WATER-USE AND PRODUCTIVITY IN SUB CLOVER AND MUREX MEDIC SWARDS .1. DRY-MATTER PRODUCTION

A field experiment was established at Forbes in central-west New South Wales to investigate the hypothesis that the pattern and efficiency of water use varies between genotypes of both (Trifolium subterraneum) and murex medic (Medicago murex), and that this would affect the success of these genotypes in this environment. To test this hypothesis the productivity of two lines of M.murex (CD26 and CD53) and four cultivars of T.subterraneum (Seaton Park and Woogenellup, and two recently released cultivars, Junee and Dalkeith) were compared. Genotypes were grown both with and without irrigation and soil water was monitored for the duration of the field experiment (1987-1989). Soil water use differed little between genotypes, but when differences did occur they were related to maturity grading of the genotype with the earlier maturing cv. Dalkeith using more water without irrigation, and the later maturing cv. Junee using more water with irrigation. There was no evidence of sub. clover dry matter yield declining with time; total yield over the three years exceeded 18 000 kg/ha for all cultivars. Murex medic dry matter yields were higher than sub. clover in the year of sowing; however, dry matter yield in swards was depressed in the year following sowing and weeds contributed more to total sward yield compared to sub. clover in the third year. Both hard and soft-seeded subclover cultivars proved to be equally successful in terms of dry matter production with different cultivars performing better in different seasons and under different irrigation treatments. Sub. clover cvv. Dalkeith and Junee were able to take greater advantage of available soil water early in autumn than the other genotypes. It was concluded that water availability is not the only factor limiting sub. clover and murex medic dry matter yield in this environment.