**3. Potassium as a water-stress ameliorative agent**

sult of root length density variability, increased with the soil profile depth. The degree of nitrate's utilization by wheat was the highest in the top-soil, several times exceeding its po‐ tential to deliver the required amount of nitrogen. The most spectacular is the fact that in the 7th-day period, the depletion of the nitrate-nitrogen zone extended down to 150 cm. At the same time, the K depletion zone occurred at the depth of 60 cm. In the case of sugar beet, the depletion zone for nitrates reached down to 90 cm, whereas for potassium only to 30 cm.

**Winter wheat 1 Sugar beet2**

**cm · cm-3**

**NO3 - K+ NO3 - K+**

r1 **cm**

2.7 0.73 509 134

**Dd, %**

**Dd, % Lvr**

10-20 3.1 0.68 546 144 20-30 2.1 0.83 449 118 30-60 1.7 0.92 404 106 0.38 1.95 191 50 60-90 1.0 1.20 310 82 0.26 2.35 158 42 90-120 0.7 1.43 259 68 0.08 4.24 88 23 120-150 0.27 2.31 161 42 0.01 12.00 31 8 150-190 0.03 6.93 54 14 - - - -

**Table 2.** Effect of root length density distribution in the soil profile on the degree of potassium and nitrate-nitrogen

These two sets of data outline some important information concerning the management of both nutrients. Firstly, at the critical period of each crop development, nitrogen should be considered as a nutrient significantly limiting plant growth. In the case of wheat as a crop accumulating a significant amount of nitrogen in grain, an external supply of this nutrient is required at heading to fulfill this goal. A quite different strategy should be recommended for sugar beet, since it reaches at the critical stage of K accumulation maximum rates of both dry matter and nitrogen accumulation [26, 37]. This crop in subsequent stages of growth re‐ lies on soil N resources, which uptake is governed by K supply. The second information re‐ fers to un-depleted resources of potassium, present in deeper soil layers. These reserves can be considered as the basic source of K supply during critical stages of beet growth and/or during any kind of growth disturbance due to stress. It is worth mentioning, that water shortages first limit nutrient flow in the topsoil, and then extend down the soil profile. Therefore, soil K reserves present in deeper soil layers are important for the exploitation of

The effective transformation of solar energy into plant biomass depends on the supply of nitro‐ gen, which is crucial for both carbon fixation and its subsequent partitioning among plant or‐

**Depth**

144 Soil Fertility

0-10

**Lvr cm · cm-3**

Adapted from 1[36] and 2[28]

**r1 cm**

8.2 0.42 888 234

depletion at the critical stage of potassium accumulation by two crops

the plant yielding potential or to protect its growth under stress.

## **3.1. Plant growth stages – Yield forming function of potassium**

Yield can be defined as the end-product of yield component's expression of a particular crop during growth and development. According to the concept *multiple limitation hypothesis* [MLH, 17], water and nitrogen supply plays a decisive role in assimilates partitioning among main crop plant organs [40, 41, 42]. These two nutrients affect both the rate of dry matter accumulation and yield component's development. In order to understand their in‐ fluence on the rate of dry matter accumulation of the yield, the whole life cycle of a crop can be divided into three main periods: i) yield foundation (YFP), ii) yield construction (YCP), iii) yield realization (YRP) [43]. The shortage of potassium can affect plant growth in each of the above indicated periods. The key problem remains, about how potassium improves yield forming effect of water and nitrogen?

Potassium concentration in plant biomass varies from 1 to 5% of dry matter weight. When soil potassium is deficient, plant growth is reduced, resulting in smaller, dull bluish-green and wavy leaves and thinner stems. Plants often tend to wilt. Visual symptoms of potassium deficiency are easily recognized, but only those under severe potassium shortage, (Photo 1). In early stages of growth and also under hidden K deficiency, its visible symptoms are even‐ tually confused with nitrogen deficiency. The main reason is the slow rate of the aerial bio‐ mass growth. The shortage of potassium is the reason of basic physiological processes disturbance, which in turn negatively affect the development of yield components. Potassi‐ um deficient plants: a) develop a weak root system, b) are not efficient in nitrogen uptake, c) grow slowly, d) develop infirm stems and lodges frequently, e) use inefficiently water and nitrogen, f) show high susceptibility to diseases, g) yield miserably, h) produce lower quali‐ ty yield [19, 20]. The recent study conducted in Canada showed that the shortage of potassi‐ um reduces grain of maize by 13% [44]. In the Central-Eastern European countries, during the last two decades, the supply of nitrogen has not been balanced with potassium and phosphorus, in turn seriously limiting harvested yields of cereals [45].

