Optimum legume proportion for plant and animal production in a subtropical grassland

Abstract

Integrating legumes into grass pastures is an alternative to nitrogen (N) fertilizer for improving productive, economic, and environmental performance of grazing systems. However, optimal legume proportion for maximizing resource-use efficiency in mixed pastures is seldom considered. Here, we studied the effect of rhizoma peanut (Arachis glabrata Benth.) proportion in bahiagrass (Paspalum notatum Flügge) pastures on herbage accumulation and nutritive value, cattle selectivity, and animal gain using a Bayesian probabilistic approach for 2 years. Two 0.5-ha bahiagrass monoculture pastures receiving no N fertilizer and six 0.5-ha bahiagrass-rhizoma peanut pastures (16.5%–49.2% legume) were continuously stocked at a herbage allowance of 1.5 kg dry matter (DM) kg⁻¹ animal live weight. Regressing plant and animal production on legume proportion in the pasture, we found that responses increased non-linearly and were maximized at ∼40% legume. Herbage accumulation was maximized at 39% legume, being 173% greater than the bahiagrass monoculture (9.0 vs. 3.3 Mg ha⁻¹ DM). At 39% legume, herbage in vitro digestible organic matter and crude protein concentrations were 543 and 136 g kg⁻¹, respectively, 43% and 84% greater than at 0% legume (381 and 74 g kg⁻¹, respectively), and legume in cattle diets was 20 percentage units greater than offered. These data explain in part why average daily gain and gain per hectare were maximized at ∼36% legume, being 108% (604 vs. 290 g day⁻¹) and 127% greater (350 vs. 154 kg LW ha⁻¹) than for animals grazing the monoculture. In conclusion, legume proportions of 30%–40% maximized plant and animal production of this subtropical grassland.