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synthesis and nitrogen oxides released by their degradation. Excess nitrogen from
chemical fertilisers can pollute groundwater, but so can excess nitrogen from organic
manures.
G
On the other hand, relying solely on chemical fertilisers to provide soil nutrients without
doing other things to build healthy soil is damaging. Organic farmers don't use chemical
fertilisers, so they are very good at building soil fertility by working crop residues and
manure into the soil, rotating with legumes that fix atmospheric nitrogen, and other
techniques.
H
This generates vital soil nutrients and also creates a soil that is richer in organic matter,
so it retains nutrients better and is hospitable to the crop's roots and creatures such as
earthworms that help maintain soil fertility. Such soil also holds water better and therefore
makes more efficient use of both rainfall and irrigation water. And organic matter ties up
C02 in the soil, helping to offset emissions from burning fossil fuels and reduce global
warming.
I
Advocates of organic farming like to point out that fields managed in this way can produce
yields just as high as fields juiced up with synthetic fertilisers. For example, Bill Liebhardt,
research manager at the Rodale Institute in Kutztown, Pennsylvania recently compiled
the results of such comparisons for corn, wheat, soybeans and tomatoes in the US and
found that the organic fields averaged between 94 and 100 per cent of the yields of nearby
conventional crops.
J
But this optimistic picture tells only half the story. Farmers can't grow such crops every
year if they want to maintain or build soil nutrients without synthetic fertilisers. They need
to alternate with soil-building crops such as pasture grasses and legumes such as alfalfa.
So in the long term, the yield of staple grains such as wheat, rice and com must go down.