**Crop** Visual symptoms of deficiency negatively responded component/parts

**Table 3.** Effect of potassium deficiency during the linear period of crops growth on visual symptoms and yield

**Level of factor Yield and elements of yield structure**


http://dx.doi.org/10.5772/53185

147


Sustainable Management of Soil Potassium – A Crop Rotation Oriented Concept





**Yield, t ha-1 NKR3 NKC TGW, g L1 M2 L M L M L M**

NP 6.49 a 8.27 a 24.9 a 26.8 a 357 a 390 a 239 a 259 a

NPK 7.05 b 9.61 b 26.3 a 29.2 b 376 a 421 b 251 ab 284 b

NPKMgS 7.46 b 10.1 b 26.3 a 29.1 b 370 ab 411 ab 261 b 306 c

NPKMgSNa 7.35 b 10.6 c 24.6 a 27.7 ab 365 ab 405 ab 249 ab 323 d

2006 2.73 a 8.13 a 14.3 a 25.7 a 159 a 334 a 217 a 298 b

2007 9.69 c 10.5 b 30.6 b 31.9 b 470 b 476 c 259 b 277 a

Years 2005 8.85 b 10.3 b 31.7 b 27.0 a 473 b 410 b 275 c 301 b

**Table 4.** Statistical evaluation of main factors affecting yield and structural components of maize grain yield at the


**Cereals** dull green color; tip and marginal chlorosis on

tan-coloring of lower leaves

**Sugar beet** early leaves wilting during heat of the mid-

**Potato** wilting-like shape of canopy during heat of

marginal chlorosis on lower leaves

day, tip and marginal chlorosis on older leaves

the mid-day, tip and marginal chlorosis on

means with the same letter are not significantly different at α=0.05 (Tukey test); 1L: light soil - loamy sand, 2M: medium soil - sandy loam; 2NR - number of rows per cob,

NKR – number of kernels per row, NKC – number of kernels per cob, TGW – thousand grain weight.

**Maize** curling of leaves by mid-morning, tip and

lower leaves

**Oil-seed rape** smaller rate of rosette growth,

older leaves

components development

**Experimental factor**

Fertilizing treatments

Source [55]

background of soils differing in texture

a

In the yield foundation period (YFP), K supply affects both the root system and aerial parts build up. In cereals, it stops at the end of tillering, and in all dicotyledonous crops, at the rosette stage. In general, at the beginning of the plant life cycle, the supply of water and nutrient is not consid‐ ered as the factor limiting the root system extension. As a rule, all nutrients are uniformly distrib‐ uted, and roots follow the genetically fixed patterns [30, 46]. Plants grown in soil fertilized with potassium, i.e., in the K fertile soil, show at early stages much higher rate of root system in‐ growths. As a result, roots of plants well supplied with K are able to reach the deeper soil layers considerably earlier, than those poorly K-nourished. For example, the daily rate of extension of sugar beet roots, due to ample K supply can be accelerated by 50% as compared to plants grown in the K medium K level, irrespectively of the weather course. The same degree of maize re‐ sponse to high K availability has been documented. Cereals, for instance spring barley showed a much weaker response to the elevated K soil level [47]. The observed phenomenon supports the hypothesis, that K induces adaptation of crops to summer semi-drought, which emerges irregu‐ larly in temperate regions.

The key attribute of the yield construction period (YCP) is the linear rate of the dry matter in‐ crease. At the end of this period, crop plants reach the highest rate of growth. Therefore, K sup‐ ply during this particular period is considered as the critical factor of yield performance. In cereals, it extends from the end of tillering up to the end of heading [48]. In other seed crops, the most sensitive phase to K shortage extends from the rosette up to the budding. Vegetable crops show sensitivity to K supply from the rosette up to technological maturity. For high-yielding crops, K supply is crucial for maximizing the dry matter accumulation and critical for yield com‐ ponent's development (Table 3). For example in maize, the shortage of potassium during anthe‐ sis negatively affects the number of kernels on the cob [49, 50]. As shown in Table 4, plants grown on light soil showed poor development of this yield component, mainly due to the extremely strong response to drought in 2006. Therefore, any shortage of K during the linear period of each plant growth is considered as critical for final yield development.

