IMPHOS AGRONOMIC PROGRAMS IN ASIA
The importance of phosphate fertilizer for increased crop production in developing countries THE IMPORTANCE OF PHOSPHATE FERTILIZER FOR INCREASED CROP PRODUCTION IN DEVELOPING COUNTRIES AFA 6th International Annual Conference 31 January – 2 February 2000, Cairo, Egypt L. Cisse & B. Amar The World Phosphate Institute, Casablanca, Morocco INTRODUCTION The twin challenges of food security and environmental protection in the developing countries require that these countries increasingly rely on science-based agriculture. With regard to that increased use of mineral fertilizer, including management of environmental problems without loosing the productivity benefits of fertilizers, will play a critical role. The role of mineral fertilizer for increased food production, in particular in developing countries, is well established. Over the past 30 years, there has been a positive correlation between cereal production and fertilizer use in these countries (Daberkow, et al, 1999). This relationship is illustrated in Figure 1. Figure 1 : Fertilizer consumption and cereal production in developping countries, Million tons
(Source : FAO)
The annual growth in fertilizer use in developing countries was 10.5 and 2.2 % during the periods 1960-1990 and 1990-2000, respectively (Bumb and Baanante, 1996).
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The importance of phosphate fertilizer for increased crop production in developing countries The application of essential plant nutrients, particularly major and micronutrients in optimum quantity and right proportion, through correct method and time of application, is the key to increased and sustained crop production. If any plant nutrient is deficient, crop growth will be affected. But one of the major constraints to increased crop production in most parts of the world has always been the small or very small amounts of naturally occurring, plant available phosphorus in soil. Deficiency of phosphorus is widespread in Asia, Latin America, North Africa, and Sub-Saharan Africa. In relation to plant growth, sufficient P nutrition improves several plant processes that include photosynthesis, nitrogen fixation, flowering, fruiting, seed formation, root development, and crop maturation. This paper presents data and information on the essential role of P in crop production largely drawing on work conducted by the fertilizer industry, international organizations and agricultural research centers in North Africa and West Asia (WANA) and Asia. In particular, it will emphasis the role of P fertilizer in promoting food production in the food-deficiency countries in these regions, factors affecting P fertilizer efficiency, and prospects for improving its agronomic efficiency. EFFECTS OF PHOSPHORUS FERTILIZER ON CROP YIELDS In the WANA region, P205 consumption totaled 1.7 million tons in 1996 (FAO, Yearbook 1997). The average use on annual crop is around 19 kg/ha P2O5. This amount is less than the average recommendation for cereals, which ranges from 30 kg/ha, on soil having between 6 to 10 ppm of Olsen-P to 60 kg/ha, on soils with less than 5 ppm Olsen-P (Matar, 1987). In studies conducted in several countries within the region, including Algeria, Cyprus, Iran, Jordan, Morocco, Syria, Tunisia, and Turkey, significant yield increases were obtained following P applications on barley, wheat, and chickpea. Yield increases over control varying from 9 to 65 % were recorded on barley in Syria, with 60 kg/ha of P2O5. In Jordan, on wheat the application of 40 and 80 kg/ha of P2O5 resulted in 5 and 23 % increase, respectively. In South-East Asia, where tremendous cereal production increases were recorded over the past 30 years, amounting in 1996 to 897.9 million tons, and representing 43.8 % of the world cereal production (FAO, Yearbook 1997), P2O5 consumption increases steadily amounting to 7.3, 12.2, and 14,2 million tons in 1985, 1990, and 1997, respectively.
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The importance of phosphate fertilizer for increased crop production in developing countries On cereals responses to P applications, expressed as amount of additional crop produced per kg of P2O5 applied (i. e Productivity Index), obtained in some countries are presented in Table 1. Table 1 : Cereal responses to applied phosphorus in some countries Crop/Country
No. of observations
P2O5 (kg/ha)
Productivity Index
Wheat Pakistan, irrigated Pakistan, rainfed India, irrigated China Bangladesh
1821 1024 3768 1851 1042
100 60 60 81 67
6.1 6.4 8.2 8.1 6.0
Rice Pakistan, irrigated India, irrigated China Sri Lanka Thailand Indonesia Philippines
480 2969 921 534 405 688 887
90 60 58 80 52 45 30
Maize Pakistan, irrigated India, irrigated China Indonesia
1420 354 10401 312
90 60 84 45
11.1 09.5 04.7 08.6 06.3 06.9 08.5 07.9 10.3 09.7 08.8
Source: derived from FAO: Fertilizer and Food Production, 1989 Productivity Index: Kg of additional grain produced per kg of P2O5 applied
The productivity index varies between 5 and 11; extremes are rice in China (4.7) and rice irrigated rice in Pakistan (11.1) with P2O5 application of 58 and 90 kg per hectare, respectively. For the same crops, the productivity index for N was in the range of 8-12. Data on oil crops and cotton responses to applied P fertilizers are presented in Table 2. The highest productivity index is 6.0 (on groundnut and mustard) and the lowest is 2 (on soybean). The corresponding values for N are 12 and 2 obtained on groundnut and mustard, respectively. In the Indo-Gangetic Plains (IGP), on rice-wheat systems, notable yield responses were obtained, in particular on wheat, following application of 60 kg/ha of P2O5 (Table 3-a). In these regions rice generally responded up to 30 kg/ha P2O5 while wheat responded up to twice even three times this amount (Table 3-b). Survey conducted in the areas intensively cropped with rice-wheat in the IGP indicates that 46 % of the soils have low soil P status, 50 % and 4 % have medium and high P status, respectively. P fertilizers are an important input for maintaining and enhancing the productivity of the intensive rice-wheat cropping systems (Abrol, 1996).
