[PDF Notes] Short essay on Fertilizers and Sustainability of Agriculture

For the last three decades all over the developed world fingers have been raised on fertilizers, particularly nitrogen, as the number one enemy of sustainable agriculture. One should not be surprised to see this happen if the rates of application are too high such as in Netherlands.

Nitrogen is a mobile nutrient both in plants and soils and considering the fact that its efficiency (nitrogen taken up by the above ground portion of crop expressed as percentage of that applied) varies from 30 per cent to 40 per cent in rice and 60 per cent lo 80 per cent in other cereals, a sizeable amount could be added to the environment as ammonia by volatilization from soil surface, nitrous oxide or elemental nitrogen by denitrification which is not restricted to tropical rice regions, but also applies to temperate regions and finally as nitrates by leaching in underground water.

The ammonia going in the atmosphere contributes to acid rain, while involved in depletion of the ozone layer. What one generally overlooks is that in the case of nitrogen fertilizers, we recycle atmospheric nitrogen, which is the raw material for ammonia and urea manufacture.

At least 30 per cent to 50 per cent of it is converted into human edible food and about one-third is immobilized in the soil and only the rest goes back to the atmosphere either as ammonia or as N, 0 or N, after denitrification of nitrates.

Phosphates which are not so mobile in soil and get fixed in the soil as insoluble compounds could also leach from very light soils and may also move with eroded surface soil to surface waters such as lakes and ponds.

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