The yield realization period (YRP) of a particular crop extends from the beginning of anthesis up to final maturity. The shortage of K affects the most vegetable crops, including potatoes. Seed crops are also sensitive to K supply during ripening, especially in regions of year-to-year weath‐ er variability. For example, the content of potassium in the flag leaf of winter wheat at the stage of milk grain maturity can significantly affect the yield (Y), as presented by the equation [51]:

$$\text{If } \mathbf{Y} = 2.35\mathbf{K} + 4.0; \mathbf{R}^2 = 0.75 \text{ n} = 9 \text{ and } \mathbf{P} \le 0.01 \tag{7}$$


**Table 3.** Effect of potassium deficiency during the linear period of crops growth on visual symptoms and yield components development


#### Source [55]

um deficient plants: a) develop a weak root system, b) are not efficient in nitrogen uptake, c) grow slowly, d) develop infirm stems and lodges frequently, e) use inefficiently water and nitrogen, f) show high susceptibility to diseases, g) yield miserably, h) produce lower quali‐ ty yield [19, 20]. The recent study conducted in Canada showed that the shortage of potassi‐ um reduces grain of maize by 13% [44]. In the Central-Eastern European countries, during the last two decades, the supply of nitrogen has not been balanced with potassium and

In the yield foundation period (YFP), K supply affects both the root system and aerial parts build up. In cereals, it stops at the end of tillering, and in all dicotyledonous crops, at the rosette stage. In general, at the beginning of the plant life cycle, the supply of water and nutrient is not consid‐ ered as the factor limiting the root system extension. As a rule, all nutrients are uniformly distrib‐ uted, and roots follow the genetically fixed patterns [30, 46]. Plants grown in soil fertilized with potassium, i.e., in the K fertile soil, show at early stages much higher rate of root system in‐ growths. As a result, roots of plants well supplied with K are able to reach the deeper soil layers considerably earlier, than those poorly K-nourished. For example, the daily rate of extension of sugar beet roots, due to ample K supply can be accelerated by 50% as compared to plants grown in the K medium K level, irrespectively of the weather course. The same degree of maize re‐ sponse to high K availability has been documented. Cereals, for instance spring barley showed a much weaker response to the elevated K soil level [47]. The observed phenomenon supports the hypothesis, that K induces adaptation of crops to summer semi-drought, which emerges irregu‐

The key attribute of the yield construction period (YCP) is the linear rate of the dry matter in‐ crease. At the end of this period, crop plants reach the highest rate of growth. Therefore, K sup‐ ply during this particular period is considered as the critical factor of yield performance. In cereals, it extends from the end of tillering up to the end of heading [48]. In other seed crops, the most sensitive phase to K shortage extends from the rosette up to the budding. Vegetable crops show sensitivity to K supply from the rosette up to technological maturity. For high-yielding crops, K supply is crucial for maximizing the dry matter accumulation and critical for yield com‐ ponent's development (Table 3). For example in maize, the shortage of potassium during anthe‐ sis negatively affects the number of kernels on the cob [49, 50]. As shown in Table 4, plants grown on light soil showed poor development of this yield component, mainly due to the extremely strong response to drought in 2006. Therefore, any shortage of K during the linear period of each

The yield realization period (YRP) of a particular crop extends from the beginning of anthesis up to final maturity. The shortage of K affects the most vegetable crops, including potatoes. Seed crops are also sensitive to K supply during ripening, especially in regions of year-to-year weath‐ er variability. For example, the content of potassium in the flag leaf of winter wheat at the stage of milk grain maturity can significantly affect the yield (Y), as presented by the equation [51]:

<sup>2</sup> Y = 2.35K + 4.0; R = 0.75 n = 9 and P 0.01 £ (7)

phosphorus, in turn seriously limiting harvested yields of cereals [45].

plant growth is considered as critical for final yield development.

larly in temperate regions.