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The importance of phosphate fertilizer for increased crop production in developing countries Table 2 : Responses of oil crops and cotton to applied phosphorus in some countries Crop/Country
No. of observations
P2O5 (kg/ha)
Productivity Index
2619 112 370
40 60 45
6.0 4.6 3.2
213
45
2.1
1117 94
40 67
6.0 3.5
1866 71
50 38
4.6 4.8
Groundnut India Sri Lanka Indonesia Soybean Pakistan Mustard India Bangladesh Cotton Pakistan Thailand
Source: derived from FAO: Fertilizers and Food Production, 1989 Productivity Index: Kg of additional crop produced per Kg of P2O5 applied
Table 3-a : Wheat response to applied phosphorus in a rice-wheat cropping system in the in the Indo-Gangetic Plains in Asia P2O5 applied (kg/ha) Rice
Wheat
60 0 60
Wheat grain yield (t/ha)
0 60 60
2.7 4.3 4.4
Source: Abrol, 1998
Table 3-b : Wheat response to increasing doses of phosphorus P2O5 (kg/ha)
Wheat grain yield (t/ha)
0 60 90 120
2.3 3.8 4.6 4.7
Source: Syers, 1998
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The importance of phosphate fertilizer for increased crop production in developing countries The agricultural productivity of the vast area of approximately 100 million hectares of upland acid soils, originally covered by natural forests, is severely limited by P deficiency and soil acidity. On these acid upland soils soluble P fertilizers and reactive phosphate rocks increase crop yields several fold. Results obtained on rice and soybean in Indonesia, and on rice, maize, and groundnut in Vietnam with the use of soluble P and reactive phosphate rock are presented in Tables 4-a and 4-b. Table 4-a : Rice and soybean responses to water soluble P fertilizer and reactive phosphate Rock (in Indonesia) Treatments
Paddy rice (t/ha)
Soybean (t/ha)
Control TSP RPR
1.4 3.6 3.2
0.03 0.33 0.30
Source: Adiningsih, 1998
- RPR : reactive phosphate rock
Table 4-b : Rice, maize, and groundnut responses to water soluble P fertilizer and reactive phosphate rock (in Vietnam) Treatments
Paddy rice (t/ha)
Maize (t/ha)
Groundnut (t/ha)
Control SSP RPR
3.3 4.0 4.1
0.6 2.3 1.6
1.3 2.0 1.7
Source: Binh, 1998
- RPR: reactive phosphate rock
While the demand for rice in relative terms is currently diminishing in Asia, that for coarse grains, pulses, animal products and vegetables is increasing. These crops and products are best grown on the upland in this region. The above results emphasize the importance of applying phosphate fertilizers to first increase and then sustain soil fertility and hence the ability to grow good crops with rice yield above 4 t /ha, groundnut yield around 2 t/ha, and 6 t/ha of maize grain (Uexkull, 1996). Phosphorus deficiency is widespread in the WANA region and Asia given that inherently low P status is characteristic of large areas of soils. Unless P limitations to production are addressed in these regions, resource-poor farmers will continue to face low food crop production and income. In particular, in Asia, which is increasingly depending on imports of commodities such as wheat, maize, animal products, and increased phosphorus fertilization of upland soils is needed to achieve sustained and increased food production.
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The importance of phosphate fertilizer for increased crop production in developing countries FACTORS AFFECTING P FERTILIZERS EFFICIENCY The agronomic efficiency, which can be measured as yield increase per unit fertilizer input, covers at least three aspects that are application efficiency, uptake efficiency, and utilization efficiency (Krishna, 1997). Nutrient use efficiency, in particular P use efficiency, depends on the boundaries where inputs and outputs are measured: crop level, farm level and various components of the farm, landscape area, country level, etc… Unlike N, fertilizer P must be obtained by extractive mining industries and therefore its supply is finite. It should be used efficiently in agriculture to maintain P supplies to crops and minimize its loss to the environment. Among factors affecting P fertilizer efficiency are genetic variation within crop species, even between cultivars within a crop specie, form and type of fertilizer, soil characteristics and their interactions with crop grown on, and the production environment that includes technological, agroecological, and economic factors. Crop species Crops differ in their ability to take up P from the soil solution. These differences include root morphology, in particular, root length and diameter, physiological characteristics, and rhizosphere environment. These traits and characteristics are gene-governed, and the components of genetic variation for P efficiency in crops include: (1)-acquisition of P from soil, which relates to efficient root system, physiological efficiency of P uptake per unit of root length, longevity of roots, ability of roots to modify rhizosphere and enhance P availability to roots via exudation of biochemical substances; (2)-movement of P across roots and delivery to the xylem; (3)-distribution of P within plant; (4)-metabolic activity; (5)- and polyploidy and hybrid levels. Some species of crops such as lupins, canola have the capacity to significantly modify the environment of their root system, particularly under stress condition, which can increase their absorption of P several fold. They have a great production of some enzymes (citrate synthase and malate dehydrogenase) that increase the availability of soil P (Johnson et al, 1994). Development of new varieties that include traits that increase P use efficiency could impact P fertilizer application and consumption. Research is underway in most of developed countries to increase P uptake and efficiency in crops such as wheat, maize, beans, tomato, and white clover. It is focussed on utilizing genes for mechanisms to increase P uptake and efficiency. The genetic manipulation aims at altering the P concentration at the root surface and therefore the optimum soil P level for the crop. Plants can be therefore engineered to improve their P use efficiency but also their nutritional content, which can lead in many developing countries to not only increased food availability, but also to better health (Mahendra et al, 1999). Farming in major cropping zones of Asia, West Asia and North Africa is conducted under low fertility condition with soil-P deficiency as a severe production constraint. Such development can help provide optimum production levels of various crops.
