PERFORMANCE OF WHITE CLOVER PERENNIAL RYEGRASS MIXTURES UNDER CUTTING

Clover persistence in mixtures of two varieties of perennial ryegrass (Lolium perenne) with contrasting growth habits and three white clover (Trifolium repens) varieties differing in leaf sizes was evaluated at two cutting frequencies. An experiment was sown in 1991 on a clay soi l. The plots received no nitrogen fertilizer. In 1992, 1993 and 1994, mixtures containing the large-leaved clover cv. Alice yielded signific antly more herbage dry matter (DM) and had a higher clover content tha n mixtures containing cvs Gwenda and Retor. Companion grass variety di d not consistently affect yield or botanical composition. Cutting at 2 t DM ha(-1) resulted in slightly higher total annual yields than cutt ing at 1.2 t DM ha(-1), but did not affect clover content. In 1992 the mixtures yielded, depending on cutting frequency and variety, 10.6-14 .6 t DM ha(-1) and 446-599 kg ha(-1) N, whereas grass monocultures yie lded only 1.2-2.0 t DM ha(-1) and 25-46 kg ha(-1) N. From 1992 to 1994 the annual mean total herbage yield of DM in the mixtures declined fr om 12.2 to 10.5 to 8.7 t ha(-1), the white clover yield declined from 8.7 to 6.5 to 4.1 t ha(-1) and the average clover content during the g rowing season declined from 71% to 61% to 46%, whereas the grass yield increased from 3.4 to 4.0 to 4.5 t ha(-1). The N yield decreased from 507 to 406 to 265 kg N ha(-1) and the apparent N fixation from 470 to 380 to 238 kg N ha(-1). Nitrate leaching losses during the winters of 1992-93 and 1994-95 were highest under mixtures with cv. Alice, but d id not exceed 10 kg N ha(-1). The in vitro digestible organic matter ( IVDOM) was generally higher in clover than in grass, particularly in t he summer months. No differences in IVDOM were found among clover or g rass varieties. The experiment will be continued to study clover persi stence and the mechanisms that affect the grass/clover balance.