146 Soil Fertility

a means with the same letter are not significantly different at α=0.05 (Tukey test);

1L: light soil - loamy sand, 2M: medium soil - sandy loam; 2NR - number of rows per cob,

NKR – number of kernels per row, NKC – number of kernels per cob, TGW – thousand grain weight.

**Table 4.** Statistical evaluation of main factors affecting yield and structural components of maize grain yield at the background of soils differing in texture

This finding corroborates the importance of the subsoil K reserves for efficient manage‐ ment of N, as the nutrient decisive for leaves activity during ripening of cereals. The grain weight increase in response to K supply is probably related to its effect on assim‐ ilates transportation in the phloem [20]. Thousand-grain weight (TGW), a structural pa‐ rameter of a grain yield of seed crops, indirectly describes a plant nutritional status in this period. The final weight of kernels generally reflects the crop canopy capability both to produce and to supply carbohydrates to growing kernels [52]. As presented in Table 4, this yield component showed a significant response to all studied factors, but the soil complex was the most important. Plants grown on soil, naturally reach in po‐ tassium, achieved TGW by 17% higher as compared to those grown on light soil, in spite of the same content of K initially available.

consequence root system may be less able to utilize reserves of water stored in deeper

Sustainable Management of Soil Potassium – A Crop Rotation Oriented Concept

http://dx.doi.org/10.5772/53185

149

The main agronomic problem, but not only, is the question how the water deficit may be ameliorated? In agriculture practice irrigation and breeding used to be treated as the main ways for overcoming water shortages. The simplest solution is to supply more water, i.e., to irrigate. However, not all farmers can invest in irrigation equip‐ ments. The second solution is to find out varieties, well adapted to water shortage. So far, in spite of huge investigation, breeding for drought resistance, remains still the open-box [56, 57]. It is well known, that root morphology is guided genetically, but the ultimate shape of the root system largely depends on the effects of environmental fac‐ tors. The depth of the soil reservoir that holds water available to a plant is, in fact, de‐ termined by plant's rooting, in turn depending on soil characteristics, including compacted layers and water storage. Hence, the extension of roots into deep soil layers is crucial for crop performance under limited water supply. Drought adapted plants are characterized by great and vigorous root systems [58]. Experimental studies con‐ ducted in England showed that winter wheat roots below 1 m contribute only to 3% of total root system weight, but at the same time it delivered 20% of the transpired

Under field conditions, water availability and its supply to currently growing crops is year-to-year variable, in turn affecting seasonal yields variability. Therefore, yields har‐ vested by farmers in *good years*, i.e., under relatively ample supply of water, are usually higher, expressing higher unit productivity of the applied nitrogen and *vice versa.* It is recognized, that plant growth is better maintained under stress if adequate amounts of nutrients are available throughout the growing season. The deficit of nutrients reduces the rate of metabolic processes in the plant, making energy transfer and other growth processes less efficient. The adequate, balanced supply of N, P, and K should meet crop requirements, keeping its healthy and vigorously throughout the growth season [19, 30, 33]. This conclusion is corroborated by data presented in Table 4. In 2005 and 2007, fa‐ vorable for maize growth, yields of plants fertilized with NPK were significantly higher compared with those fertilized only with NP, irrespectively on soil texture. In the ex‐ tremely dry 2006 year, in spite of the same input of fertilizers and soil K fertility level,

loamy sand and sandy loam. Grain yield responded to applied nutrients, but it was non-significant on the light soil (Fig. 5). This example implicitly indicates on the impor‐ tance of inherent soil K fertility in ameliorating water shortage, significantly affecting crop growth during the Yield Foundation Period (Table 4). It can be therefore conclud‐ ed that on light soils (L), K application ameliorates mild but not severe stresses. Soil or‐ iginated from loams (medium soils, M) are much more resistant to drought, allowing to

take under control water stress, provided a well potassium management.