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The importance of phosphate fertilizer for increased crop production in developing countries Balanced fertilizer Use The need for increased production to meet expanding food, fiber and fuel requirements of a continuously growing population is recognized worldwide. It also recognized that sustainability might include this need while addressing food adequacy in the future and the protection of the environment. Further, sustainable agriculture requires efficient management of resources, in particular, of fertilizer inputs. Increasing nutrient balances (the N: P2O5: K2O ratio) can enhance nutrient use efficiency. In many developing countries N use, in relation to P2O5 and K2O use, is excessive (Bumb et al, 1996). This reduces the efficiency of all nutrients, in particular N, and results from the tendency in many developing countries to save foreign exchange by minimizing imports of P2O5 and K2O fertilizer. But this does many harms because it reduces returns on investment in N fertilizer, leads to degradation of soils and causes environmental problems. For appropriate plant nutrition, it is essential to provide the required amount of each nutrient and establish the correct balance between the plant nutrients. Different crops need or remove nutrients from the soil in different ratios. Legumes need nutrients in ratio of 0:1:1 or1: 2:2 or 1:2:3, root crops, 2:1:2, and other crops, a ratio of 2:1:1 or 1:1:1 (PPIC, 1998). Table 5 shows the N: P2O5 ratios in 12 countries in the WANA. For many countries, these ratios indicate an imbalance in the use of P and K. In addition P2O5 applications are low, around 19 kg/ha on wheat, compared with offtake that averages 29 kg/ha P2O5 by wheat yielding 2.8 t/ha. The imbalance in P and K and low level of application of these nutrients limit crop yields, in particular under rainfed conditions, as reported in several publications from the region (Johnston, 1997). Table 5 : Ratio of N : P2O5 in 12 WANA region countries Countries Algeria Egypt Iran Iraq Israel Jordan Libya Morocco Saudi Arabia Syria Tunisia Turkey
N
P2O5
1 1 1 1 1 1 1 1 1 1 1 1
0.64 0.14 0.60 0.59 0.44 2.00 1.83 0.78 0.79 0.59 0.83 0.44
Source: Johnston, 1997
In many countries within Asia, fertilizer use is unbalanced in favor of nitrogen. This stems from the relative low cost per unit of nutrient of nitrogen fertilizers and their widespread availability. In Table 6 are presented recent N: P2O5 ratios in China, India, and Pakistan. These data show that N applications are 3 to 4 times higher than P applications. On rice this unbalance nutrient use results in lodging, greater weed competition and pest attacks, with paddy yield losses of about 20 %, but can reach 50 % under some conditions (FAO, 1995).
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The importance of phosphate fertilizer for increased crop production in developing countries Results obtained in India (Table 7) and Pakistan (Table 8) clearly show the yield and farmer’s income losses resulting to nil or low phosphorus fertilizer application compared to nitrogen. Table 6 : Ratio of N : P2O5 in China, India, and Pakistan Years
China
India
Pakistan
1991 1993 1995 1997
1 : 0.40 1 : 0.43 1 : 0.47 n.a
1 : 0.41 1 : 0.31 1 : 0.38 1 : 0.29
1 : 0.26 1 : 0.28 1 : 0.25 1 : 0.23
Sources: Xie, 1998; PPIC, 1998; and others
Table 7 : Effect of balanced N and P fertilization on the yield of some crops in Asia Crops
Rice Rice Rice Wheat Sorghum Pearl millet Chickpea Pigeonpea Cotton
Season & conditions
No. of observations
Mean yield(t/ha) without fertilizer
Unirrigated Irrigated/spring Irrigated /winter Irrigated Unirrigated „ „ „ „
380 9634 5686 10133 389 207 1325 53 55
2.4 3.0 3.2 1.6 0.6 0.5 0.8 0.3 0.3
% yield increase / unfertilization N 49 27 28 59 56 54 36 97 44
NP 74(51) 51(89) 51(82) 95(61) 92(64) 110(104) 59(64) 210(116) 91(107)
P applications (kg/ha P2O5) = 60, except on chickpea (40) N applications (kg/ha N) = 120 on rice and wheat; 90 on other cereals; and 20 on chickpea and pigeonpea (): additional increase resulting from P application
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The importance of phosphate fertilizer for increased crop production in developing countries Table 8 : Economic response to P fertilizer applications on some crops Province
N-P2O5 application 75-0 75-60
Year
Crop
Value cost ratio
Punjab
1997/1998
Rainfed wheat
Punjab
1997/1998
Irrigated wheat
120-0 120-90
3.7 (N) 3.2 (P)
Punjab
1998
Irrigated cotton
150-0 150-60
3.7 (N) 6.3 (P)
Punjab
1998
Irrigated maize
120-0 120-90
5.8 (N) 9.3 (P)
Punjab
1998
Irrigated rice
120-0 120-60
4.7 (N) 5.9 (P)
Balochistan
1998
Onions
150-0 150-100
9.8 (N) 13.3 (P)
N.. W. Frontier
1997
Sugarcane
150-0 150-75
3.3 (N) 12.0 (P)
3.2 (N) 3.5 (P)
Source: IMPHOS/FAO/NFDC project in Pakistan, 1999 N.W: North West
