Effects of initial clover seeding rate and length of ley on pasture production, soil nitrogen and crop yields in a ley farming system

Abstract

Several factors relating to the use of subterranean clover (Trifolium subterraneum) in a ley farming system were studied at Kojonup in the south-west of Western Australia viz; the effect of seeding rates of clover on the botanical composition and herbage production of a grazed pasture over five years; the build-up of soil nitrogen over this period, and the effect of 5, 8 and 11 years of clover on wheat yield and on subsequent regeneration of the pasture. In the final year (year 12) the effects of lime on mineralization of soil nitrogen and on crop yields were also studied. Seeding rates of clover in excess of 6 kg ha-1 affected botanical composition in the first year, and yield of pasture in the first two years only. Build-up of soil nitrogen over the first five years (when all plots were grazed) was significantly greater (P < 0.05) where clover had been sown at the higher rates (< 6 kg ha-1) but this did not result in increased wheat yields at the end of this period. In the 12th year, when all plots were cropped, there were no significant differences in grain yield between treatments cropped for the first time (after 11 years of clover) and those cropped either once or twice in the preceding six years. Cropping reduced pasture production in the early part of the post crop year but the proportion of clover in the pasture increased. The application of lime (in year 12) resulted in a significant increase in grain, and straw yields and nitrogen uptake on all treatments. The results suggest that crop yields can be sustained in short term rotations provided there is sufficient clover present in the pasture phase.