/3 and ¼ lower as compared to good years, respectively for

soil layers [38, 46, 56].

water during dry periods [54].

harvested yields were by 2

Water requirements of plant crops are variable accordingly to the stage of their growth. The most sensitive stages cover the linear phase of biomass accumulation [see equation No. 7]. Sugar beet and potato plants are responsive to water supply during the most of the season, but especially during the highest rate of the dry matter increase, i.e., in the mid-season (July and August in the temperate regions of the world). Soil water capaci‐ ty is a function of its textural class and precipitation over the whole season. It has been documented, that long-term fertilization with potassium results in increasing content of plant available water [47]. This phenomenon is probably explained by specific, glue-like action of potassium ions to individual soil grains [53]. The spatial pattern of water up‐ take from various regions of the soil profile depends on both soil moisture and roots distribution [46]. Water uptake and extraction patterns are related to rooting density. For example, a high-yielding winter wheat extracts 50 to 60% of total water from the first 0.3 m; 20 to 25% from the second 0.3 m; 10 to 15% from the third 0.3 m and less than 10% from the fourth 0.3 m soil depth. The usability of water by plant root from deeper layers depends on its penetration ability [54]. However, the deepest parts of the soil profile are responsible for water and nitrogen supply during stages of maximum dry matter accumulation.

The maximum rate of water use by crop occurs at field capacity, i.e. at maximum soil available water content. As the soil dries, the attainable soil water content decreases, leading to a significant drop in plant water potential, which also depends on plant structure and transpiration rate. At the onset and during sustained periods of drought, highly synchronized responses occur between root and shoot tissues. Signals from the roots have almost immediate effects upon shoot growth and its physiological functions, which modify the crop plant response to drought, in turn its productivity. The pro‐ longed drought disturbs the diurnal rhythm of stomata, which are not able to control water loss from the leaves, further increasing the stress. Next, photosynthesis rate de‐ clines and respiration tend to increase, reducing consequently, dry matter accumulation. Shortage of assimilates transport to roots decreases the rate of their growth and as a consequence root system may be less able to utilize reserves of water stored in deeper soil layers [38, 46, 56].

This finding corroborates the importance of the subsoil K reserves for efficient manage‐ ment of N, as the nutrient decisive for leaves activity during ripening of cereals. The grain weight increase in response to K supply is probably related to its effect on assim‐ ilates transportation in the phloem [20]. Thousand-grain weight (TGW), a structural pa‐ rameter of a grain yield of seed crops, indirectly describes a plant nutritional status in this period. The final weight of kernels generally reflects the crop canopy capability both to produce and to supply carbohydrates to growing kernels [52]. As presented in Table 4, this yield component showed a significant response to all studied factors, but the soil complex was the most important. Plants grown on soil, naturally reach in po‐ tassium, achieved TGW by 17% higher as compared to those grown on light soil, in

Water requirements of plant crops are variable accordingly to the stage of their growth. The most sensitive stages cover the linear phase of biomass accumulation [see equation No. 7]. Sugar beet and potato plants are responsive to water supply during the most of the season, but especially during the highest rate of the dry matter increase, i.e., in the mid-season (July and August in the temperate regions of the world). Soil water capaci‐ ty is a function of its textural class and precipitation over the whole season. It has been documented, that long-term fertilization with potassium results in increasing content of plant available water [47]. This phenomenon is probably explained by specific, glue-like action of potassium ions to individual soil grains [53]. The spatial pattern of water up‐ take from various regions of the soil profile depends on both soil moisture and roots distribution [46]. Water uptake and extraction patterns are related to rooting density. For example, a high-yielding winter wheat extracts 50 to 60% of total water from the first 0.3 m; 20 to 25% from the second 0.3 m; 10 to 15% from the third 0.3 m and less than 10% from the fourth 0.3 m soil depth. The usability of water by plant root from deeper layers depends on its penetration ability [54]. However, the deepest parts of the soil profile are responsible for water and nitrogen supply during stages of maximum

The maximum rate of water use by crop occurs at field capacity, i.e. at maximum soil available water content. As the soil dries, the attainable soil water content decreases, leading to a significant drop in plant water potential, which also depends on plant structure and transpiration rate. At the onset and during sustained periods of drought, highly synchronized responses occur between root and shoot tissues. Signals from the roots have almost immediate effects upon shoot growth and its physiological functions, which modify the crop plant response to drought, in turn its productivity. The pro‐ longed drought disturbs the diurnal rhythm of stomata, which are not able to control water loss from the leaves, further increasing the stress. Next, photosynthesis rate de‐ clines and respiration tend to increase, reducing consequently, dry matter accumulation. Shortage of assimilates transport to roots decreases the rate of their growth and as a

spite of the same content of K initially available.

dry matter accumulation.

