**1. Introduction**

[17] Marschner H. Mineral nutritionof higher plants. New York: Academic Press; 1986.

[19] Monatanes L., Heras L., Sanz M. Desviación del optimo porcentual (DOP): nuevo ín‐ dice para la interpretación del análisis vegetal. Anales de Aula Dei 1991; 20 (3-4):

[20] Beaufils ER. Diagnosis and recommendation integrated system (DRIS): a general scheme of experimentation and calibration based on principles developed from re‐

[21] Walworth JL., Sumer RE. The diagnosis and recommendation integrated system

[22] Serra AP., Marchetti ME., Vitorino ACT., Novelino JO., Camacho MA. Determinação de faixas normais de nutrientes no algodoeiro pelos métodos CHM, CND e DRIS. Re‐

[23] Parent LE., Dafir M. A theoretical concept of compositional nutrient diagnosis. Jour‐

[24] Parent LE., Natale W. CND: Vantagens e benefícios para culturas de alta produtivi‐ dade. In: Prado RM., Rozane DE., Vale DW., Correia MAR., Souza HA. (Eds.). Nutri‐ ção de Plantas: Diagnose foliar em grandes culturas. Jaboticabal, Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista, FUNDENESP;

[25] Bollons HM., Barraclough PB. Assessing the phosphorus status of winter wheat crops: inorganic orthophosphate in whole shoots. Journal of Agricultural Science

[26] Bollons HM., Barraclough PB. Inorganic orthophosphate for diagnosing the phos‐ phorus status of wheat plants. Journal of Plant Nutrition 1997; 20 (6): 641-655.

nal of the American Society for Horticultura Science 1992; 117: 239-242.

search in plant nutrition. Pietermaritzburg: University of Natal; 1973. 132p.

(DRIS). Advances Soil Science 1987; 6: 149-188.

vista Brasileira de Ciência do Solo 2010; 34: 105-113.

[18] Malavolta, E. Manual de nutrição de plantas. Piracicaba: Ceres; 2006. 631p.

674p.

134 Soil Fertility

93-107.

2008. p.105-114.

1999; 133: 285-295.

Modern agriculture is under pressure of two contradictory challenges reflected by the increas‐ ing world's population on one hand, and the magnitude of food production, on the other hand. In the period ranging from 1960 to 2010, the population doubled from 3 to more than 6 billions, while the production of cereals tripled, a success which expressed by a significant yield in‐ crease per ha (from 1.09 t ha-1 in 1960 to 3.0 t ha-1 in 2010) [1]. The major reason of such yield in‐ crease was a marked progress in plant breeding, resulting in generations of new, high-yielding varieties [2]. This process run in parallel with the increase in fertilizers, pesticides production and consumption, hence enabling to cover nutritional needs and supporting the health of highyielding crops. The intensive production gain, based on enormous consumption of non-renew‐ able resources, especially fuel and simultaneously nutrients such as nitrogen and phosphorus was, however, concomitant with their low use efficiency. This type of agriculture intensifica‐ tion created, in many regions of the world a threat to environment, at both local and globalscale. There are numerous examples stressing the negative impact of intensive agriculture on environment. Agricultural practices are responsible for the majority of ammonia and to a great part for nitrogen oxide's emission to the atmosphere. Pollution of ground-water by nitrates and phosphates originating from both arable soils and surface waters was recognized the earliest. All these negative effects were the reason for the increased activity of local societies in the 70 and 80-ies of the XX century, resulting in the development of legal instruments protecting the environment, for instance the Nitrate Directive [3, 4, 5].

The complexity of agricultural impact on human life and the increasing awareness of envi‐ ronmental threats was the boosting argument for elaborating a concept of sustainable agri‐ culture growth [6]. The core of this concept relies on an assuming that agricultural systems

