akademija,

Grass mulch quickly decomposed and its effect on weed density was shorter.

they had a diverse effect on species composition of perennial weeds.

by sawdust mulch (by up to 16.8 times).


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[15] Razifimbelo T., Barthes B., Larre–Larrouy M. C., De Luca E. F., Larent J. Y., Cerri C. C., Feller C., 2006.Effect of sugarcane residue management (mulching versus burn‐ ing) on organic matter in clayey Oxisol from southern Brazil. Agricultural Ecosys‐

[16] Brevault T., et al. Impact of a no–till with mulch soil management strategy on soil macrofauna communities in a cotton cropping system. Soil and Tillage Research

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84 Weed Biology and Control


[41] Grigas A. Land-tenure and soil pollution with weed seeds. Zemdirbyste=Agriculture. 1995;49. 90–111 (In Lithuanian).

## **Weed Control by Soil Tillage and Living Mulch**

Kęstutis Romaneckas, Egidijus Šarauskis, Dovilė Avižienytė and Aida Adamavičienė

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/60030

#### **1. Introduction**

[41] Grigas A. Land-tenure and soil pollution with weed seeds. Zemdirbyste=Agriculture.

1995;49. 90–111 (In Lithuanian).

86 Weed Biology and Control

Reduced soil tillage can be classified as minimum, sustainable, conservation, ploughless or zero tillage. For example, in the United Kingdom, such tillage systems are commonly referred to as non-inversion tillage. These different types of non-reversible soil tillage methods maintain at least 30% residue coverage on the soil surface [1]. In reduced soil tillage practices, residue coverage leads to lower moisture evapotranspiration, higher soil water content and soil structural stability, and more effective prevention of soil erosion [2-4]. Compared to conven‐ tional annual deep soil ploughing, reduced tillage may decrease technological production costs and improve the economic effectiveness of agricultural practices [5]. However, weed control in such soil tillage systems is more complex. Reduced soil tillage leads to different weed seed bank distributions in the soil and occasionally lower herbicide effectiveness, which delays the time of weed seed germination because of crop residue coverage [6] and other indices.

How much do different soil tillage systems influence the weed infestation of crops? First, weed stand density depends on the competition ability of the crop. Cereals generally have higher competitiveness than do cultivated crops (beet, maize, and potato). For example, Vakali et al. [7] showed that in deeply cultivated plots, the barley crop weed shoot biomass was 65–88% higher than that in reversibly tilled plots, but in rye no clear influence was found. Ozpinar and Ozpinar [8] established that shallow soil rototilling (compared with mouldboard ploughing) increased the total weed density by 72 and 58% in maize and vetch crops, while the differences in wheat were low. Similar results were found by Mashingaidze et al. [9]. In crop rotations with maize, the highest weed stand differences were obtained between mouldboard ploughing and no tillage technologies. Occasionally, no tillage resulted in up to 20 times more weed infestation [10]. The spread of perennial weeds was typically more evident [11]. However,

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Streit et al. [12] showed that for no tillage technologies without herbicides, the weed density was lower than that in conventional or minimum tillage.

Different soil tillage intensities may slightly change the diversity of weed species in crops. In a 23-year experiment by Plaza et al. [13], in minimally tilled plots there were more weed species than in not tilled or traditionally ploughed plots. In a 14-year experiment by Carter and Ivany [14], the weed species diversity was slightly lower in ploughed soil than in shallowly or not tilled soil. In addition, high weed infestation resulted in substantial reductions in maize yield [15].

Worldwide experiments of reduced soil tillage have been widely and well documented, but investigations with maize crops (especially using the no-tillage system) are quite new in lands with low level of herbicide practice.

In chemicalless (ecological, organic, biological or similar) farming systems common problem is high risk of weed infestation. Weeds rival with crops for space, light, water and nutrients. Lazauskas [16] formulated the law of crop productivity, "...crop performance, expressed by the total mass of crops and weeds, is relatively constant and may be defined by the equation: Y = A − bx; Y – crop yield, A – maximum crop productivity, x – weed mass and b – yield depression coefficient". According to this law, the crop yield is inversely proportional to the crop weed mass. Rusu et al. [17] found similar results and concluded that maize green mass production losses could be considered equal to the mass of green weeds.

Living mulches (additional component of agrocenosis) can be useful for effective weed control [18]. According to the Lazauskas law, interseeded living mulch occupies part of total bioproduction and may decrease weed infestation. Nakamoto and Tsukamoto [19] found that "living mulches are cover crops that are maintained as a living ground cover throughout the growing season of the main crop". The winter rye (*Secale cereale* L.), ryegrasses (*Lolium* spp.) and subterranean clover (*Trifolium subterraneum* L.) might be used to suppres weeds in corn crop (*Zea mays* L.) [20]. However, living mulches can compete for nutrients and water with the main crop and yields of crop could decrease [21, 22]. As a result, living mulch plants often must be mechanically or chemically controlled [23, 24].

