**6. Green fertilization in "one-and-a-half-year sugarcane"**

As previously mentioned in item 4 (implantation of sugarcane plantation), one of the advantages of planting the "one-and-a-half-year sugarcane" is the possibility of a green fertilization prior to the planting of sugarcane. Among the main desirable characteristics of plants used for green fertilization are the following: the possibility of using mechanization from sowing to the harvesting of seeds, the ability to associate with nitrogen-fixing bacteria, rapid growth to control weeds, having mechanisms, or being able to synthesize compounds that help control pests (e.g., nematodes) and diseases, no dormant seeds, and a vigorous and deep root system that assists in the recycling of nutrients from the deepest layers and in soil decompaction. Another aspect to be considered is the supply of organic and mineral substrate to soil microorganisms. Thus, green fertilization also contributes to the improvement of the biological quality of the soil [2–4]. Several legumes have these characteristics, but there is generally a preference for *Crotalaria juncea* in South Central Brazil [1].

In the studies conducted by the authors of this chapter in the Zona da Mata region, green fertilization with *Crotalaria juncea* prior to planting the "one-and-ahalf-year sugarcane" resulted in increased yield in the plant-cane and first regrowth cycles, which together ranged from 20 to 26 t of culms per ha. In a multiyear analysis, the costs of green fertilization corresponded to 6–12 t of industrializable culms per ha. Thus, the increase in yields covered the costs of growing the legume. Furthermore, there are studies in which increased yields of sugarcane as a result of green fertilization with *Crotalaria juncea* were higher. For instance, in studies conducted over several years in the city of Sales Oliveira, state of São Paulo, Ref. [5] reported increased yields of industrializable culms ranging from 26 to 40 t per ha.

*Crotalaria juncea* exhibits high growth rates, which result in increased plant height, as shown in **Table 4**. High growth rate associated with increased plant


#### **Table 4.**

*Plant height, leaf area index (LAI), dry matter accumulation (DM accumulation), and dry matter accumulation rate (DM accumulation rate) in shoot biomass of Crotalaria juncea at 30, 45, 60, 75, 90, 105, and 120 days after plant emergence (DAE).*

height causes shading of the soil and affects other plants, especially weeds. This is one of the reasons it is used in weed control [1, 4]. Cultural methods are practices that aim to make the crop more competitive than weeds and include reducing planting space, intercropping or rotation with green manure.

Ref. [6] reported excellent results with the use of *Crotalaria juncea*, with weed control percentages greater than 90% in areas with a predominance of grasses, competitive plants, and high nutritional and photosynthetic efficiency. These results were confirmed by Ref. [3], who found that *Crotalaria juncea* was outstanding in terms of soil cover. Plants covered 100% of the soil 50 days after emergence, contributing to the control of erosion and weeds. In addition to the physical effect of shading, *Crotalaria juncea* releases organic compounds from its secondary metabolism (allelopathic compounds), which inhibit weed seed germination or slow down its development [2, 5–7]. Field observations by the authors confirm this allelopathic effect on weeds, verified by the absence of weeds between the planting rows (**Figure 3**). The sowing of *Crotalaria juncea* was carried out in an area adjacent to *Brachiaria* pasture. Therefore, the seed bank of this area should be large.

*Crotalaria juncea* is extremely sensitive to the length of night (nictoperiod), flowering early under increasing long nights and hence interrupting growth and reducing dry matter accumulation and nutrient cycling, especially of nitrogen [1, 7]. **Table 5** shows the accumulation of dry matter and nitrogen in shoot biomass of *Crotalaria juncea*, as well as plant height was statistically similar for the first three sowing times (beginning of October to beginning of November). For sowing times of mid-November, early and mid-December, there was an average percentage reduction in dry matter accumulation of around 20, 35, and 40% in comparison with the beginning of October.

These reductions were around 6, 13, and 24% for plant height in comparison with that of the first sowing times (**Table 5**). The study was conducted in a Latossolo vermelho amarelo distrófico, which exhibited the following chemical characteristics at 0–20 cm: pH in H2O = 6.2; 6.0 mg/dm3 of phosphorus and 59 mg/dm3 of potassium, (extracted with Mehlich), no exchangeable aluminum and 45% of base saturation. *Crotalaria juncea* is very sensitive to aluminum toxicity and when the soil has exchangeable aluminum, liming should be done prior to sowing [1, 4].