© 2012 Grzebisz et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Grzebisz et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

should be managed in a way covering current needs of present human being's population without negative impact on its performance in the future. The change of classical technolo‐ gies to fulfill both goals cannot be, however, achieved discrediting existing production methods. The analysis of two food supply scenarios, developed in the 90-ies, i.e., Yield Ori‐ ented Agriculture (YOA) and Environment Oriented Agriculture (EOA), implicitly shows that the second scenario guaranties the only moderate diet in 2040. By following this food production strategy, food shortage is expected in some regions of the world [7]. Therefore, the main challenges of modern agriculture are related to the improvement of classical pro‐ duction technologies. The future development scenarios cannot follow the concept of "sus‐ tainable intensification." This strategy, developed for low-input agriculture, assumes the substitution of external inputs by naturally available resources, both physical and human [8]. Therefore, the key challenge of agriculture is to increase resources use efficiency in all systems, independently on their current intensity. The general strategies of technological changes should include: i) improvement of water unit productivity, ii) increasing size of soil natural pools, i.e., resources affecting its fertility (organic carbon, macro- and micro-nu‐ trients), iii) reorientation of plant crop management of a single crop to the crop rotation iv) adopting no-till farming and conservation agriculture [2, 5, 9, 10, 11].

respective yield potential, which is as follows: 4.2, 3.4, 3.6, 4.6, 2.4 t ha-1, respectively. This virtually un-harvested portion of the potential yield has been termed as the yield gap.

Sustainable Management of Soil Potassium – A Crop Rotation Oriented Concept

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137

The third level of crop productivity depends on the supply of nutrients. However, produc‐ tion effects of applied nutrients are different, depending on a particular yield forming char‐ acteristic. Therefore, they can be classified to one of two main groups. The first one comprises only one nutrient, i.e., nitrogen. Its superiority over others is due to the decisive impact on primary plant physiological processes. The most important are those responsive for dry matter production, and its subsequent partitioning among organs during the whole life cycle of a plant [17]. Therefore, water and nitrogen are considered as the key limiting factors in the realization of the crop yield potential.. The effect of both factors on in-season crop performance depends on the supply of other nutrients. All of them are essential for the adequate plant growth, but are considered only as "secondary" in terms of their impact on yield performance and yielding potential exploration. Therefore, the Nutrient Limited Yield Gap (NLYG) can be related to the degree of both water- and nitrogen-use efficiency, i.e, WUE and NUE, respectively. The first one creates a milieu for nitrogen uptake and its fur‐ ther internal utilization. Thereby, the yield gap, due to inadequate uptake of nitrogen can be overcome provided the balanced supply of other nutrients. The question, remains how to

The main assumption of efficient nitrogen use is to apply nitrogen fertilizer in accordance to crop plant demands, which are variable during consecutive stages of growth. Farmers are aware of nitrogen and other nutrient's importance for increasing yield of growing crops as a prerequisite of high yield. However, they frequently make savings of their use, in turn decreas‐ ing nitrogen production efficiency. The key attribute of nitrogen-oriented crop production is its relatively low recovery from applied fertilizers, in turn negatively impacting the environment [4, 9]. In addition, the unbalanced nitrogen use leads to the depletion of natural resources of other nutrients required by crop plants. This situation, as shown in Fig. 1, is typical for coun‐ tries of the second and third group. In many Central-East European countries, yields of wheat decreased significantly in the 90-ies. The declining soil fertility is the main cause of the consid‐ erable year-to-year variability of harvested yields. The first step in reorientation of current agri‐ culture production into a sustainable way should, therefore, rely on the improvement of phosphorus and potassium management. The best example of this trend is China, which dou‐ bled during the last 20 years potassium consumption, resulting in a linear yield increase. The main goals of crop plants fertilization with potassium are to: i) reduce year-to-year variability

Potassium is one of the most important nutrients required by crop plants. In plants, its accumu‐ lation rate during early stages of growth precedes nitrogen accumulation. Therefore, its supply to plants seems to be decisive for nitrogen utilization, in turn significantly affecting plants growth rate and the degree of yield potential realization. The current status of potassium man‐ agement in world's agriculture, as presented in Table 1 and Fig. 1, has been evaluated on the ba‐ sis of potassium fertilizers consumption. Wheat has been considered as an example for assessing, the importance of this nutrient for food production. The consumption of potassium fertilizers in the period from 1986 to 2009 underwent significant changes on the world agricul‐

match a crop demand for nitrogen and other nutrients in time and space?

of harvested yields and ii) increase water- and N-use efficiency.