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The importance of phosphate fertilizer for increased crop production in developing countries P fertilization practices Phosphate fertilizer application methods can affect the efficiency of the applied phosphorus. Over several years, many application methods were tested under different cropping systems. These methods include broadcasting, banding, point placement, split applications. In Egypt and Pakistan, trials conducted on rice showed that P fertilizers are used most effectively when placed 5 cm below the soil surface (IAEA/FAO Joint Division, 1995). On maize, mixed application of N and P fertilizers at seeding increased the uptake of both P and N by 1520 %. Banding application of P resulted in higher maize yield (45 %) than broadcasting. In India, for upland crops results are overwhelming in favor of drilling and placing P below the soil surface and into the root zone (Abrol, 1998). Under irrigated conditions wheat yield increases of 400-700 kg/ha are common when P is placed or drilled compared with surface broadcasting (Tandon, 1987). In Asia, much research has defined both application methods and timing for increasing the efficiency of P. In study on fodder crop conducted in Pakistan (Alam, 1998), application of 50 kg/ha P2O5 by fertigation resulted in equivalent fodder yield as obtained by broadcasting application of 100 kg/ha P2O5. The agronomic efficiency and P fertilizer efficiency were all higher where P was applied by fertigation compared with broadcast application. Irrespective of the sources tested (Triple superphosphate, Diammonium phosphate, Urea phosphate), P applied with the irrigation water was more effective than direct soil application on tomato, sweet pepper and eggplant, in field trials conducted in Cyprus (Ristimaki et al, 1999). Yields of tomatoes increased by as much as 35 % when fertigation was employed. In line with several other studies, these results indicated that P application by fertigation is a far more efficient method than conventional soil P application. Crop management, in particular crop rotation, affected also P use efficiency. Results from China (Xie et al, 1996) showed that applying P fertilizers on the dry season crop in a rice-dry season crop rotation improved the efficiency in the forest season and increased the availability of residual P for rice. The application of P fertilizer together with organic manure results in general to increased agronomic P efficiency on rice cultivation. On heavy textured and high P fixation capacity soils, organic matter reduces soil fixation of applied P, while under other conditions it stimulates root growth, and on overall increases P uptake by crops. Application of organic matter at 4.8 t/ha, in combination with liming, on an Ultisol in West Java, improved the applied P fertilizer and increased the yield of maize from 33.5 to 56 kg grain per kg of P applied (Santoso, 1998). The appropriate assessment of crop P requirement using conventional soil testing methods or other method such as COMIFER (French Committee for Development of Rational Fertilization) approach is also of paramount importance to increasing P use efficiency. Example from IFFCO (Indian Farmers Fertiliser Cooperative) work conducted from 1992 to 1995 on 15 crops in 108 villages covering 92 districts in 14 states in India (Kumar, 1998) showed clearly the benefit associated with using soil test-based P (and other nutrients) recommendations, which increase yield and cost-benefit ratios.
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The importance of phosphate fertilizer for increased crop production in developing countries Diagnostic technique and Phosphate fertilization strategies Data from several laboratory and field experiments suggest that phosphorus is one of the most limiting nutrients to crop production in soils of the Mediterranean region. Therefore, it would be helpful to develop techniques that would enable farmers of the region to make proper use of P fertilizer to meet the demand of the plant-soil system, thereby increasing productivity and economic return. To that effect, the World Phosphate Institute (IMPHOS) in collaboration with National Agricultural Research Centers of 9 countries of the Mediterranean region set out to conduct a survey of phosphorus fertilization practices at farm level and to undertake under greenhouse a series of pot trials. The countries involved in the survey are Algeria, Egypt, France, Jordan, Morocco, Spain, Syria, Tunisia, and Turkey. Through the survey and greenhouse pot trials a mass of data was collected. With the collaboration of “Europe Sols”, a laboratory of plant and soil analyses in Toulouse-France, data processing obeyed the principles set out by the French Committee for Development of Rational Fertilization (COMIFER). COMIFER approach proceeds in two stages as illustrated in Figure 2. Figure 2 : COMIFER approach for diagnostic and prescription of phosphate fertilization recommendation
The stage of diagnosis: In order to assess soil P availability for the whole Mediterranean region, 4 parameters were considered based on the COMIFER approach: • Crop P requirement: crops were divided into three classes according to their P requirement: low, medium, and high (Table 9). • Field fertilization history: It was determined based on both the P balance at field level (P application minus crop removal) and the soil phosphorus fixing capacity. Accordingly, fields were classified as having favorable, medium or unfavorable P fertilization history (Table 10). • Crop residue management: The assumption is that all crop residues are removed from field and no P is restituted to the soil from such residues. • Soil P content: Greenhouse pot trials were used to assess plant responses to P fertilizer application over a wide range of soils of various characteristics. Two values of soil P content !
