Effects of harvest management and nitrogen application on yield and nutritional value of Rhodes grass and lucerne in pure stands and mixtures

Abstract

Rhodes grass (Chloris gayana Kunth), lucerne (Medicago sativa L.), and their mixtures in different seed proportions were sown in a replacement series in two successive years and the effects of seed proportion, N level (0, 46, 92, or 138 kg ha-1 yr-1), and harvest management (three or two cuts year-1) on yield and nutritional value during four years of growth were studied. Overall, there was no significant dry matter (DM) yield difference between the three-cut harvest management (A) and the two-cut harvest management (B), but the former was superior during years of favourable rainfall. Nitrogen application of 138 kg ha-1 yr-1 improved the DM yield of Rhodes grass and mixtures by 102 and 57%, respectively, compared to no nitrogen. Dry matter yields of mixtures exceeded that of Rhodes grass (the high-yielding monoculture) by 22% without N application but at high N application the yield difference between the grass and mixture was small. Crude protein (CP) concentration and yield and metabolizable energy (ME) in mixtures were higher than that of Rhodes grass by 61, 104, and 11%, respectively. The contents of both CP and ME were positively correlated with the proportion of lucerne in the mixtures but the correlation coefficients were lower at high N application. The advantage of mixing lucerne with Rhodes grass was mainly to improve the nutritional value of the herbage. It is concluded that Rhodes grass - lucerne mixture should be planted at 1.2 and 5 kg ha-1 pure germinating seed, respectively, and the mixtures should be cut at least three times a year.