#### **2. Impact of different primary soil tillage methods on weed infestation**

Soil tillage is the main method to control weeds. The most valuable is primary soil tillage. For answer how effective primary soil tillage methods are, the long-term stationary field experi‐ ment is being conducted at Aleksandras Stulginskis University's (up to 2011 Lithuanian University of Agriculture) Experimental Station. The field experiment was set up in 1988 in the then Lithuanian Academy of Agriculture's Experimental Station. The soil of the experi‐ mental field is *Endohypogleyic-Eutric Planosol – PLe-gln-w*. The thickness of the soil ploughlayer is 23–27 cm. Soil texture – loam on heavy loam. The upper part of the ploughlayer (0–15 cm) contained: pHKCL – 6.6–7.0, available phosphorus – 131.1–206.7 mg kg-1, available potassium – 72.0–126.9 mg kg –1. Primary tillage methods investigated: 1. Conventional ploughing at 23– 25 cm depth (CP) (control treatment); 2. Shallow ploughing at 12–15 cm depth (SP); 3. Deep cultivation at 23–25 cm depth (DC); 4. Shallow cultivation at 12–15 cm depth (SC); 5. Not tilled soil (direct sowing) (NT). Crop rotation in the experiment: 1) spring rape; 2) winter wheat; 3) maize; 4) spring barley. The experiment involved 4 replications. Each crop was cultivated in 20 plots. The initial size of plots was 126 m2 (14 x 9 m), and the size of record plots was 70 m2 (10 x 7 m). The plots of the experimental treatments were laid out in a randomised order. The protection band of the plot was of 1 m width and that between replications of 9 m width. After crop harvesting, all experimental plots (except for treatment 5) were cultivated by a disc stubble cultivator Väderstad CARRIER 300 at the 12–15 cm depth. JOHN DEERE 6620 tractor was used in the experiment. According to the experimental design, primary tillage was performed in August–September (for winter wheat) or in October (for spring crops). The soil was ploughed with a conventional plough Gamega PP-3-43 with semi-helical mouldboards at the 23–25 cm depth (treatment 1) or at the 12–15 cm depth (treatment 2). Deep cultivation was carried out by a ploughlayer's cultivator (chisel) KRG-3.6 at the 23–25 cm depth (treatment 3). The plots of treatment 4 were additionally cultivated by a disc stubble cultivator Väderstad CARRIER 300 at the 12–15 cm depth. The plots of treatment 5 were not tilled.

Streit et al. [12] showed that for no tillage technologies without herbicides, the weed density

Different soil tillage intensities may slightly change the diversity of weed species in crops. In a 23-year experiment by Plaza et al. [13], in minimally tilled plots there were more weed species than in not tilled or traditionally ploughed plots. In a 14-year experiment by Carter and Ivany [14], the weed species diversity was slightly lower in ploughed soil than in shallowly or not tilled soil. In addition, high weed infestation resulted in substantial

Worldwide experiments of reduced soil tillage have been widely and well documented, but investigations with maize crops (especially using the no-tillage system) are quite new in lands

In chemicalless (ecological, organic, biological or similar) farming systems common problem is high risk of weed infestation. Weeds rival with crops for space, light, water and nutrients. Lazauskas [16] formulated the law of crop productivity, "...crop performance, expressed by the total mass of crops and weeds, is relatively constant and may be defined by the equation: Y = A − bx; Y – crop yield, A – maximum crop productivity, x – weed mass and b – yield depression coefficient". According to this law, the crop yield is inversely proportional to the crop weed mass. Rusu et al. [17] found similar results and concluded that maize green mass

Living mulches (additional component of agrocenosis) can be useful for effective weed control [18]. According to the Lazauskas law, interseeded living mulch occupies part of total bioproduction and may decrease weed infestation. Nakamoto and Tsukamoto [19] found that "living mulches are cover crops that are maintained as a living ground cover throughout the growing season of the main crop". The winter rye (*Secale cereale* L.), ryegrasses (*Lolium* spp.) and subterranean clover (*Trifolium subterraneum* L.) might be used to suppres weeds in corn crop (*Zea mays* L.) [20]. However, living mulches can compete for nutrients and water with the main crop and yields of crop could decrease [21, 22]. As a result, living mulch plants often

**2. Impact of different primary soil tillage methods on weed infestation**

Soil tillage is the main method to control weeds. The most valuable is primary soil tillage. For answer how effective primary soil tillage methods are, the long-term stationary field experi‐ ment is being conducted at Aleksandras Stulginskis University's (up to 2011 Lithuanian University of Agriculture) Experimental Station. The field experiment was set up in 1988 in the then Lithuanian Academy of Agriculture's Experimental Station. The soil of the experi‐ mental field is *Endohypogleyic-Eutric Planosol – PLe-gln-w*. The thickness of the soil ploughlayer is 23–27 cm. Soil texture – loam on heavy loam. The upper part of the ploughlayer (0–15 cm) contained: pHKCL – 6.6–7.0, available phosphorus – 131.1–206.7 mg kg-1, available potassium – 72.0–126.9 mg kg –1. Primary tillage methods investigated: 1. Conventional ploughing at 23–

production losses could be considered equal to the mass of green weeds.

must be mechanically or chemically controlled [23, 24].

was lower than that in conventional or minimum tillage.

reductions in maize yield [15].

88 Weed Biology and Control

with low level of herbicide practice.

In spring, after the soil had reached maturity stage, it was shallow-cultivated by a cultivator Laumetris KLG-3.6 (except for the plots of treatment 5), fertilizers were applied by a fertilizer spreader AMAZONE-ZA-M-1201. Pre-sowing, the soil was cultivated at a seed placement depth. The crops were sown by the following sowing machines: Väderstad Super Rapid 400C in 2010, Väderstad Rapid 300C Super XL in 2011 and in 2012. Herbicides and insecticides were sprayed by a sprayer AMAZONE UF-901. Spring rape and winter wheat plots were harvested by a small plot combine harvester "Sampo-500'' in 2010 and 2011 and by "Wintersteiger Delta'' in 2012. Spring barley was harvested by a small plot combine harvester "Sampo-500'' in 2010 and by "Wintersteiger Delta'' in 2011 and 2012.

Spring rape. Cultivars 'Hunter' in 2010, 'SW Landmark' in 2011 and 'Fenja' in 2012 were sown at a rate of 2–2.3 million seeds ha-1 at the 2–3 cm depth. Fertilizers were incorporated at the 2.5 cm depth. Sowing was performed by a continuous-row method with 12.5 cm wide inter-rows.