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The importance of phosphate fertilizer for increased crop production in developing countries were important to determine. The critical value (Tc) below which it is recommended to increase P application rate over the maintenance rate in order to build up soil P fertility, and the sufficient (breakeven) value (Ts) above which it is recommended not to apply any P fertilizer over a period of time. For the Tc value, Soil Olsen-P ranged from 10 to15 ppm P2O5 whereas it ranged from 50 to 55 ppm P2 O5 for the Ts value (Figure3). Figure 3 : Distribution of crop response to P application (IC
(Source : FAO)
The annual growth in fertilizer use in developing countries was 10.5 and 2.2 % during the periods 1960-1990 and 1990-2000, respectively (Bumb and Baanante, 1996).
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The importance of phosphate fertilizer for increased crop production in developing countries The application of essential plant nutrients, particularly major and micronutrients in optimum quantity and right proportion, through correct method and time of application, is the key to increased and sustained crop production. If any plant nutrient is deficient, crop growth will be affected. But one of the major constraints to increased crop production in most parts of the world has always been the small or very small amounts of naturally occurring, plant available phosphorus in soil. Deficiency of phosphorus is widespread in Asia, Latin America, North Africa, and Sub-Saharan Africa. In relation to plant growth, sufficient P nutrition improves several plant processes that include photosynthesis, nitrogen fixation, flowering, fruiting, seed formation, root development, and crop maturation. This paper presents data and information on the essential role of P in crop production largely drawing on work conducted by the fertilizer industry, international organizations and agricultural research centers in North Africa and West Asia (WANA) and Asia. In particular, it will emphasis the role of P fertilizer in promoting food production in the food-deficiency countries in these regions, factors affecting P fertilizer efficiency, and prospects for improving its agronomic efficiency. EFFECTS OF PHOSPHORUS FERTILIZER ON CROP YIELDS In the WANA region, P205 consumption totaled 1.7 million tons in 1996 (FAO, Yearbook 1997). The average use on annual crop is around 19 kg/ha P2O5. This amount is less than the average recommendation for cereals, which ranges from 30 kg/ha, on soil having between 6 to 10 ppm of Olsen-P to 60 kg/ha, on soils with less than 5 ppm Olsen-P (Matar, 1987). In studies conducted in several countries within the region, including Algeria, Cyprus, Iran, Jordan, Morocco, Syria, Tunisia, and Turkey, significant yield increases were obtained following P applications on barley, wheat, and chickpea. Yield increases over control varying from 9 to 65 % were recorded on barley in Syria, with 60 kg/ha of P2O5. In Jordan, on wheat the application of 40 and 80 kg/ha of P2O5 resulted in 5 and 23 % increase, respectively. In South-East Asia, where tremendous cereal production increases were recorded over the past 30 years, amounting in 1996 to 897.9 million tons, and representing 43.8 % of the world cereal production (FAO, Yearbook 1997), P2O5 consumption increases steadily amounting to 7.3, 12.2, and 14,2 million tons in 1985, 1990, and 1997, respectively.
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The importance of phosphate fertilizer for increased crop production in developing countries On cereals responses to P applications, expressed as amount of additional crop produced per kg of P2O5 applied (i. e Productivity Index), obtained in some countries are presented in Table 1. Table 1 : Cereal responses to applied phosphorus in some countries Crop/Country
No. of observations
P2O5 (kg/ha)
Productivity Index
Wheat Pakistan, irrigated Pakistan, rainfed India, irrigated China Bangladesh
1821 1024 3768 1851 1042
100 60 60 81 67
6.1 6.4 8.2 8.1 6.0
Rice Pakistan, irrigated India, irrigated China Sri Lanka Thailand Indonesia Philippines
480 2969 921 534 405 688 887
90 60 58 80 52 45 30
Maize Pakistan, irrigated India, irrigated China Indonesia
1420 354 10401 312
90 60 84 45
11.1 09.5 04.7 08.6 06.3 06.9 08.5 07.9 10.3 09.7 08.8
Source: derived from FAO: Fertilizer and Food Production, 1989 Productivity Index: Kg of additional grain produced per kg of P2O5 applied
The productivity index varies between 5 and 11; extremes are rice in China (4.7) and rice irrigated rice in Pakistan (11.1) with P2O5 application of 58 and 90 kg per hectare, respectively. For the same crops, the productivity index for N was in the range of 8-12. Data on oil crops and cotton responses to applied P fertilizers are presented in Table 2. The highest productivity index is 6.0 (on groundnut and mustard) and the lowest is 2 (on soybean). The corresponding values for N are 12 and 2 obtained on groundnut and mustard, respectively. In the Indo-Gangetic Plains (IGP), on rice-wheat systems, notable yield responses were obtained, in particular on wheat, following application of 60 kg/ha of P2O5 (Table 3-a). In these regions rice generally responded up to 30 kg/ha P2O5 while wheat responded up to twice even three times this amount (Table 3-b). Survey conducted in the areas intensively cropped with rice-wheat in the IGP indicates that 46 % of the soils have low soil P status, 50 % and 4 % have medium and high P status, respectively. P fertilizers are an important input for maintaining and enhancing the productivity of the intensive rice-wheat cropping systems (Abrol, 1996).
