Effects of subterranean, rose and cupped clovers on soil nitrogen and on a subsequent cereal crop

Abstract

Three annual clover species : subterranean clover, Trifolium subterraneum (cv. Geraldton), rose clover, T. hirtum (cv. Kondinin), and cupped clover, T. cherleri (cv. Yamina) were compared for yield of dry matter, for their effects on soil nitrogen, dry matter yield, and nitrogen uptake by a subsequent cereal crop. In one experiment, the three clover species and annual ryegrass (Lolium rigidum), were grown in lysimeters to provide measurements of dry matter and nitrogen yields of plant tops and roots. Half of the lysimeters, from which the plant roots had not been removed, were later sown with wheat. Rose clover produced the highest yield of root nitrogen, and this was reflected in higher nitrogen uptake in the succeeding wheat crop. Nitrogen yield of wheat after ryegrass was 60% of the average yield after clovers. The three clover species were also included in a pasture experiment, which was grazed by sheep for five years. Samples were taken from the field plots to provide soil for a glasshouse pot experiment, and for chemical analysis. In the pasture experiment, build up of soil nitrogen over six years did not differ significantly between the subterranean and rose clover treatments, although there were large differences in clover plant numbers and herbage production, and botanical composition of the pastures. However, inorganic nitrogen concentrations were much higher in soil from the subterranean clover plots than in soil from the rose or cupped clover plots, particularly in the later stages of the field experiment. Total nitrogen increase and mineral nitrogen concentration were lowest in soil from the cupped clover plots, although herbage yield was comparable with that of rose clover