The efficient allocation of production means for improving yields and securing the environ‐ ment, requires a deep insight into processes responsible for crop's productivity. It is well recognized, that crop plant development during the growth season is controlled by numer‐ ous factors, both depended and independent on farmer's activity. All these factors have been arranged in a manner taking into account the degree of their impact on plant growth and productivity [12]. Four hierarchical levels of production factors and respective yield lev‐ els may be distinguished: i) potential, ii) water limited, iii) nutrient limited, iv) actual [13]. The first level of crop plant productivity is defined by climatic factors such as solar radia‐ tion, fixed by geographical location of the field. The potential productivity of the presently cultivated variety is defined by the capacity of its canopy to intercept solar radiation. This yield category is achievable, provided ample supply of water and nutrients during all stages of yield development [14]. For example, in Europe, the average yield potential of wheat was evaluated for the period 1996-2005 at the level of 10.4 t ha-1, however, ranged from 6.9 in Bulgaria to 12.7 t ha-1 in Ireland [15], depending on climatic factors.

Lal [10] has made an important remark concerning the exploitation of the yield potential of modern species. He pointed out that …"improved germplasm cannot extract water/ nutrients from degraded/depleted soils".... Water supply to plants during the vegetative sea‐ son is considered as the key limiting factor, defining the maximum achievable yield under physical conditions of the currently cropped field. In other words, this factor determines the site-specific, i.e., locally realizable yield. Any shortage of water supply throughout the growth season, especially during critical stages of yield formation is the primary reason of yield losses. In Europe, the water limited yield (WLY) is fixed at levels, showing declining trends in the directions extending from the West to the East and the South of the continent. For Ireland, it has been calculated at the level of 8.5, Germany and Poland – 6.5, Bulgaria, Romania – 4.5 t ha-1 [16]. However, WLYs show significant differences in comparison to the respective yield potential, which is as follows: 4.2, 3.4, 3.6, 4.6, 2.4 t ha-1, respectively. This virtually un-harvested portion of the potential yield has been termed as the yield gap.

should be managed in a way covering current needs of present human being's population without negative impact on its performance in the future. The change of classical technolo‐ gies to fulfill both goals cannot be, however, achieved discrediting existing production methods. The analysis of two food supply scenarios, developed in the 90-ies, i.e., Yield Ori‐ ented Agriculture (YOA) and Environment Oriented Agriculture (EOA), implicitly shows that the second scenario guaranties the only moderate diet in 2040. By following this food production strategy, food shortage is expected in some regions of the world [7]. Therefore, the main challenges of modern agriculture are related to the improvement of classical pro‐ duction technologies. The future development scenarios cannot follow the concept of "sus‐ tainable intensification." This strategy, developed for low-input agriculture, assumes the substitution of external inputs by naturally available resources, both physical and human [8]. Therefore, the key challenge of agriculture is to increase resources use efficiency in all systems, independently on their current intensity. The general strategies of technological changes should include: i) improvement of water unit productivity, ii) increasing size of soil natural pools, i.e., resources affecting its fertility (organic carbon, macro- and micro-nu‐ trients), iii) reorientation of plant crop management of a single crop to the crop rotation iv)

The efficient allocation of production means for improving yields and securing the environ‐ ment, requires a deep insight into processes responsible for crop's productivity. It is well recognized, that crop plant development during the growth season is controlled by numer‐ ous factors, both depended and independent on farmer's activity. All these factors have been arranged in a manner taking into account the degree of their impact on plant growth and productivity [12]. Four hierarchical levels of production factors and respective yield lev‐ els may be distinguished: i) potential, ii) water limited, iii) nutrient limited, iv) actual [13]. The first level of crop plant productivity is defined by climatic factors such as solar radia‐ tion, fixed by geographical location of the field. The potential productivity of the presently cultivated variety is defined by the capacity of its canopy to intercept solar radiation. This yield category is achievable, provided ample supply of water and nutrients during all stages of yield development [14]. For example, in Europe, the average yield potential of wheat was evaluated for the period 1996-2005 at the level of 10.4 t ha-1, however, ranged from 6.9 in

Lal [10] has made an important remark concerning the exploitation of the yield potential of modern species. He pointed out that …"improved germplasm cannot extract water/ nutrients from degraded/depleted soils".... Water supply to plants during the vegetative sea‐ son is considered as the key limiting factor, defining the maximum achievable yield under physical conditions of the currently cropped field. In other words, this factor determines the site-specific, i.e., locally realizable yield. Any shortage of water supply throughout the growth season, especially during critical stages of yield formation is the primary reason of yield losses. In Europe, the water limited yield (WLY) is fixed at levels, showing declining trends in the directions extending from the West to the East and the South of the continent. For Ireland, it has been calculated at the level of 8.5, Germany and Poland – 6.5, Bulgaria, Romania – 4.5 t ha-1 [16]. However, WLYs show significant differences in comparison to the

adopting no-till farming and conservation agriculture [2, 5, 9, 10, 11].