Winter wheat. Cultivar 'Ada' in 2010–2012 was sown at a seed rate of 4.5–5 million seeds ha-1 at the 4–5 cm depth. Fertilizers were incorporated at the 6 cm depth. Sowing was performed by a continuous-row method with 12.5 cm wide inter-rows.

Maize. Hybrids 'Pioneer P 8000 (x6T584)' in 2010, 'Pioneer P 8000 (x027)' in 2011 and 'Es capris' in 2012 were sown at a seed rate of 100 thousand seeds ha-1 at the 6 cm depth. Fertilizers were incorporated at the 6.5 cm depth. Sowing was performed by a continuous band wide-row method with 50 cm wide inter-rows (between bands), 12.5 cm wide inter-rows between rows.

Spring barley. Cultivars 'Simba' in 2010 and 2012, 'Tokada' in 2011 were sown at a seed rate of 5–6 million seeds ha-1 at the 3.5 cm depth. Fertilizers were applied by placement method at the 4–4.5 cm depth. Sowing was performed by a continuous-row method with 12.5 cm wide inter-rows.

Weed seed bank in the soil was determined in treatments 0–5 (1 and 5 treatments) at the 0–15, 15–25 cm depths after primary tillage in 20 spots of a record plot in 2010 and 2012. The samples were taken with an auger, and a composite sample was formed. Sampling at the 0–5 cm depth was done to compare the weed seed bank in the upper ploughlayer of the conventionally tilled and not tilled plots. A 100 g dry soil sample was placed on a sieve with 0.25 mm mesh diameter and washed with running water until small soil particles washed out. Weed seeds and the remaining mineral soil fraction were separated from the organic soil fraction using saturated salt (or potash) solution [25].

Crop weed incidence was assessed by identifying weed species composition, weed number at the beginning of vegetation or at resumption of vegetation (winter wheat) during intensive weed growth. Dry weed weight was determined at the end of crops vegetation. Weed incidence was assessed in 10 spots of a record plot in 0.06 m2 area. At the beginning of vegetation, weed seedlings were counted (weed seedlings m-2), and at the end of vegetation weed number (weeds m-2) and dry matter weight (g m-2) were established. The weeds were pulled out, dried to air-dry weight, and analysis of their botanical species composition was conducted [26].

The research data were statistically processed by the analysis of variance and correlationregression analysis methods. Software ANOVA was used when estimating the least significant difference LSD05 and LSD01. The correlation-regression analysis of the research data was conducted using software STAT and SIGMA PLOT. In the case of significant difference between the specific treatment and the control (reference treatment), the probability level was marked as:


#### **2.1. Weed seed-bank in the soil**

The effectiveness of weed control mainly depends on the ability to sweep out weed seed-bank and to prevent the addition with newer ones [27].

Analysis of the data on the effects of different primary tillage on weed seed bank in the soil revealed that nearly in all cases both in not tilled plots and conventionally deep-ploughed plots weed seed bank in the upper ploughlayer (0–5 cm depth) did not differ significantly (data are not presented). In deeper layer (0–15 cm depth) weed seed bank in reduced tillage treatments generally increased, except for not tilled plots, where weed seed bank was less abundant. Only single significant differences were established (Tables 1-4). In the samples taken from the 15– 25 cm depth, the weed seed bank was generally smaller. The seeds of annual weeds prevailed in the soil. In many cases, having reduced tillage, the ploughlayer differentiated into upper layer characterized by more abundant weed seed bank (60.1 % of the total weed seed bank) and bottom layer characterized by less abundant weed seed bank (39.9 %). Weed seeds found in conventionally ploughed soil, at the 0–15 cm depth, in different crops accounted for 51.3 to 52.9 % of the total weed seed bank, and in the 15–25 cm depth – from 47.1 to 48.5 %, in shallowploughed soil – 55.9–68.6 and 31.4–44.1 %, respectively, in deep-cultivated soil – 50.0–75.9 and 24.1–50.0 %, in shallow-cultivated soil – 50.0–70.8 and 29.2–50.0 %, in not tilled soil – 56.0-64.3 and 35.7–44.0 %.


The most widespread were annual weed's seeds: Chenopodium album, *Polygonum lapathifo‐ lia*, *Echinochloa crus-galli* and *Sinapis arvensis* L.

were taken with an auger, and a composite sample was formed. Sampling at the 0–5 cm depth was done to compare the weed seed bank in the upper ploughlayer of the conventionally tilled and not tilled plots. A 100 g dry soil sample was placed on a sieve with 0.25 mm mesh diameter and washed with running water until small soil particles washed out. Weed seeds and the remaining mineral soil fraction were separated from the organic soil fraction using saturated

Crop weed incidence was assessed by identifying weed species composition, weed number at the beginning of vegetation or at resumption of vegetation (winter wheat) during intensive weed growth. Dry weed weight was determined at the end of crops vegetation. Weed incidence was assessed in 10 spots of a record plot in 0.06 m2 area. At the beginning of vegetation, weed seedlings were counted (weed seedlings m-2), and at the end of vegetation weed number (weeds m-2) and dry matter weight (g m-2) were established. The weeds were pulled out, dried to air-dry weight, and analysis of their botanical species composition was conducted [26].

