Summer forages under irrigation. 4. The growth and mineral composition of forage legumes

Abstract

Summer forage legumes from the species Vigna unguiculata, Macroptilium lathyroides, Lablab purpureus, Arachis hypogaea and Glycine max were grown under irrigation at Trangie, New South Wales. Dry matter accumulation and plant development were recorded in primary growth and three subsequent regrowths. Plant fractions were analysed for nitrogen, sulfur and sodium during primary growth. In primary growth lablab produced the highest dry matter yield of 14 t/ha. This was attributed to very late flowering (110 days) and woody stems able to support this bulk. In contrast, cowpea lodged after producing 7 t/ha. Soybean produced 10 t/ha of dry matter but rapid leaf abscission detracted from its forage potential. Phasey bean was an excellent species under a 6-week cutting regime, yielding 10 t/ha from four cuts. In contrast to other species, it branched rapidly and extensively from basal buds. The basal branching and prostrate growth habit of peanut enabled it to yield 9 t/ha from three cuts. The leaves of all species contained over 3% nitrogen; mature stems had only half this concentration. Phasey bean and cowpea had much higher sodium contents (1040 and 1535 ppm at 10 weeks) than lablab (335), peanut (80), and soybean (165), the latter three being below recommended levels for animal production. All species contained satisfactory levels of sulfur (0.21, 0.30, 0.20, 0.18 and 0.17% in phasey bean, cowpea, lablab, peanut and soybean, respectively, at 10 weeks).