Grain yield of wheat in rotation with pea, vetch or medic grown with three systems of management

Abstract

Pea (Pisum sativum L. cv. Alma), vetch (Vicia sativa L. cv. Languedoc) and annual medic (Medicago truncatula Gaertn. cv. Paraggio) were grown at Brinkworth, South Australia, in 1987 in large (0.75 ha) plots and subjected to 3 systems of management: (i) ploughing in at flowering as a green manure crop, (ii) harvesting for grain and ploughing in the dry residues, and (iii) harvesting for grain and removing the residues. A wheat crop was sown over the whole area in the following season (1988) and the effects of type of legume and management on grain yield and grain protein content were measured. The management system imposed on the legume had a highly significant (P<0.01) effect on the grain yield of the following wheat crop, but there were no significant differences between the 3 legumes in their effects on wheat yield or on grain protein content. Ploughing in the legumes as a green manure crop at flowering added about 100 kg/ha more nitrogen (N) to the soil than allowing the legumes to mature, harvesting for seed, and removing residues. Incorporating the dry residues rather than removing them added about 26 kg N/ha. The green manure crop significantly increased subsequent wheat yield (by 49%; P<0.001) and protein content of the grain (by 13%; P<0.05) compared with the treatment in which the legumes were harvested for grain and all residues removed; incorporating the dry residues increased yield by 10%. It is concluded that the amount of N added during the legume phase in a rotation is more important than the kind of legume from which the N is derived. The occasional use of a dense legume crop as a green manure may rapidly add a large amount of N to a soil to be slowly exploited by following grain crops.