148 Soil Fertility

The main agronomic problem, but not only, is the question how the water deficit may be ameliorated? In agriculture practice irrigation and breeding used to be treated as the main ways for overcoming water shortages. The simplest solution is to supply more water, i.e., to irrigate. However, not all farmers can invest in irrigation equip‐ ments. The second solution is to find out varieties, well adapted to water shortage. So far, in spite of huge investigation, breeding for drought resistance, remains still the open-box [56, 57]. It is well known, that root morphology is guided genetically, but the ultimate shape of the root system largely depends on the effects of environmental fac‐ tors. The depth of the soil reservoir that holds water available to a plant is, in fact, de‐ termined by plant's rooting, in turn depending on soil characteristics, including compacted layers and water storage. Hence, the extension of roots into deep soil layers is crucial for crop performance under limited water supply. Drought adapted plants are characterized by great and vigorous root systems [58]. Experimental studies con‐ ducted in England showed that winter wheat roots below 1 m contribute only to 3% of total root system weight, but at the same time it delivered 20% of the transpired water during dry periods [54].

Under field conditions, water availability and its supply to currently growing crops is year-to-year variable, in turn affecting seasonal yields variability. Therefore, yields har‐ vested by farmers in *good years*, i.e., under relatively ample supply of water, are usually higher, expressing higher unit productivity of the applied nitrogen and *vice versa.* It is recognized, that plant growth is better maintained under stress if adequate amounts of nutrients are available throughout the growing season. The deficit of nutrients reduces the rate of metabolic processes in the plant, making energy transfer and other growth processes less efficient. The adequate, balanced supply of N, P, and K should meet crop requirements, keeping its healthy and vigorously throughout the growth season [19, 30, 33]. This conclusion is corroborated by data presented in Table 4. In 2005 and 2007, fa‐ vorable for maize growth, yields of plants fertilized with NPK were significantly higher compared with those fertilized only with NP, irrespectively on soil texture. In the ex‐ tremely dry 2006 year, in spite of the same input of fertilizers and soil K fertility level, harvested yields were by 2 /3 and ¼ lower as compared to good years, respectively for loamy sand and sandy loam. Grain yield responded to applied nutrients, but it was non-significant on the light soil (Fig. 5). This example implicitly indicates on the impor‐ tance of inherent soil K fertility in ameliorating water shortage, significantly affecting crop growth during the Yield Foundation Period (Table 4). It can be therefore conclud‐ ed that on light soils (L), K application ameliorates mild but not severe stresses. Soil or‐ iginated from loams (medium soils, M) are much more resistant to drought, allowing to take under control water stress, provided a well potassium management.

a

from [62]


4

6

treatments; 100, 140, 180 kg N ha-1.

Fig. 5. Response of maize grown on soils differing in texture to increased fertilization level in 2006 (dry year); Source [55] a means with the same letter are not significantly different at α=0.05 (Tukey test).

**Figure 5.** Response of maize grown on soil differing in texture to increased fertilization level in 2006 (dry year); Source [55]

means with the same letter are not significantly different at α=0.05 (Tukey test).

#### 16 **3.2. Impact of potassium on WUE – Maize as a case study**

8 10 12 14 yield of grain, t ha-1 The water-management index describing water-use efficiency (WUE) refers to the quantity of biomass produced by a crop plant per volume of water transpired and evaporated during its life cycle. In agronomy, the WUE index termed as the crop water productivity (CWP) re‐ lates the quantity of actually harvestable or marketable crop plant part (seeds, grain, roots, tubers, etc.) produced on a given area in a fixed period of time (yield, Y) per unit of tran‐ spired water [59]:

$$\text{CWP} = \text{Y}\_{\text{a}} / \text{ET}\_{\text{a}} \tag{8}$$

7

YG/L

2006 and 2007, with respect to the weather course, amounted to 622 and 572 m3

ing yielding effects of agronomic factors is limited.

ure on WUE, resulting in yield gain or loss.

for the water limited yield (WLY) calculation is as follows:

(see Table 4). However, in 2006, harvested yields on light soil were much lower than on the medium one (Fig. 5). In contrast in 2007 yields were both considerably higher and did not show dependence on soil texture. Therefore, the applicability of the CWP index for evaluat‐