The research data were statistically processed by the analysis of variance and correlationregression analysis methods. Software ANOVA was used when estimating the least significant difference LSD05 and LSD01. The correlation-regression analysis of the research data was conducted using software STAT and SIGMA PLOT. In the case of significant difference between the specific treatment and the control (reference treatment), the probability level was

The effectiveness of weed control mainly depends on the ability to sweep out weed seed-bank

Analysis of the data on the effects of different primary tillage on weed seed bank in the soil revealed that nearly in all cases both in not tilled plots and conventionally deep-ploughed plots weed seed bank in the upper ploughlayer (0–5 cm depth) did not differ significantly (data are not presented). In deeper layer (0–15 cm depth) weed seed bank in reduced tillage treatments generally increased, except for not tilled plots, where weed seed bank was less abundant. Only single significant differences were established (Tables 1-4). In the samples taken from the 15– 25 cm depth, the weed seed bank was generally smaller. The seeds of annual weeds prevailed in the soil. In many cases, having reduced tillage, the ploughlayer differentiated into upper layer characterized by more abundant weed seed bank (60.1 % of the total weed seed bank) and bottom layer characterized by less abundant weed seed bank (39.9 %). Weed seeds found in conventionally ploughed soil, at the 0–15 cm depth, in different crops accounted for 51.3 to 52.9 % of the total weed seed bank, and in the 15–25 cm depth – from 47.1 to 48.5 %, in shallowploughed soil – 55.9–68.6 and 31.4–44.1 %, respectively, in deep-cultivated soil – 50.0–75.9 and 24.1–50.0 %, in shallow-cultivated soil – 50.0–70.8 and 29.2–50.0 %, in not tilled soil – 56.0-64.3

salt (or potash) solution [25].

90 Weed Biology and Control

\* – differences significant at 95 % probability level;

\*\* – differences significant at 99 % probability level.

and to prevent the addition with newer ones [27].

**2.1. Weed seed-bank in the soil**

marked as:

and 35.7–44.0 %.

Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 1.** The impact of different primary tillage on the number of weed seeds per 100 g of soil in spring oilseed-rape cultivation


Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 2.** The impact of different primary tillage on the number of weed seeds per 100 g of soil in winter wheat cultivation


Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 3.** The impact of different primary tillage on the number of weed seeds per 100 g of soil in maize cultivation


Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 4.** The impact of different primary tillage on the number of weed seeds per 100 g of soil in spring barley cultivation

According to the K. S. Torresen et al. [28] investigations, in top layer of minimally tilled soil there was found higher number of weed seeds than in 10-20 cm depth. Our investigations partlyš comfirms that findings, arable layer devited into upper one with higher number of weed seeds (60.1 % of total number) and deeper layer with less quantity of seeds (Table 5).


**Table 5.** The impact of different primary tillage on quantity of weed seeds after primary soil tillage, %, data averaged over 2010 and 2012.

#### **2.2. Weed spread**

**Soil tillage method Years Sampling depth cm**

Conventional ploughing 2010 30 26

Shallow ploughing 2010 49 25

Deep cultivation 2010 71\* 15

Shallow cultivation 2010 52 17

No-tillage 2010 21 12

Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 %

**Table 3.** The impact of different primary tillage on the number of weed seeds per 100 g of soil in maize cultivation

**Soil tillage method Years Sampling depth cm**

Conventional ploughing 2010 23 13

Shallow ploughing 2010 26 15

Deep cultivation 2010 27 28\*

Shallow cultivation 2010 24 14

No-tillage 2010 20 8

Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 %

According to the K. S. Torresen et al. [28] investigations, in top layer of minimally tilled soil there was found higher number of weed seeds than in 10-20 cm depth. Our investigations partlyš comfirms that findings, arable layer devited into upper one with higher number of weed seeds (60.1 % of total number) and deeper layer with less quantity of seeds (Table 5).

**Table 4.** The impact of different primary tillage on the number of weed seeds per 100 g of soil in spring barley

probability level.

92 Weed Biology and Control

probability level.

cultivation

0–15 15–25

0–15 15–25

2012 13 15

2012 14 16

2012 17 12

2012 15 12

2012 13 12

2012 14 20

2012 12 15

2012 14 12

2012 19 9

2012 17 11

Analysis of the data on the effect of different primary tillage on the weed incidence in the crops at the beginning of vegetation revealed that almost in all the cases of reduced tillage or direct drilling into not tilled plots, the number of weeds increased; however, significant difference was estimated only for not tilled winter wheat plots (Tables 6-9). In conventional ploughing treatment, the spread of annual weeds was more intensive. Having replaced conventional ploughing by shallow ploughing, deep and shallow cultivation and direct drilling, the number of annual weeds tended to decrease, while that of perennial weeds tended to increase.



Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 6.** The impact of different primary tillage on weed spread (number m-2) at the beginning of spring oilseed rape vegetation


Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 7.** The impact of different primary tillage on weed spread (number m-2) at the beginning of winter wheat vegetation



**Soil tillage methods Years**

**Soil tillage methods Years**

NT

94 Weed Biology and Control

CP

SP

DC

SC

NT

CP

SP

probability level.

vegetation

probability level.

vegetation

**Groups of weeds annual perennial total**

**Groups of weeds annual perennial total**

**annual perennial total**

2012 523.3 42.5 565.8

2010 29.2 12.5 41.7 2011 147.9 124.6 272.5 2012 320.4 225.8\* 546.2

2010 113.3 3.8 117.1 2011 109.2 0.0 109.2

2010 108.8 5.4 114.2 2011 106.3 3.7 110.0

2010 317.5\*\* 6.7 324.2\*\* 2011 99.6 15.4\* 115.0

2010 201.2 6.7 207.9 2011 102.5 17.5\*\* 120.0

2010 123.8 1.7 125.5 2011 47.1\* 0.8 47.9\*

2010 445.9 18.4 464.3 2011 305.4 13.4 318.8 2012 188.4 47.9 236.3

2010 616.3 24.2 640.5\* 2011 395.4 11.3 406.7

Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 %

**Table 7.** The impact of different primary tillage on weed spread (number m-2) at the beginning of winter wheat

**Soil tillage methods Years Groups of weeds**

Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 %

**Table 6.** The impact of different primary tillage on weed spread (number m-2) at the beginning of spring oilseed rape

Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 8.** The impact of different primary tillage on weed spread (number m-2) at the beginning of maize vegetation


Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 9.** The impact of different primary tillage on weed spread (number m-2) at the beginning of spring barley vegetation

At the end of vegetation, the weed incidence in reduced-tillage or not tilled plots increased in all cases compared with the control; however, the difference was not significant. Reduced tillage and direct drilling generally tended to increase the number of both annual and perennial weeds (Tables 10-13).


Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 10.** The impact of different primary tillage on weed spread at the end of spring oilseed-rape vegetation



tillage and direct drilling generally tended to increase the number of both annual and perennial

number m-2 mass

**Groups of weeds annual perenial total**

g m-2 number m-2 mass

g m-2 number m-2 mass

g m-2

g m-2

g m-2 number m-2 mass

2010 80.4 77.2 9.6 6.6 90.0 83.8 2011 172.9 139.8 15.4 45.6 188.3 185.4 2012 483.4 335.7 11.6 5.5 495.0 241.2

2010 125.0 127.8 13.3 21.4 138.3 149.2 2011 140.8 110.3 19.6 32.2 160.4 142.5 2012 487.9 355.9 19.2 19.4 507.1 375.3

2010 256.2\*\* 123.3 18.8 21.6 275.0\*\* 144.9 2011 210.8 76.5 40.4\* 167.7\* 251.2 244.2 2012 552.1 227.8 22.5 42.7 574.6 270.5

2010 219.5\* 157.4\* 13.8 48.2\* 233.3\*\* 205.6\* 2011 190.8 93.8 38.3 91.0 229.1 184.8 2012 605.0 340.2 20.0 12.3 625.0 352.5

2010 304.6\*\* 54.6 15.8 8.0 320.4\*\* 62.6 2011 275.0 106.1 6.2 4.6 281.2 110.7 2012 408.8 215.7 40.0\* 16.9 448.8 232.6

> **Groups of weeds annual perenial total**

> > g m-2 number m-2 mass

2010 33.8 2.9 21.2 2.3 55.0 5.2 2011 57.9 3.6 15.8 10.8 73.7 14.4 2012 81.7 20.6 60.8 100.2 142.5 120.8

2010 32.5 3.2 20.8 2.2 53.3 5.4 2011 90.0 3.5 25.8 44.9\* 115.8 48.4\* 2012 43.7 9.6 73.8 292.2\* 117.5 301.8

Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 %

**Table 10.** The impact of different primary tillage on weed spread at the end of spring oilseed-rape vegetation

number m-2 mass

weeds (Tables 10-13).

96 Weed Biology and Control

**Years**

**Soil tillage methods**

CP

SP

DC

SC

NT

probability level.

**Soil tillage methods**

CP

SP

**Years**

Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 11.** The impact of different primary tillage on weed spread at the end of winter wheat vegetation


Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 12.** The impact of different primary tillage on weed spread at the end of maize vegetation


Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 13.** The impact of different primary tillage on weed spread at the end of spring barley vegetation

There were found 21-22 species of weeds in experiment. The most widespread were: *Cheno‐ podium album* L., *Echinochloa crus-galli* L., *Polygonum lapathifolia* L., *Sonchus arvensis* L., *Cirsium arvense* L. Scop. and *Elytrigia repens* L. Nevski.

The correlation-regression analysis of the experimental data revealed that the spread of weeds partly depended on the soil structure and its stability, penetration resistance of deeper soil layers (35–50 cm), moisture content in the upper ploughlayer, soil phosphorus and potassium status, pH, crop stand density, amount of plant residues in the soil surface and weed seed bank in the ploughlayer.

#### **3. Impact of living mulch on weed infestation**

Numerous research and observations have been conducted aiming to establish weed spread methods and reasons and weed-crop competition peculiarities. Enhancement of the competi‐ tive ability of agricultural crops is one of the principal tools to increase the productivity of agricultural crops. Sowing living mulches between the rows of a main crop is a weed control method that does not employ herbicide application. Living mulches result in reduced field weed infestation and an increase in crop yield. From the ecological viewpoint, this technology is promising and beneficial. The study was aimed to establish the competitive peculiarities of the multi-component agrocenosis (maize, living mulches, weeds) and its effects on soil properties under sustainable farming conditions. Experimental object – different species of living mulch plants and maize monocrop. Research was conducted during 2009–2011 at the Lithuanian University of Agriculture (since 2011 Aleksandras Stulginskis University), Experimental Station. The soil of the experimental field was *Calc(ar)i-Epihypogleyic Luvisol LVgp-w-cc* [29] with a texture of silty light loam on heavy loam. The soil pHKCl measured 7.1, available phosphorus 134.83 mg kg-1, available potassium 74.66 mg kg-1. The soil in this territory has formed on a bottom morain or bottom glacial formations, covered by glacial lacustrine sedimentary rock and is a continuation of the Lithuanian Middle Plain. The layer of the sedimentary rock is of different thickness.

A one-factor, stationary field experiment was conducted. Different living mulches inter-seeded in maize inter-rows were tested.


**Soil tillage methods**

98 Weed Biology and Control

CP

SP

DC

SC

NT

probability level.

in the ploughlayer.

