Water use and productivity in sub. clover and murex medic swards. II. Seed production

Abstract

A field experiment was established at Forbes in central-west N.S.W. to investigate the hypothesis that the pattern and efficiency of water use varies between genotypes of both (Trifolium subtewaneum) 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. subtewaneum (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). Seed production in cv. Dalkeith was higher than in all other genotypes when grown with or without irrigation, and would thus be less inclined to suffer from annual legume decline than the other genotypes studied. Seed yield was very sensitive to small changes in available soil water, especially in sub. .clover cv. Junee, where water shortage over a short period during burr formation resulted in marked yield reductions. Murex medic seed yield was negatively correlated with water use. Seed size was the yield component most affected by available soil water in all sub. clover genotypes except cv. Dalkeith, where plant number was most highly correlated with seed yield. Implications for the persistence of annual legumes and the role of water use models are discussed.