136 Soil Fertility

Bulgaria to 12.7 t ha-1 in Ireland [15], depending on climatic factors.

The third level of crop productivity depends on the supply of nutrients. However, produc‐ tion effects of applied nutrients are different, depending on a particular yield forming char‐ acteristic. Therefore, they can be classified to one of two main groups. The first one comprises only one nutrient, i.e., nitrogen. Its superiority over others is due to the decisive impact on primary plant physiological processes. The most important are those responsive for dry matter production, and its subsequent partitioning among organs during the whole life cycle of a plant [17]. Therefore, water and nitrogen are considered as the key limiting factors in the realization of the crop yield potential.. The effect of both factors on in-season crop performance depends on the supply of other nutrients. All of them are essential for the adequate plant growth, but are considered only as "secondary" in terms of their impact on yield performance and yielding potential exploration. Therefore, the Nutrient Limited Yield Gap (NLYG) can be related to the degree of both water- and nitrogen-use efficiency, i.e, WUE and NUE, respectively. The first one creates a milieu for nitrogen uptake and its fur‐ ther internal utilization. Thereby, the yield gap, due to inadequate uptake of nitrogen can be overcome provided the balanced supply of other nutrients. The question, remains how to match a crop demand for nitrogen and other nutrients in time and space?

The main assumption of efficient nitrogen use is to apply nitrogen fertilizer in accordance to crop plant demands, which are variable during consecutive stages of growth. Farmers are aware of nitrogen and other nutrient's importance for increasing yield of growing crops as a prerequisite of high yield. However, they frequently make savings of their use, in turn decreas‐ ing nitrogen production efficiency. The key attribute of nitrogen-oriented crop production is its relatively low recovery from applied fertilizers, in turn negatively impacting the environment [4, 9]. In addition, the unbalanced nitrogen use leads to the depletion of natural resources of other nutrients required by crop plants. This situation, as shown in Fig. 1, is typical for coun‐ tries of the second and third group. In many Central-East European countries, yields of wheat decreased significantly in the 90-ies. The declining soil fertility is the main cause of the consid‐ erable year-to-year variability of harvested yields. The first step in reorientation of current agri‐ culture production into a sustainable way should, therefore, rely on the improvement of phosphorus and potassium management. The best example of this trend is China, which dou‐ bled during the last 20 years potassium consumption, resulting in a linear yield increase. The main goals of crop plants fertilization with potassium are to: i) reduce year-to-year variability of harvested yields and ii) increase water- and N-use efficiency.

Potassium is one of the most important nutrients required by crop plants. In plants, its accumu‐ lation rate during early stages of growth precedes nitrogen accumulation. Therefore, its supply to plants seems to be decisive for nitrogen utilization, in turn significantly affecting plants growth rate and the degree of yield potential realization. The current status of potassium man‐ agement in world's agriculture, as presented in Table 1 and Fig. 1, has been evaluated on the ba‐ sis of potassium fertilizers consumption. Wheat has been considered as an example for assessing, the importance of this nutrient for food production. The consumption of potassium fertilizers in the period from 1986 to 2009 underwent significant changes on the world agricul‐ tural scene. The top wheat producers, mainly European countries and USA, showed a sharp de‐ clining trend in potassium usage in 2006-2009 as compared to 1986-1990. In 2005-2009, the group of main potassium consumers, compared to the period 1986-1990 decreased its use to 47%. Un‐ expectedly, in all these countries, any significant negative effect on wheat yields as induced by the decline in the consumption of potassium was noted. For example, grain yield increase aver‐ aged over all studied countries, amounted to 0.9 t ha-1, ranging from -0.3 for Denmark to +2.17 t ha-1 for Belgium (Table 1). Therefore, it can be concluded, that the recommended rates of potassi‐ um fertilizer did not fit real wheat requirements, both in time and space.