Due to the sensitivity of *Crotalaria juncea* to nictoperiod, the delay in sowing results in early flowering. The authors of this chapter have observed in crops of *Crotalaria juncea* of the Zona da Mata region that plants are able to receive the stimulus for floral induction around 40 days after emergence. Thus, for sowing times

#### **Figure 3.**

*Crotalaria juncea at the early growth stage and its allelopathic effect on weeds confirmed by the absence of weeds between the planting rows (photo on the right).*

**29**

*5%.*

**Table 5.**

*Sugarcane Production Systems in Small Rural Properties DOI: http://dx.doi.org/10.5772/intechopen.84975*

starting in mid-November, the nights will be increasing in length and early flowering will occur at around 40 days after emergence. The results of studies on sowing times carried out by the authors of this chapter and those found in literature allow us to conclude that to obtain high biomass production in shoots of *Crotalaria juncea*, the sowing of the legume in South Central Brazil should be done from the beginning from October to early November. The incorporation of *Crotalaria juncea* to the soil should be done when the first pods are in the phenological stage of grain filling, at which time

*Accumulation of dry matter (DM accumulation) and nitrogen (N accumulation) in shoot biomass of Crotalaria juncea, and plant height at the grain formation stage according to the sowing time in a study* 

*conducted during two agricultural years on a dystrophic red-yellow Latosol (Oxisol).*

**Sowing times DM accumulation N accumulation Plant height**

Early October 14,135 a 14,789 a 273 a 284 a 293 a 305 a Mid-October 14,768 a 14,845 a 297 a 275 a 311 a 298 a Early November 14,235 a 13,785 a 268 a 279 a 287a 293 a Mid-November 11,985 b 11,178 b 220 b 226 b 267 b 256 b Early December 9,123 c 9,545 c 198 bc 203 c 247 c 236 c Mid-December 8,523 d 8,037 d 174 c 168 d 217 d 208 d *Means followed by the same letter in the column do not differ statistically from one another other by the Tukey test at* 

**(kg/ha) (kg/ha) (cm) Year 1 Year 2 Year 1 Year 2 Year 1 Year 2**

The accumulation of nitrogen in the shoot biomass of *Crotalaria juncea* has also varied according to sowing time. **Table 5** shows that for sowing times from the beginning of October to the beginning of November, nitrogen accumulation in the shoot biomass of *Crotalaria juncea* oscillates around 300 kg/ha. Of the total nitrogen accumulated in the shoot biomass of *Crotalaria juncea*, about 60% originated from the symbiotic associations of the roots with N2 fixing bacteria, resulting in the contribution of significant amounts of N to the soil-plant system [4, 8] and greater sustainability of the subsequent crop. For comparative purposes, let us consider ammonium sulfate, which is one of the most commonly used nitrogen fertilizers. In 100 kg of ammonium sulfate, there is 20 kg of N. Therefore, it would be necessary

The inoculation of *Crotalaria juncea* seeds with nitrogen-fixing bacteria could be a way to increase N2 biological fixation and nitrogen supply in the soil-plant system. However, research conducted by the authors of this chapter in small farms located in the Zona da Mata region and at sugarcane mills showed that the inoculation of *Crotalaria juncea* seeds with nitrogen-fixing bacteria did not increase N supply in the soil-plant system. Similar results were obtained at EMBRAPA Agrobiologia by Ref. [9], who also found that the inoculants used were not more efficient than the native strains. There was no difference in dry matter and nitrogen accumulation among the treatments with and without inoculation. One of the possible causes could be the high native population of these bacteria in the soils. However, as mentioned by Ref. [10], the fact that the legumes present high nodulation with native strains does not mean that those bacteria have maximum efficiency, since many of these strains have a high competitive capacity, making it difficult to introduce other strains through seed inoculation. Thus, the authors believe that until more efficient and competitive strains are obtained, the

the accumulation of dry matter and nitrogen in shoots is the highest [1, 4, 7].

to use 1000 kg of ammonium sulfate to obtain 200 kg of N.


*Means followed by the same letter in the column do not differ statistically from one another other by the Tukey test at 5%.*

#### **Table 5.**

*Multifunctionality and Impacts of Organic and Conventional Agriculture*

ing space, intercropping or rotation with green manure.

with the beginning of October.

59 mg/dm3

sowing [1, 4].

height causes shading of the soil and affects other plants, especially weeds. This is one of the reasons it is used in weed control [1, 4]. Cultural methods are practices that aim to make the crop more competitive than weeds and include reducing plant-

Ref. [6] reported excellent results with the use of *Crotalaria juncea*, with weed control percentages greater than 90% in areas with a predominance of grasses, competitive plants, and high nutritional and photosynthetic efficiency. These results were confirmed by Ref. [3], who found that *Crotalaria juncea* was outstanding in terms of soil cover. Plants covered 100% of the soil 50 days after emergence, contributing to the control of erosion and weeds. In addition to the physical effect of shading, *Crotalaria juncea* releases organic compounds from its secondary metabolism (allelopathic compounds), which inhibit weed seed germination or slow down its development [2, 5–7]. Field observations by the authors confirm this allelopathic effect on weeds, verified by the absence of weeds between the planting rows (**Figure 3**). The sowing of *Crotalaria juncea* was carried out in an area adjacent

to *Brachiaria* pasture. Therefore, the seed bank of this area should be large.