**Years**

number m-2 mass

**Groups of weeds annual perenial total**

g m-2 number m-2 number m-2 mass

2010 231. 6 109.6 16.7 5.2 248.3 114.8 2011 167.1 11.4 8.3 4.9 175.4 16.3 2012 31.6 7.3 21.7 13.8 53.3 21.1

2010 386.7 135.0 17.1 6.3 403.8 141.3 2011 263.8 23.9 13.3 15.0 277.1 38.9 2012 37.5 2.9 22.5 7.2 60.0 10.1

2010 785.0\* 173.2 23.8 26.8 808.8\* 200.0 2011 289.6 34.6\* 5.4 2.0 295.0 36.6 2012 71.2 9.2 39.6 17.9 110.8 27.1

2010 384.6 110.5 16.7 13.4 401.3 123.9 2011 371.2 30.4 10.0 5.6 381.2 36.0 2012 184.6\*\* 20.1\* 40.0 30.2 224.6\*\* 50.3\*

2010 778.3\* 156.5 10.0 6.4 788.3\* 162.9 2011 193.3 27.8 31.7\* 80.0\* 225.0 107.8\*\* 2012 35.0 9.1 24.2 3.0 59.2 12.1

Note: \* – significant differences from control treatment (conventional ploughing) at 95 % probability level, \*\* – at 99 %

There were found 21-22 species of weeds in experiment. The most widespread were: *Cheno‐ podium album* L., *Echinochloa crus-galli* L., *Polygonum lapathifolia* L., *Sonchus arvensis* L., *Cirsium*

The correlation-regression analysis of the experimental data revealed that the spread of weeds partly depended on the soil structure and its stability, penetration resistance of deeper soil layers (35–50 cm), moisture content in the upper ploughlayer, soil phosphorus and potassium status, pH, crop stand density, amount of plant residues in the soil surface and weed seed bank

Numerous research and observations have been conducted aiming to establish weed spread methods and reasons and weed-crop competition peculiarities. Enhancement of the competi‐

**Table 13.** The impact of different primary tillage on weed spread at the end of spring barley vegetation

*arvense* L. Scop. and *Elytrigia repens* L. Nevski.

**3. Impact of living mulch on weed infestation**

g m-2 number m-2


In all experimental years, the same living mulches were inter-seeded in the inter-rows of maize monocrop. The plots of the control treatment were weeded out twice. The experiment was replicated four times. The plots were laid out in a randomised design. The total area of an experimental plot was 24 m2 , and the area of a record plot was 20 m2 . In 2009, black fallow preceded maize and in 2010–2011 maize was monocropped.

Maize monocrop inter-seeded with living mulches was grown without chemical pest control under arable agriculture conditions. In spring, when the soil had reached physical maturity, complex NPK 16:16:16 fertilizer at a rate of 300 kg ha-1 was applied, and later the soil was loosened at 4–5 cm depth. Maize was sown by a pneumatic-mechanical drill Köngskilde PRECI – SEM with 50 cm-wide inter-rows and 16–17 cm distance between seeds. Post-emergence of maize, inter-rows were loosened and living mulches were sown with a 7-row manuallyoperated greenhouse seeder. The marginal rows of the inter-seeded living mulches were at 1– 2 cm distance from maize. In each experimental year, living mulches were inter-seeded in the plots in the same places. Living mulches were cut and chopped 2–3 times at maize growth stages BBCH 15–16, 31–32 and 63–65. BBCH 15–16 is leaf development stage when average maize height is 10–12 cm (Photo 1). BBCH 31–32 is stem elongation stage when 1–2 nodes are visible and maize height is 56–63 cm. BBCH 63–65 is maize flowering stage when the plant height is 70–215 cm. At flowering stage, the living mulch was cut only in 2009.

Later the practice was abandoned since tractor-hitched implement would not be able to do this. Mulches were cut with a hand-operated brush cutter "Stihl" FS – 550, using a designed and manufactured trolley, reducing the operator's load, with a protection hood, which evenly spreads the mulch in the inter-row and protects the crop from mechanical damage. Living mulches were cut after they had reached a height of up to 20–25 cm. Green mass of the living mulches was spread in maize inter-rows. At stem elongation stage (BBCH 31–32), the maize crop was additionally fertilized with nitrogen (N60). When fertilizing at 250 kg N ha-1 rate, no significant differences were observed between maize cultivation systems. The objective of our experiment was to determine the competition among living mulches, maize and weeds; therefore the total nitrogen rate selected was as low as 108 kg N ha-1. Maize samples for the determination of productivity were hand-cut at the end of September – middle of October (BBCH 87–88) at maize physiological maturity stage. After harvesting, the remaining plant residues were ploughed in by a reversible plough with semi-helical mouldboards at the 20–22 cm depth.

A hybrid maize cultivar 'Silvestre' was used in our experiment. Gul et al. [30] have reported that a denser maize crop increased competition between maize and weeds. As a result, the seed rate of maize in our experiment was 130–138 thousand seeds ha-1 or (20–23 kg ha-1). Spring rape (cv. 'Sponsor'), white mustard (cv. 'Braco'), Italian ryegrass (cv. 'Avance'), black medic (cv. 'Arka'), Persian clover (cv. 'Gorby'), red clover (cv. 'Nemuniai') (Photo 2) were sown at a seed rate of 10 kg ha-1, and spring barley (cv. 'Simba') was sown at a rate of 200 kg ha-1.

The first assessment of weed infestation in maize crop was made post emergence of crop and weeds. Weeds were counted in 5 randomly selected record plots 0.06 m2 in size, analysis of weed botanical composition was done, the weeds were dried up to a dry weight and weighed [26]. Weed number was re-calculated into weeds m-2, dry matter weight into g m-2. Such assessment was conducted before each cut of living mulches and before maize harvesting. Soil contamination with weed seeds was estimated after maize harvesting. Soil samples were taken with a sampling auger in 10 places of the record plot from the 0–20 cm depth of the ploughlayer. The number of weed seeds found was re-calculated into thousand seeds m-2 [25]. The tests were done in 2009 and 2011.