Potassium consumption pattern for Central and East European countries is much more com‐ plicated. It usage showed the same declining trend as in the previous group. However, in the second period, the average K consumption dropped down to 14.3% of its primary level. The mean change of wheat yield showed increase only for the Russian Federation and stag‐ nation for the Czech Republic. In other countries, a temporary yield gap (TYG), i.e., induced by the decrease in fertilizer's consumption ranged from -5% for Serbia to -23% for Bulgaria. The relative change (ΔY) of wheat yield as presented below, followed the degree of potassi‐ um consumption change (ΔK):

$$
\Delta \mathbf{Y} = 1.47 \Delta \mathbf{K} + 114.2; \mathbf{R}^2 = 0.66, \mathbf{n} = 7 \text{ and } \mathbf{P} \le 0.01 \tag{1}
$$

These three examples, presenting potassium management by main wheat producers, implic‐ itly indicate that there is a significant gap between official K recommend rates and real needs of wheat for fertilizer potassium. It is necessary to agree with opinions expressed fre‐ quently by farmers, about the inappropriateness of current nutrient recommendations and especially regarding the transfer of scientific knowledge to agriculture practice. Consequent‐ ly, each method of N management requires, firstly, a simple and secondly, a reliable method of other nutrient's recommendations in terms of the amount and of time, as the guarantee of

Sustainable Management of Soil Potassium – A Crop Rotation Oriented Concept

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139

This conceptual review assumes that sustainable potassium management on the field should focus farmer's activity on increasing both: i) the amount of available K pool and ii) access of crops grown in a given cropping sequence to this resources. The primary objective of this paper is to present and explain the scientific background of potassium impact on crop plant's growth and productivity, taking into account their different sensitivity to K supply, both in the required quantity and time. The key objective is to stress the importance of the crop rotation-oriented strategy of potassium management, considered as the low input method. It focusses on covering K requirements of the most sensitive crop during its critical stages of yield formation. It is also supposed, that K soil sufficiency can be partly achieved

Fig.1. Effect of relative change of potassium fertilizer consumption on relative wheat yield change (1986-1990 = 100%); source: FAOSTAT, IFADATA, available online 2012-08-07

**Figure 1.** Effect of relative change of potassium fertilizer consumption on relative wheat yield change (1986-1990 =

relative change of K consumption, (x) %


Y = 0.01x + 13.76

= 0.39 for n = 24 and P < 0.001

P

N K

nutrient

R2

Fig. 2. General pattern of K and N accumulation in high-yielding crops, a case of sugar beet;

29-05 18-06 8-07 28-07 17-08 6-09 26-09 16-10 5-11 calendar dates

5

by recycling of organic K sources, taking into account the crop rotation course.

available N efficient use.

GrzebiszFigures

HP

I

relative change of wheat grain yield, (Y) %

100%).

Legend: HP, I, P – groups of countries.

0

20

40

60

80

realative N and K accumualtion %

100

120

140

Legend: HP, I, P – groups of countries




0

10

20

30

40

50

60

Source [21]

The third group consists of low potassium fertilizer consumers (based on data for the 1986-1990 period). Most of them showed an extremely huge K consumption increase in the period extending from 1990 to 2009. This high progress resulted in the net yield of wheat gain, as presented below:

$$
\Delta \mathbf{Y} = 0.13 \Delta \mathbf{K} + 4.83; \mathbf{R}^2 = 0.61, \mathbf{n} = 7 \text{ and } \mathbf{P} \le 0.01 \tag{2}
$$


1source: FAOSTAT, IFADATA, available online 2012-08-07;

2group HP (high productive countries): Austria, Belgium, Denmark, France, Germany, Italy, The Netherlands, Spain, United Kingdom, United States of America;

3group I (intermediate): Bulgaria, Czech Republic, Hungary, Romania, Russian Federation, Serbia, Slovak Republic, Ukraine;

4group P (progressive): Argentina, Australia, China, Egypt, India, Mexico, Turkey.

**Table 1.** Statistical overview of potassium consumption by wheat producers in two distinct periods1, kg K2O ha-1

These three examples, presenting potassium management by main wheat producers, implic‐ itly indicate that there is a significant gap between official K recommend rates and real needs of wheat for fertilizer potassium. It is necessary to agree with opinions expressed fre‐ quently by farmers, about the inappropriateness of current nutrient recommendations and especially regarding the transfer of scientific knowledge to agriculture practice. Consequent‐ ly, each method of N management requires, firstly, a simple and secondly, a reliable method of other nutrient's recommendations in terms of the amount and of time, as the guarantee of available N efficient use.

