Dry matter yield of dryland and irrigated mixtures of Caucasian clover, white clover and perennial ryegrass over 5 years at Lincoln University

Abstract

This experiment investigated the effects of Caucasian clover (CC), white clover (WC), perennial ryegrass (RG) and their mixtures on dry matter (DM) yield under dryland and irrigated conditions over 5 years (1st July-30th June) at Lincoln University. Seven mixtures of the three species (three pure, three binary and one ternary) were sown in November 1999, grown with and without irrigation, and grazed by sheep. Total annual DM yield in Years 2-6 (2000/2001-2004/2005) was analysed. Clover-RG mixtures yielded more than the average monoculture yields of their constituent species (over-yielding). This diversity effect was 1.8-7.0 t DM/ha for WC-RG over all 5 years and 2.7-4.6 t DM/ha for CC-RG in Years 3-6. There was no additional yield benefit from the three-species mixture. Diversity effects were due to synergistic interactions between the clovers and RG, which were similar for CC and WC once established. The interspecific interactions persisted despite changes in botanical composition across irrigation levels and years.