**Photo 2.** Inter-seeded red clover.

plots in the same places. Living mulches were cut and chopped 2–3 times at maize growth stages BBCH 15–16, 31–32 and 63–65. BBCH 15–16 is leaf development stage when average maize height is 10–12 cm (Photo 1). BBCH 31–32 is stem elongation stage when 1–2 nodes are visible and maize height is 56–63 cm. BBCH 63–65 is maize flowering stage when the plant

Later the practice was abandoned since tractor-hitched implement would not be able to do this. Mulches were cut with a hand-operated brush cutter "Stihl" FS – 550, using a designed and manufactured trolley, reducing the operator's load, with a protection hood, which evenly spreads the mulch in the inter-row and protects the crop from mechanical damage. Living mulches were cut after they had reached a height of up to 20–25 cm. Green mass of the living mulches was spread in maize inter-rows. At stem elongation stage (BBCH 31–32), the maize crop was additionally fertilized with nitrogen (N60). When fertilizing at 250 kg N ha-1 rate, no significant differences were observed between maize cultivation systems. The objective of our experiment was to determine the competition among living mulches, maize and weeds; therefore the total nitrogen rate selected was as low as 108 kg N ha-1. Maize samples for the determination of productivity were hand-cut at the end of September – middle of October (BBCH 87–88) at maize physiological maturity stage. After harvesting, the remaining plant residues were ploughed in by a reversible plough with semi-helical mouldboards at the 20–22

A hybrid maize cultivar 'Silvestre' was used in our experiment. Gul et al. [30] have reported that a denser maize crop increased competition between maize and weeds. As a result, the seed rate of maize in our experiment was 130–138 thousand seeds ha-1 or (20–23 kg ha-1). Spring rape (cv. 'Sponsor'), white mustard (cv. 'Braco'), Italian ryegrass (cv. 'Avance'), black medic

height is 70–215 cm. At flowering stage, the living mulch was cut only in 2009.

**Photo 1.** After first cut of living mulch. 2009.

100 Weed Biology and Control

cm depth.

#### **3.1. Weed seed-bank in the soil**

Weed seed bank in the ploughlayer was established at the beginning of the experiment in 2009 and at the end in 2011 (Fig. 1-2). The seeds of *Chenopodium album* L. accounted for the largest share in the total weed seed bank. Analysis of the change in weed seed bank over the three experimental years suggested that living mulches reduced weed seed bank in the ploughlayer by 14.1 to 57.1 %. In 2011, compared with the control treatment, the lowest number of weeds was established when growing white mustard (8.0 %) and Persian clover (30.4 %) living mulches. Although weed suppressive capacity of Italian ryegrass was high, contrary to expectations, it gave only a small reduction in weed seed bank and the weeds were signifi‐ cantly, nearly twice as big as those in maize crop without living mulch.

Notes: C – control treatment (without living mulch), SR – spring rape, WM – white mustard, SB – spring barley, IR – Italian ryegrass, BM – black medic, PC – Persian clover, RC – red clover; differences significant at: \* – 95 % probability level, \*\* – 99 % probability level. Control – reference treatment when analyzing mass of living mulches – red clover living mulch.

**Figure 1.** The impact of living mulch on weed seed-bank in the soil, 2009

Notes: C – control treatment (without living mulch), SR – spring rape, WM – white mustard, SB – spring barley, IR – Italian ryegrass, BM – black medic, PC – Persian clover, RC – red clover; differences significant at: \* – 95 % probability level, \*\* – 99 % probability level. Control – reference treatment when analyzing mass of living mulches – red clover living mulch.

**Figure 2.** The impact of living mulch on weed seed-bank in the soil, 2011

#### **3.2. The abundance of weeds and living mulch**

155.9

77.9

57.9

95.8

164.5\*

135.1

206.6\*

191.6\*

168.7

*Chenopodium album Polygonum lapathifolium Sinapis arvensis Other weeds*

C SR WM SB IR BM PC RC Living mulch

Notes: C – control treatment (without living mulch), SR – spring rape, WM – white mustard, SB – spring barley, IR – Italian ryegrass, BM – black medic, PC – Persian clover, RC – red clover; differences significant at: \* – 95 % probability level, \*\* – 99 % probability level. Control – reference treatment when analyzing mass of living mulches – red clover

*Chenopodium album Polygonum lapathifolium*

102.2

*Echinochloa crus – galli Other weeds*

C SR WM SB IR BM PC RC Living mulch

Notes: C – control treatment (without living mulch), SR – spring rape, WM – white mustard, SB – spring barley, IR – Italian ryegrass, BM – black medic, PC – Persian clover, RC – red clover; differences significant at: \* – 95 % probability level, \*\* – 99 % probability level. Control – reference treatment when analyzing mass of living mulches – red clover

76.5

118.7

147.3

**Figure 1.** The impact of living mulch on weed seed-bank in the soil, 2009

121.5

**Figure 2.** The impact of living mulch on weed seed-bank in the soil, 2011

83.2

thousand m-2

0

living mulch.

50

100

150

200

77.9

thousand m-2

0

living mulch.

