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Major causes of increasing S deficiencies |
Progressively greater removal of soil S as a result of higher agricultural production (food grain production was 80 mmt in the early 1980s and 220 mmt in 2006). Sulphur removal also increases proportionately.
Increases in net depletion of soil S, not only by the removal of grain, but also by the removal of stover/straw from the field.
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Low level of fertilizer use on pulses and oilseeds that have a higher requirement of S than cereals per unit of grain production. These crops occupy . almost 27% of the gross cropped area.
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Depletion of soil S due to higher S removals as compared to S additions, resulting in severe deficitin many soils and cropping systems. At present, S uptake by crops is twice the amount of S added through fertilizers.
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A fertilizer use pattern dominated by S-free fertilizers, such as urea, DAP, MOP and S-free NP/NPK complex fertilizers. Such a product pattern not only excludes S, but accentuates its depletion resulting from the luxuriant crop produced with NPK.
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Possibility of leaching losses of soil S with the spread of flood irrigation to large areas, and in areas receiving heavy rainfall.
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Intensified agricultural production, based on increasing usage of NPK without proportionate increase in S input results in distorted nutrient ratios. In 2005, the N:S ratio in applied nutrients increased to 20 and P2O5 : S ratio to 8 against the desired ratio of 5-7:1 and 3:1 respectively.
The unbalanced consumption of N or P fertilizer in relation to S adversely affects the development of sustainable agriculture and food supply by restricting increases in crop yield, produce quality, nutrient use efficiency and economic returns. It also increases the incidence and severity of S deficiency by resulting in the depletion of soil S.
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