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The importance of phosphate fertilizer for increased crop production in developing countries Table 2 : Responses of oil crops and cotton to applied phosphorus in some countries Crop/Country
No. of observations
P2O5 (kg/ha)
Productivity Index
2619 112 370
40 60 45
6.0 4.6 3.2
213
45
2.1
1117 94
40 67
6.0 3.5
1866 71
50 38
4.6 4.8
Groundnut India Sri Lanka Indonesia Soybean Pakistan Mustard India Bangladesh Cotton Pakistan Thailand
Source: derived from FAO: Fertilizers and Food Production, 1989 Productivity Index: Kg of additional crop produced per Kg of P2O5 applied
Table 3-a : Wheat response to applied phosphorus in a rice-wheat cropping system in the in the Indo-Gangetic Plains in Asia P2O5 applied (kg/ha) Rice
Wheat
60 0 60
Wheat grain yield (t/ha)
0 60 60
2.7 4.3 4.4
Source: Abrol, 1998
Table 3-b : Wheat response to increasing doses of phosphorus P2O5 (kg/ha)
Wheat grain yield (t/ha)
0 60 90 120
2.3 3.8 4.6 4.7
Source: Syers, 1998
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The importance of phosphate fertilizer for increased crop production in developing countries The agricultural productivity of the vast area of approximately 100 million hectares of upland acid soils, originally covered by natural forests, is severely limited by P deficiency and soil acidity. On these acid upland soils soluble P fertilizers and reactive phosphate rocks increase crop yields several fold. Results obtained on rice and soybean in Indonesia, and on rice, maize, and groundnut in Vietnam with the use of soluble P and reactive phosphate rock are presented in Tables 4-a and 4-b. Table 4-a : Rice and soybean responses to water soluble P fertilizer and reactive phosphate Rock (in Indonesia) Treatments
Paddy rice (t/ha)
Soybean (t/ha)
Control TSP RPR
1.4 3.6 3.2
0.03 0.33 0.30
Source: Adiningsih, 1998
- RPR : reactive phosphate rock
Table 4-b : Rice, maize, and groundnut responses to water soluble P fertilizer and reactive phosphate rock (in Vietnam) Treatments
Paddy rice (t/ha)
Maize (t/ha)
Groundnut (t/ha)
Control SSP RPR
3.3 4.0 4.1
0.6 2.3 1.6
1.3 2.0 1.7
Source: Binh, 1998
- RPR: reactive phosphate rock
While the demand for rice in relative terms is currently diminishing in Asia, that for coarse grains, pulses, animal products and vegetables is increasing. These crops and products are best grown on the upland in this region. The above results emphasize the importance of applying phosphate fertilizers to first increase and then sustain soil fertility and hence the ability to grow good crops with rice yield above 4 t /ha, groundnut yield around 2 t/ha, and 6 t/ha of maize grain (Uexkull, 1996). Phosphorus deficiency is widespread in the WANA region and Asia given that inherently low P status is characteristic of large areas of soils. Unless P limitations to production are addressed in these regions, resource-poor farmers will continue to face low food crop production and income. In particular, in Asia, which is increasingly depending on imports of commodities such as wheat, maize, animal products, and increased phosphorus fertilization of upland soils is needed to achieve sustained and increased food production.
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The importance of phosphate fertilizer for increased crop production in developing countries FACTORS AFFECTING P FERTILIZERS EFFICIENCY The agronomic efficiency, which can be measured as yield increase per unit fertilizer input, covers at least three aspects that are application efficiency, uptake efficiency, and utilization efficiency (Krishna, 1997). Nutrient use efficiency, in particular P use efficiency, depends on the boundaries where inputs and outputs are measured: crop level, farm level and various components of the farm, landscape area, country level, etc… Unlike N, fertilizer P must be obtained by extractive mining industries and therefore its supply is finite. It should be used efficiently in agriculture to maintain P supplies to crops and minimize its loss to the environment. Among factors affecting P fertilizer efficiency are genetic variation within crop species, even between cultivars within a crop specie, form and type of fertilizer, soil characteristics and their interactions with crop grown on, and the production environment that includes technological, agroecological, and economic factors. Crop species Crops differ in their ability to take up P from the soil solution. These differences include root morphology, in particular, root length and diameter, physiological characteristics, and rhizosphere environment. These traits and characteristics are gene-governed, and the components of genetic variation for P efficiency in crops include: (1)-acquisition of P from soil, which relates to efficient root system, physiological efficiency of P uptake per unit of root length, longevity of roots, ability of roots to modify rhizosphere and enhance P availability to roots via exudation of biochemical substances; (2)-movement of P across roots and delivery to the xylem; (3)-distribution of P within plant; (4)-metabolic activity; (5)- and polyploidy and hybrid levels. Some species of crops such as lupins, canola have the capacity to significantly modify the environment of their root system, particularly under stress condition, which can increase their absorption of P several fold. They have a great production of some enzymes (citrate synthase and malate dehydrogenase) that increase the availability of soil P (Johnson et al, 1994). Development of new varieties that include traits that increase P use efficiency could impact P fertilizer application and consumption. Research is underway in most of developed countries to increase P uptake and efficiency in crops such as wheat, maize, beans, tomato, and white clover. It is focussed on utilizing genes for mechanisms to increase P uptake and efficiency. The genetic manipulation aims at altering the P concentration at the root surface and therefore the optimum soil P level for the crop. Plants can be therefore engineered to improve their P use efficiency but also their nutritional content, which can lead in many developing countries to not only increased food availability, but also to better health (Mahendra et al, 1999). Farming in major cropping zones of Asia, West Asia and North Africa is conducted under low fertility condition with soil-P deficiency as a severe production constraint. Such development can help provide optimum production levels of various crops.