This conceptual review assumes that sustainable potassium management on the field should focus farmer's activity on increasing both: i) the amount of available K pool and ii) access of crops grown in a given cropping sequence to this resources. The primary objective of this paper is to present and explain the scientific background of potassium impact on crop plant's growth and productivity, taking into account their different sensitivity to K supply, both in the required quantity and time. The key objective is to stress the importance of the crop rotation-oriented strategy of potassium management, considered as the low input method. It focusses on covering K requirements of the most sensitive crop during its critical stages of yield formation. It is also supposed, that K soil sufficiency can be partly achieved by recycling of organic K sources, taking into account the crop rotation course.

relative change of K consumption, (x) %

change (1986-1990 = 100%); source: FAOSTAT, IFADATA, available online 2012-08-07 Legend: HP, I, P – groups of countries

Source [21]

Legend: HP, I, P – groups of countries.

0

20

40

60

80

realative N and K accumualtion %

100

120

GrzebiszFigures

tural scene. The top wheat producers, mainly European countries and USA, showed a sharp de‐ clining trend in potassium usage in 2006-2009 as compared to 1986-1990. In 2005-2009, the group of main potassium consumers, compared to the period 1986-1990 decreased its use to 47%. Un‐ expectedly, in all these countries, any significant negative effect on wheat yields as induced by the decline in the consumption of potassium was noted. For example, grain yield increase aver‐ aged over all studied countries, amounted to 0.9 t ha-1, ranging from -0.3 for Denmark to +2.17 t ha-1 for Belgium (Table 1). Therefore, it can be concluded, that the recommended rates of potassi‐

Potassium consumption pattern for Central and East European countries is much more com‐ plicated. It usage showed the same declining trend as in the previous group. However, in the second period, the average K consumption dropped down to 14.3% of its primary level. The mean change of wheat yield showed increase only for the Russian Federation and stag‐ nation for the Czech Republic. In other countries, a temporary yield gap (TYG), i.e., induced by the decrease in fertilizer's consumption ranged from -5% for Serbia to -23% for Bulgaria. The relative change (ΔY) of wheat yield as presented below, followed the degree of potassi‐

The third group consists of low potassium fertilizer consumers (based on data for the 1986-1990 period). Most of them showed an extremely huge K consumption increase in the period extending from 1990 to 2009. This high progress resulted in the net yield of wheat

**HP2 I**

Average 51.4 23.6 53.9 7.75 4.85 14.5

2group HP (high productive countries): Austria, Belgium, Denmark, France, Germany, Italy, The Netherlands, Spain,

3group I (intermediate): Bulgaria, Czech Republic, Hungary, Romania, Russian Federation, Serbia, Slovak Republic, Ukraine;

**Table 1.** Statistical overview of potassium consumption by wheat producers in two distinct periods1, kg K2O ha-1

<sup>2</sup> ΔY = 1.47ΔK + 114.2; R = 0.66, n = 7 and P 0.01 £ (1)

<sup>2</sup> ΔY = 0.13ΔK + 4.83; R = 0.61, n = 7 and P 0.01 £ (2)

**1986-90 2005-2009 1986-90 2005-2009 1986-90 2005-2009**

30.2 14.7 24.7 4.46 4.46 15.4

58.8 62.3 45.8 57.5 91.9 106.1

**<sup>3</sup> P4**

um fertilizer did not fit real wheat requirements, both in time and space.

um consumption change (ΔK):

gain, as presented below:

1source: FAOSTAT, IFADATA, available online 2012-08-07;

4group P (progressive): Argentina, Australia, China, Egypt, India, Mexico, Turkey.

United Kingdom, United States of America;

**Statistical characteristics**

138 Soil Fertility

Standard deviation

Coefficient of variation, %

> 140 **Figure 1.** Effect of relative change of potassium fertilizer consumption on relative wheat yield change (1986-1990 = 100%).

Fig. 2. General pattern of K and N accumulation in high-yielding crops, a case of sugar beet;

29-05 18-06 8-07 28-07 17-08 6-09 26-09 16-10 5-11 calendar dates

Fig.1. Effect of relative change of potassium fertilizer consumption on relative wheat yield

5

N K

nutrient
