The effects of cutting frequency on yield of Hunter River lucerne grown at wide and close spacing in the Mediterranean climate of South Australia

Abstract

Hunter River lucerne, sown in April, June, and August, was planted out at 60 cm X 60 cm or 20 cm X 20 cm spacings on a red brown earth soil. Plants were cut 2.5 cm above ground level every six to eight weeks (standard cutting), or twice as often (frequent cutting), for two years : the yield of dry matter and number of stems per plant were measured at each cut. Yields were smallest in late summer and autumn, and largest in late spring and early summer. Treatments generally had little effect on the seasonal growth rhythm. Frequent cutting nearly always decreased yields. The relative decrease was greatest when standard cut plants were growing most rapidly in late spring, and it was also greater with wide spacing than close spacing. Wide-spaced plants yielded more per plant, and less per unit area, than close-spaced plants, except in late summer. Sowing time influenced yield only until the middle of the first summer. Number of stems per plant, and the mean weight of each stem, were both smallest in autumn and winter, and largest in spring and early summer. Frequent cutting slightly, and increasingly, decreased stem numbers relative to the number present with standard cutting during the experiment. The number of stems per plant was largest, and generally increased throughout, at wide spacing, whereas at close spacing maximum stem numbers were attained in the establishment year. Weight per stem showed greater seasonal variation than numbers. Low winter yields and low yields with frequent cutting could both be largely attributed to the small stem weights. Some implications of these results for lucerne management, and breeding for yield improvement, are discussed.