Biological nitrogen fixation and grassland production in the United Kingdom

• Published in: Philosophical transactions of the Royal Society of London. Series B, Biological sciences Biological sciences, 1982-01, Vol.296 (1082), p.397-404
• Main Author: Cowling, D.W
• Format: Article
• Language: English
• Subjects: Agriculture and the Nitrogen Cycle; Clover; Crops; Fertilizers; Grasses; Grassland soils; Legumes; Nitrogen; Nitrogen fixation; Sward; Symbiosis
• ISSN: 0080-4622; 0962-8436; 1471-2970; 2054-0280
• DOI: 10.1098/rstb.1982.0015

Grassland occupies almost two-thirds of the agricultural land in the United Kingdom; it has a varied botanical composition and sometimes includes legumes that fix N2. Estimates of the amount of N fixed have been made in field experiments; for mixtures of white clover with grass it varies from 74 to 280 kg ha-1 annually, and for crops of red clover and lucerne it is at the higher end of that range. The contribution from white clover and other legumes sown with grass declines markedly with increasing addition of fertilizer N. In agricultural practice, white clover is rarely a major constituent of swards, reflecting a 30-fold increase in the use of fertilizer N during the last 35 years, and it is estimated that the average amount of N fixed annually is 11 kg ha-1. The areas sown to red clover and lucerne are small and are declining. Experimental data suggest that fixation by free-living organisms is much less than fixation by legumes. In practice the contribution from fixation may be improved by more careful culture of white clover in swards, and by an increased use of leguminous forage crops to provide conserved feeds.