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The importance of phosphate fertilizer for increased crop production in developing countries Balanced fertilizer Use The need for increased production to meet expanding food, fiber and fuel requirements of a continuously growing population is recognized worldwide. It also recognized that sustainability might include this need while addressing food adequacy in the future and the protection of the environment. Further, sustainable agriculture requires efficient management of resources, in particular, of fertilizer inputs. Increasing nutrient balances (the N: P2O5: K2O ratio) can enhance nutrient use efficiency. In many developing countries N use, in relation to P2O5 and K2O use, is excessive (Bumb et al, 1996). This reduces the efficiency of all nutrients, in particular N, and results from the tendency in many developing countries to save foreign exchange by minimizing imports of P2O5 and K2O fertilizer. But this does many harms because it reduces returns on investment in N fertilizer, leads to degradation of soils and causes environmental problems. For appropriate plant nutrition, it is essential to provide the required amount of each nutrient and establish the correct balance between the plant nutrients. Different crops need or remove nutrients from the soil in different ratios. Legumes need nutrients in ratio of 0:1:1 or1: 2:2 or 1:2:3, root crops, 2:1:2, and other crops, a ratio of 2:1:1 or 1:1:1 (PPIC, 1998). Table 5 shows the N: P2O5 ratios in 12 countries in the WANA. For many countries, these ratios indicate an imbalance in the use of P and K. In addition P2O5 applications are low, around 19 kg/ha on wheat, compared with offtake that averages 29 kg/ha P2O5 by wheat yielding 2.8 t/ha. The imbalance in P and K and low level of application of these nutrients limit crop yields, in particular under rainfed conditions, as reported in several publications from the region (Johnston, 1997). Table 5 : Ratio of N : P2O5 in 12 WANA region countries Countries Algeria Egypt Iran Iraq Israel Jordan Libya Morocco Saudi Arabia Syria Tunisia Turkey
N
P2O5
1 1 1 1 1 1 1 1 1 1 1 1
0.64 0.14 0.60 0.59 0.44 2.00 1.83 0.78 0.79 0.59 0.83 0.44
Source: Johnston, 1997
In many countries within Asia, fertilizer use is unbalanced in favor of nitrogen. This stems from the relative low cost per unit of nutrient of nitrogen fertilizers and their widespread availability. In Table 6 are presented recent N: P2O5 ratios in China, India, and Pakistan. These data show that N applications are 3 to 4 times higher than P applications. On rice this unbalance nutrient use results in lodging, greater weed competition and pest attacks, with paddy yield losses of about 20 %, but can reach 50 % under some conditions (FAO, 1995).
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The importance of phosphate fertilizer for increased crop production in developing countries Results obtained in India (Table 7) and Pakistan (Table 8) clearly show the yield and farmer’s income losses resulting to nil or low phosphorus fertilizer application compared to nitrogen. Table 6 : Ratio of N : P2O5 in China, India, and Pakistan Years
China
India
Pakistan
1991 1993 1995 1997
1 : 0.40 1 : 0.43 1 : 0.47 n.a
1 : 0.41 1 : 0.31 1 : 0.38 1 : 0.29
1 : 0.26 1 : 0.28 1 : 0.25 1 : 0.23
Sources: Xie, 1998; PPIC, 1998; and others
Table 7 : Effect of balanced N and P fertilization on the yield of some crops in Asia Crops
Rice Rice Rice Wheat Sorghum Pearl millet Chickpea Pigeonpea Cotton
Season & conditions
No. of observations
Mean yield(t/ha) without fertilizer
Unirrigated Irrigated/spring Irrigated /winter Irrigated Unirrigated „ „ „ „
380 9634 5686 10133 389 207 1325 53 55
2.4 3.0 3.2 1.6 0.6 0.5 0.8 0.3 0.3
% yield increase / unfertilization N 49 27 28 59 56 54 36 97 44
NP 74(51) 51(89) 51(82) 95(61) 92(64) 110(104) 59(64) 210(116) 91(107)
P applications (kg/ha P2O5) = 60, except on chickpea (40) N applications (kg/ha N) = 120 on rice and wheat; 90 on other cereals; and 20 on chickpea and pigeonpea (): additional increase resulting from P application
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The importance of phosphate fertilizer for increased crop production in developing countries Table 8 : Economic response to P fertilizer applications on some crops Province
N-P2O5 application 75-0 75-60
Year
Crop
Value cost ratio
Punjab
1997/1998
Rainfed wheat
Punjab
1997/1998
Irrigated wheat
120-0 120-90
3.7 (N) 3.2 (P)
Punjab
1998
Irrigated cotton
150-0 150-60
3.7 (N) 6.3 (P)
Punjab
1998
Irrigated maize
120-0 120-90
5.8 (N) 9.3 (P)
Punjab
1998
Irrigated rice
120-0 120-60
4.7 (N) 5.9 (P)
Balochistan
1998
Onions
150-0 150-100
9.8 (N) 13.3 (P)
N.. W. Frontier
1997
Sugarcane
150-0 150-75
3.3 (N) 12.0 (P)
3.2 (N) 3.5 (P)
Source: IMPHOS/FAO/NFDC project in Pakistan, 1999 N.W: North West