50

100

150

200

250

102 Weed Biology and Control

At early development stages of maize, more intensive growth was exhibited by spring rape, barley and white mustard living mulches (Table 14). However, living mulches of Italian ryegrass, black medic, Persian and red clover up to the first cut (maize BBCH 15–16) were only at seedling stage and therefore competed weakly with weeds. An especially rapid growth rate was shown by white mustard and until the first cut its dry mass was the highest. However, spring rape, barley and white mustard intercrops were sensitive to mulching and their regrowth after cut was poor, and in the second half of the summer they completely rotted away, the cut mass rapidly decomposed, therefore at later development stages of maize weed number and mass increased. Irrespective of this, these living mulches served their major purpose – competed with weeds at the time when maize competitive ability was low. The *Fabaceae* living mulches grown in maize inter-rows developed slowly; however, in the second half of the summer their growth rate increased and after cutting continued until the end of maize growing season. Moreover, they produced the largest mass. Compared with other *Fabaceae* family plants, black medic exhibited a slower development rate. Its mass was lower than that of other *Fabaceae* plants and it suppressed weeds more poorly; however, better than spring rape, barley and white mustard living mulches that had rotted away by the end of the summer. Italian ryegrass living mulch also produced large mass and exhibited a good weed suppressive ability. Its vegetation also continued until maize harvesting.



Notes: C – control treatment (without living mulch), SR – spring rape, WM – white mustard, SB – spring barley, IR – Italian ryegrass, BM – black medic, PC – Persian clover, RC – red clover; differences significant at: \* – 95 % probability level, \*\* – 99 % probability level. Control – reference treatment when analyzing mass of living mulches – red clover living mulch.

**Table 14.** The abundance of weeds and living mulch plants over the whole growing season of maize, 2009–2011

The correlation-regression analysis of the data from 2009 revealed statistically significant relationships between dry mass of living mulches and weed number and dry mass (Table 15).


Note: n–non-significant or weak relationship. \* – significant differences from control treatment (conventional plough‐ ing) at 95 % probability level, \*\* – at 99 % probability level.

**Table 15.** The relationships between dry mass of living mulches (*x*) and weed number and dry mass (*Y*) over the whole growing season of maize 2009–2011

#### **4. Conclusions**

**1.** In most cases, different tillage did not have significant impact on weed seed bank in the ploughlayer and weed abundance in the agricultural crops tested. The ploughlayer differentiated into the upper layer with a greater weed seed bank (60.1 % of the total weed seed bank) and bottom layer with a less abundant weed seed bank (39.9 %). In spring crops, weed mass in shallow-ploughed plots was by on average 28.6 %, in deep-cultivated plots by 41.5 %, in shallow-cultivated plots by 39.9 % and in not tilled crops by 16.1 % higher than that in conventionally ploughed plots, and in winter wheat crop by respec‐ tively 2.5; 2.3; 3.4 times higher, and in not tilled plots by 2.8 times lower.


#### **Author details**

**Living mulch**

104 Weed Biology and Control

living mulch.

**Growing season**

number m-2 mass

ing) at 95 % probability level, \*\* – at 99 % probability level.

growing season of maize 2009–2011

**4. Conclusions**

**Weeds**

**annual perennial total**

RC 409.5 174.3 6.2 4.0 415.7 178.3 272.2 2011 C 579.3 109.7 18.8 8.7 598.1 118.4 – SR 567.1 238.6\* 21.9 20.3\* 589.0 258.9 37.9\* WM 654.2 266.0\* 42.8\* 37.6\* 697.0\* 303.6\* 41.1\* SB 597.9 248.3\* 27.1 29.8\* 625.0 278.1\* 37.6 IR 437.6\* 126.0 9.4 2.2 447.0 148.2 220.9 BM 578.2 195.7 17.7 8.0 595.9 203.7 78.1\* PC 483.3 155.8 10.4 12.0 493.7 167.8 226.0 RC 443.3 203.3 2.1\* 0.9\* 445.4\* 204.2 166.8 Notes: C – control treatment (without living mulch), SR – spring rape, WM – white mustard, SB – spring barley, IR – Italian ryegrass, BM – black medic, PC – Persian clover, RC – red clover; differences significant at: \* – 95 % probability level, \*\* – 99 % probability level. Control – reference treatment when analyzing mass of living mulches – red clover

g m-2 number m-2 mass

g m-2

g m-2 number m-2 mass

**Table 14.** The abundance of weeds and living mulch plants over the whole growing season of maize, 2009–2011

The correlation-regression analysis of the data from 2009 revealed statistically significant relationships between dry mass of living mulches and weed number and dry mass (Table 15).

 0.916\*\* –0.797\* n n –0.908\*\* –0.796\* –0.762\* –0.948\*\* –0.909\*\* –0.850\*\* –0.820\* –0.956\*\* –0.802\* –0.778\* –0.949\*\* –0.731\* –0.802\* –0.726\* Note: n–non-significant or weak relationship. \* – significant differences from control treatment (conventional plough‐

**Table 15.** The relationships between dry mass of living mulches (*x*) and weed number and dry mass (*Y*) over the whole

**1.** In most cases, different tillage did not have significant impact on weed seed bank in the ploughlayer and weed abundance in the agricultural crops tested. The ploughlayer differentiated into the upper layer with a greater weed seed bank (60.1 % of the total weed seed bank) and bottom layer with a less abundant weed seed bank (39.9 %). In spring

**Weeds, Y annual perennial total** number m-2 g m-2 number m-2 g m-2 number m-2 g m-2

**Living mulch g m-2**

> Kęstutis Romaneckas1\*, Egidijus Šarauskis2 , Dovilė Avižienytė<sup>1</sup> and Aida Adamavičienė<sup>1</sup>

\*Address all correspondence to: kestas.romaneckas@asu.lt

1 Aleksandras Stulginskis University, Institute of Agroecosystems and Soil Sciences, Kaunas reg., Lithuania

2 Aleksandras Stulginskis University, Institute of Agricultural Engineering and Safety, Kaunas reg., Lithuania

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