The French and Schulz approach, expressed as the water limited yield concept (WLYC), [60] is proposed [60] for the description of the impact of K on water management. The algorithm

where: TE, maximum unit water productivity, fixed at the level of 20 kg ha-1 mm-1, R refers to the sum of rainfall during the growth period, WR expresses water reserves in the soil pro‐

The proposed procedure takes into account two variables affecting WUE, resulting in yield fractionation. The first yield fraction (WLY), reflects a maximum yield at a given amount of attainable water to a crop during its growth. Controversies about the applicability of the Eq. No 9 refer mostly to the threshold value of the TE, which was originally set up for wheat at the level of 20 kg of grain per 1 mm of water [61]. In maize, taking into account its higher water-use efficiency, this threshold value is questionable and should be fixed at a slightly higher level. The another controversy refers to the importance of water reserves, WR, present in the soil profile. This water reservoir is responsible for both water, and nutrients supply at early stages of a plant growth. Therefore, this component of soil water characteris‐ tic has been introduced by Authors (the current chapter) into the original French and Schulz equation. The second yield fraction quantifies the net effect of the applied agronomic meas‐

The graphical interpretation of the WLY concept, as proposed by Authors, allows to dis‐ criminate the effects resulting from the action of transpired water and that of the tested fac‐ tor. As shown in Fig. 6, the maximum yield of maize was higher in the favorable year 2001 as compared to the dry one, i.e., 2003. The effect of increasing nitrogen rates was dependent on potassium management. In the treatment without K application, the highest yield in‐ crease due to N was documented for its rate of 100 kg ha-1. In contrast, on plots with current K application, the highest yields were harvested in the treatment with 140 kg N ha-1, irre‐ spectively of the season. The relative contribution of K application in the final yield, meas‐ ured for this particular treatment, was 40% and 6% in 2001 and 2003, respectively. It can be therefore concluded, that the exploitation of maize potential significantly depends on the ni‐ trogen rate, but adjusted for the K fertility level. Therefore, any inadequately recommended N rate can result in yield decrease in good years or even its depression in years with

drought, as occurred in 2003 (Fig. 6) and in 2006 on the light soil (Fig. 5).

file down to 1 m, and ΣEs, represents the seasonal soil evaporation, equals to 110 mm.

WLY = TE (R + WR - ΣEs) (9)

Sustainable Management of Soil Potassium – A Crop Rotation Oriented Concept

, respectively

151

http://dx.doi.org/10.5772/53185


Fig. 6. Effect of soil K fertility level on maize yield in two weather contrastive years; Adapted

2001 2003 years and fertilizing treatments

Legend: WLY – water limited yield; YG/YL – yield loss/gain, K-, K+ - K fertilizing

2006 and 2007, with respect to the weather course, amounted to 622 and 572 m3 , respectively (see Table 4). However, in 2006, harvested yields on light soil were much lower than on the medium one (Fig. 5). In contrast in 2007 yields were both considerably higher and did not show dependence on soil texture. Therefore, the applicability of the CWP index for evaluat‐ ing yielding effects of agronomic factors is limited.

The French and Schulz approach, expressed as the water limited yield concept (WLYC), [60] is proposed [60] for the description of the impact of K on water management. The algorithm for the water limited yield (WLY) calculation is as follows:

$$\text{WLI} \,\text{Y} = \text{TE} \left( \text{R} + \text{WR} \cdot \text{E} \,\text{E}\_{\text{s}} \right) \tag{9}$$

where: TE, maximum unit water productivity, fixed at the level of 20 kg ha-1 mm-1, R refers to the sum of rainfall during the growth period, WR expresses water reserves in the soil pro‐ file down to 1 m, and ΣEs, represents the seasonal soil evaporation, equals to 110 mm.

The proposed procedure takes into account two variables affecting WUE, resulting in yield fractionation. The first yield fraction (WLY), reflects a maximum yield at a given amount of attainable water to a crop during its growth. Controversies about the applicability of the Eq. No 9 refer mostly to the threshold value of the TE, which was originally set up for wheat at the level of 20 kg of grain per 1 mm of water [61]. In maize, taking into account its higher water-use efficiency, this threshold value is questionable and should be fixed at a slightly higher level. The another controversy refers to the importance of water reserves, WR, present in the soil profile. This water reservoir is responsible for both water, and nutrients supply at early stages of a plant growth. Therefore, this component of soil water characteris‐ tic has been introduced by Authors (the current chapter) into the original French and Schulz equation. The second yield fraction quantifies the net effect of the applied agronomic meas‐ ure on WUE, resulting in yield gain or loss.