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The importance of phosphate fertilizer for increased crop production in developing countries P fertilization practices Phosphate fertilizer application methods can affect the efficiency of the applied phosphorus. Over several years, many application methods were tested under different cropping systems. These methods include broadcasting, banding, point placement, split applications. In Egypt and Pakistan, trials conducted on rice showed that P fertilizers are used most effectively when placed 5 cm below the soil surface (IAEA/FAO Joint Division, 1995). On maize, mixed application of N and P fertilizers at seeding increased the uptake of both P and N by 1520 %. Banding application of P resulted in higher maize yield (45 %) than broadcasting. In India, for upland crops results are overwhelming in favor of drilling and placing P below the soil surface and into the root zone (Abrol, 1998). Under irrigated conditions wheat yield increases of 400-700 kg/ha are common when P is placed or drilled compared with surface broadcasting (Tandon, 1987). In Asia, much research has defined both application methods and timing for increasing the efficiency of P. In study on fodder crop conducted in Pakistan (Alam, 1998), application of 50 kg/ha P2O5 by fertigation resulted in equivalent fodder yield as obtained by broadcasting application of 100 kg/ha P2O5. The agronomic efficiency and P fertilizer efficiency were all higher where P was applied by fertigation compared with broadcast application. Irrespective of the sources tested (Triple superphosphate, Diammonium phosphate, Urea phosphate), P applied with the irrigation water was more effective than direct soil application on tomato, sweet pepper and eggplant, in field trials conducted in Cyprus (Ristimaki et al, 1999). Yields of tomatoes increased by as much as 35 % when fertigation was employed. In line with several other studies, these results indicated that P application by fertigation is a far more efficient method than conventional soil P application. Crop management, in particular crop rotation, affected also P use efficiency. Results from China (Xie et al, 1996) showed that applying P fertilizers on the dry season crop in a rice-dry season crop rotation improved the efficiency in the forest season and increased the availability of residual P for rice. The application of P fertilizer together with organic manure results in general to increased agronomic P efficiency on rice cultivation. On heavy textured and high P fixation capacity soils, organic matter reduces soil fixation of applied P, while under other conditions it stimulates root growth, and on overall increases P uptake by crops. Application of organic matter at 4.8 t/ha, in combination with liming, on an Ultisol in West Java, improved the applied P fertilizer and increased the yield of maize from 33.5 to 56 kg grain per kg of P applied (Santoso, 1998). The appropriate assessment of crop P requirement using conventional soil testing methods or other method such as COMIFER (French Committee for Development of Rational Fertilization) approach is also of paramount importance to increasing P use efficiency. Example from IFFCO (Indian Farmers Fertiliser Cooperative) work conducted from 1992 to 1995 on 15 crops in 108 villages covering 92 districts in 14 states in India (Kumar, 1998) showed clearly the benefit associated with using soil test-based P (and other nutrients) recommendations, which increase yield and cost-benefit ratios.
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The importance of phosphate fertilizer for increased crop production in developing countries Diagnostic technique and Phosphate fertilization strategies Data from several laboratory and field experiments suggest that phosphorus is one of the most limiting nutrients to crop production in soils of the Mediterranean region. Therefore, it would be helpful to develop techniques that would enable farmers of the region to make proper use of P fertilizer to meet the demand of the plant-soil system, thereby increasing productivity and economic return. To that effect, the World Phosphate Institute (IMPHOS) in collaboration with National Agricultural Research Centers of 9 countries of the Mediterranean region set out to conduct a survey of phosphorus fertilization practices at farm level and to undertake under greenhouse a series of pot trials. The countries involved in the survey are Algeria, Egypt, France, Jordan, Morocco, Spain, Syria, Tunisia, and Turkey. Through the survey and greenhouse pot trials a mass of data was collected. With the collaboration of “Europe Sols”, a laboratory of plant and soil analyses in Toulouse-France, data processing obeyed the principles set out by the French Committee for Development of Rational Fertilization (COMIFER). COMIFER approach proceeds in two stages as illustrated in Figure 2. Figure 2 : COMIFER approach for diagnostic and prescription of phosphate fertilization recommendation
The stage of diagnosis: In order to assess soil P availability for the whole Mediterranean region, 4 parameters were considered based on the COMIFER approach: • Crop P requirement: crops were divided into three classes according to their P requirement: low, medium, and high (Table 9). • Field fertilization history: It was determined based on both the P balance at field level (P application minus crop removal) and the soil phosphorus fixing capacity. Accordingly, fields were classified as having favorable, medium or unfavorable P fertilization history (Table 10). • Crop residue management: The assumption is that all crop residues are removed from field and no P is restituted to the soil from such residues. • Soil P content: Greenhouse pot trials were used to assess plant responses to P fertilizer application over a wide range of soils of various characteristics. Two values of soil P content !
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The importance of phosphate fertilizer for increased crop production in developing countries were important to determine. The critical value (Tc) below which it is recommended to increase P application rate over the maintenance rate in order to build up soil P fertility, and the sufficient (breakeven) value (Ts) above which it is recommended not to apply any P fertilizer over a period of time. For the Tc value, Soil Olsen-P ranged from 10 to15 ppm P2O5 whereas it ranged from 50 to 55 ppm P2 O5 for the Ts value (Figure3). Figure 3 : Distribution of crop response to P application (IC
