Effects of sowing time and grazing on the dry matter yield, phenology, seed yield, and hardseed levels of annual pasture legumes in western New South Wales

Abstract

Fifteen annual pasture legumes [Medicago truncatula cvv. Jemalong, Cyprus, Paraggio, Sephi, Parabinga, plus fixed lines SAD 6699, SAD 6766, SAD 7883; M. aculeata lines SAD 2325, SAD 2356; M. scutellata cv. Sava; M. laciniata (cutleaf medic) local ecotype Cl2; Trifolium subterraneum cvv. Nungarin, Dalkeith, Seaton Park] were sown at Condobolin at 6 times in autumn and winter 1986 and periodically grazed at 3 levels of intensity (nil, until flowering, until pod formation). Late sowing greatly reduced (P<0.001) the weight of 50-day-old plants, more so for some varieties (e.g. Cyprus) than others (e.g. Dalkeith, SAD 2325). Seed size accounted for most of the variation (R2 = 0.92) in the weight of plants with 1-2 trifoliate leaves. Total dry matter yields were reduced (P<0.001) by later sowing and grazing, and there were interactions between both of these factors and variety. The subterranean clovers yielded most dry matter and Cyprus and Sava least. Dry matter yields of SAD 6699 and cutleaf medic were reduced least by grazing. Time from sowing until flowering was shorter with later sowing times. With later sowing times, the order of flowering of early-maturing varieties changed, and the difference between the earliest and latest varieties fell from 100 to 11 days. Grazing delayed flowering by up to 2 weeks. All treatments and interactions affected (P<0.001) seed yield. Seed yields were highest (>100 g/m2) in ungrazed early-sown plots and were reduced (P<0.001) at later sowing times by grazing until pod formation for all sowing times for all varieties, and by grazing until flowering for some varieties. Cutleaf medic, Nungarin, and Dalkeith had superior seed yields under adverse conditions of grazing and late sowing. Spring dry matter yields accounted for 90% of the variation in seed yields. There was no optimum dry matter yield for maximum seed yield (except SAD 7883 at 778 g/m2 and cutleaf medic at 275 g/m2) under mild spring conditions, and flowering time did not account for variation (P>0.05) in seed yields at any sowing time. Seeds on previously ungrazed plots progressively softened between 8 December 1986 and 8 March 1987, with those of Jemalong, Cyprus, Parabinga, SAD 6766, cutleaf medic, Dalkeith, and Seaton Park softening more rapidly on later sown plots.