The graphical interpretation of the WLY concept, as proposed by Authors, allows to dis‐ criminate the effects resulting from the action of transpired water and that of the tested fac‐ tor. As shown in Fig. 6, the maximum yield of maize was higher in the favorable year 2001 as compared to the dry one, i.e., 2003. The effect of increasing nitrogen rates was dependent on potassium management. In the treatment without K application, the highest yield in‐ crease due to N was documented for its rate of 100 kg ha-1. In contrast, on plots with current K application, the highest yields were harvested in the treatment with 140 kg N ha-1, irre‐ spectively of the season. The relative contribution of K application in the final yield, meas‐ ured for this particular treatment, was 40% and 6% in 2001 and 2003, respectively. It can be therefore concluded, that the exploitation of maize potential significantly depends on the ni‐ trogen rate, but adjusted for the K fertility level. Therefore, any inadequately recommended N rate can result in yield decrease in good years or even its depression in years with drought, as occurred in 2003 (Fig. 6) and in 2006 on the light soil (Fig. 5).

7

YG/L WLY

Fig. 5. Response of maize grown on soils differing in texture to increased fertilization level in

NP. NPK NPKMg NPKMgNa NP. NPK NPKMg NPKMgNa loamy sand, L sandy loam, M soil textural class, fertilizing treatments

a

<sup>b</sup> <sup>b</sup>

c

a

Fig. 6. Effect of soil K fertility level on maize yield in two weather contrastive years; Adapted

100 140 180 100 140 180 100 140 180 100 140 180 K- K+ K- K+ 2001 2003 years and fertilizing treatments

The actual evapotranspiration (ETa) defines the amount of water use (transpired and evapo‐

for a particular crop within a given geographical region, in spite of a slight year-to-year vari‐ ability. For example, indices of ETa calculated for maize in two contrastive growth seasons

CWP = Y /ET a a (8)

) by the cultivated crop during its growth period. Its value is constant

Legend: WLY – water limited yield; YG/YL – yield loss/gain, K-, K+ - K fertilizing

means with the same letter are not significantly different at α=0.05 (Tukey test).

**Figure 5.** Response of maize grown on soil differing in texture to increased fertilization level in 2006 (dry year); Source [55]

The water-management index describing water-use efficiency (WUE) refers to the quantity of biomass produced by a crop plant per volume of water transpired and evaporated during its life cycle. In agronomy, the WUE index termed as the crop water productivity (CWP) re‐ lates the quantity of actually harvestable or marketable crop plant part (seeds, grain, roots, tubers, etc.) produced on a given area in a fixed period of time (yield, Y) per unit of tran‐

2006 (dry year); Source [55]

0,000

2,000

a

a a

means with the same letter are not significantly different at α=0.05 (Tukey test).

**3.2. Impact of potassium on WUE – Maize as a case study**

4,000

6,000

yield of grain, t ha-1

150 Soil Fertility

8,000

10,000

12,000

a

a

from [62]



0

rated water) (mm, m3

2

4

6

yield of grain, t ha-1

8

spired water [59]:

10

12

14

16

treatments; 100, 140, 180 kg N ha-1.

a

2006 (dry year); Source [55]

0,000

2,000

a

a a

4,000

6,000

yield of grain, t ha-1

8,000

10,000

12,000

means with the same letter are not significantly different at α=0.05 (Tukey test).

NP. NPK NPKMg NPKMgNa NP. NPK NPKMg NPKMgNa loamy sand, L sandy loam, M soil textural class, fertilizing treatments

a

<sup>b</sup> <sup>b</sup>

c

a

from [62] Legend: WLY – water limited yield; YG/YL – yield loss/gain, K-, K+ - K fertilizing Legend: WLY – water limited yield; YG/YL – yield loss/gain, K-, K+ - K fertilizing treatments; 100, 140, 180 kg N ha-1.

Fig. 6. Effect of soil K fertility level on maize yield in two weather contrastive years; Adapted

**Figure 6.** Effect of soil K fertility level on maize yield in two weather contrastive years; Adapted from [62].