*Crotalaria juncea* is extremely sensitive to the length of night (nictoperiod), flowering early under increasing long nights and hence interrupting growth and reducing dry matter accumulation and nutrient cycling, especially of nitrogen [1, 7]. **Table 5** shows the accumulation of dry matter and nitrogen in shoot biomass of *Crotalaria juncea*, as well as plant height was statistically similar for the first three sowing times (beginning of October to beginning of November). For sowing times of mid-November, early and mid-December, there was an average percentage reduction in dry matter accumulation of around 20, 35, and 40% in comparison

These reductions were around 6, 13, and 24% for plant height in comparison

and 45% of base saturation. *Crotalaria juncea* is very sensitive to aluminum toxicity and when the soil has exchangeable aluminum, liming should be done prior to

Due to the sensitivity of *Crotalaria juncea* to nictoperiod, the delay in sowing results in early flowering. The authors of this chapter have observed in crops of *Crotalaria juncea* of the Zona da Mata region that plants are able to receive the stimulus for floral induction around 40 days after emergence. Thus, for sowing times

*Crotalaria juncea at the early growth stage and its allelopathic effect on weeds confirmed by the absence of* 

of potassium, (extracted with Mehlich), no exchangeable aluminum

of phosphorus and

with that of the first sowing times (**Table 5**). The study was conducted in a Latossolo vermelho amarelo distrófico, which exhibited the following chemi-

cal characteristics at 0–20 cm: pH in H2O = 6.2; 6.0 mg/dm3

**28**

**Figure 3.**

*weeds between the planting rows (photo on the right).*

*Accumulation of dry matter (DM accumulation) and nitrogen (N accumulation) in shoot biomass of Crotalaria juncea, and plant height at the grain formation stage according to the sowing time in a study conducted during two agricultural years on a dystrophic red-yellow Latosol (Oxisol).*

starting in mid-November, the nights will be increasing in length and early flowering will occur at around 40 days after emergence. The results of studies on sowing times carried out by the authors of this chapter and those found in literature allow us to conclude that to obtain high biomass production in shoots of *Crotalaria juncea*, the sowing of the legume in South Central Brazil should be done from the beginning from October to early November. The incorporation of *Crotalaria juncea* to the soil should be done when the first pods are in the phenological stage of grain filling, at which time the accumulation of dry matter and nitrogen in shoots is the highest [1, 4, 7].

The accumulation of nitrogen in the shoot biomass of *Crotalaria juncea* has also varied according to sowing time. **Table 5** shows that for sowing times from the beginning of October to the beginning of November, nitrogen accumulation in the shoot biomass of *Crotalaria juncea* oscillates around 300 kg/ha. Of the total nitrogen accumulated in the shoot biomass of *Crotalaria juncea*, about 60% originated from the symbiotic associations of the roots with N2 fixing bacteria, resulting in the contribution of significant amounts of N to the soil-plant system [4, 8] and greater sustainability of the subsequent crop. For comparative purposes, let us consider ammonium sulfate, which is one of the most commonly used nitrogen fertilizers. In 100 kg of ammonium sulfate, there is 20 kg of N. Therefore, it would be necessary to use 1000 kg of ammonium sulfate to obtain 200 kg of N.

The inoculation of *Crotalaria juncea* seeds with nitrogen-fixing bacteria could be a way to increase N2 biological fixation and nitrogen supply in the soil-plant system. However, research conducted by the authors of this chapter in small farms located in the Zona da Mata region and at sugarcane mills showed that the inoculation of *Crotalaria juncea* seeds with nitrogen-fixing bacteria did not increase N supply in the soil-plant system. Similar results were obtained at EMBRAPA Agrobiologia by Ref. [9], who also found that the inoculants used were not more efficient than the native strains. There was no difference in dry matter and nitrogen accumulation among the treatments with and without inoculation. One of the possible causes could be the high native population of these bacteria in the soils. However, as mentioned by Ref. [10], the fact that the legumes present high nodulation with native strains does not mean that those bacteria have maximum efficiency, since many of these strains have a high competitive capacity, making it difficult to introduce other strains through seed inoculation. Thus, the authors believe that until more efficient and competitive strains are obtained, the

inoculation of the seeds of *Crotalaria juncea* will not result in increased nitrogen biological fixation and accumulation by the plant.
