The energy costs of the nitrogen fertilisers used in Britain, the returns received and some savings that are possible

Published estimates suggest that one‐third of the energy used in many intensive mechanised systems of arable agriculture is required to produce the nitrogen fertilisers used. The increases in yield that nitrogen fertilisers give in Britain are very profitable to farmers although prices of N are nearly twice those of two years ago. Some of the nitrogen involved in intensive agricultural systems is lost. Losses of nitrate by leaching can be diminished by greater care in timing the application of nitrogen fertilisers. Denitrification, which results in loss of nitrogen and its oxides, is diminished by careful management of soil and crop wastes. Losses of ammonia may be lessened by better handling of organic manures. Nevertheless some loss of nitrate by leaching in winter is inevitable, as is loss of ammonia from animal excreta. Farmers can use fertilisers more efficiently by fitting the amounts applied more closely to local conditions of soil, previous cropping and manuring and to the weather. Increased use of leguminous crops and more efficient use of organic manures will diminish the need for nitrogen. But it is not possible to achieve large yields of non‐leguminous crops by relying solely on nitrogen from “natural” sources; fertilisers are essential in modern intensive agriculture.