Fertilizer trends in relation to biological productivity within the U. K

Abstract

Technological developments in plant and animal breeding, pesticides, veterinary products and animal nutrition, together with the use of more sophisticated machinery, have all contributed to the outstanding progress in productivity achieved by U. K. agriculture since World War II; however, the predominant factor associated with increased arable crop yields, milk and meat production from grassland has been the steady rise in N fertilizer usage. For example, wheat in 1950—52 receiving 32 kg N ha -1 yielded 2.71 t ha -1 , whereas in 1977-9 the N rate was 125 kg ha -1 and the yield 5.21 t ha -1 . Comparable figures for barley were a 1950—52 yield of 2.51, rising to 4.22 t ha -1 , with N rates of 25 and 84 kg ha -1 respectively. Winter wheat yields of over 10 t ha -1 are currently being achieved in experimental work and by some farmers in favourable seasons. Such yields, which require a total of 200 kg N ha -1 to be available from soil and fertilizer sources, have been made possible by the introduction of improved varieties. The current average farm yield of wheat, however, is only 5.21 t ha -1 , i.e. about half the potential yield. A similar situation exists with other arable crops. Similarly, the potential productivity of our grasslands is much higher than is being achieved on a national scale. N fertilizer usage on grass averages only 120 ka N ha -1 whereas experiments and practical experience have shown that the optimum economic rate is in the range 200-400 kg N ha -1 , depending on whether the enterprise is based on sheep, beef cattle or dairy cows. Biological productivity is unlikely to limit the growth of U. K. fertilizer use in the near future. Economic and political factors, such as how to use, or avoid, E. E. C. food surpluses, are likely to impose constraints long before the biological potential of crops in the U. K. is fully exploited.