Dry-matter yields and crude protein and rumen-degradable protein concentrations of three Arachis pintoi ecotypes at different stages of regrowth in the humid tropics
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abstract
Well-established stands of three ecotypes of Arachis pintoi (CIAT 17434, 18744 and 18748) were harvested from replicated plots (three blocks, each containing three plots for each ecotype) during the two dominant seasons (dry and wet) of the low altitude, humid tropics of Costa Rica. Each plot was further divided into six subplots so that, within each season, samples corresponding to 4, 6, 8, 10, 12 or 14 weeks of regrowth could be collected. For each harvest, dry matter (DM) yield of the leaf, stem and whole plant, and the leaf:stem ratio, were recorded. Samples of the whole plant were analysed for crude protein (CP), rumen-degradable (RDP) and rumen-undegradable protein (RUP) concentrations. DM yield of the leaf, stem and whole plant increased with advancing period of regrowth but the effects of period of regrowth varied somewhat among ecotypes and across seasons. Generally, DM yield was greater during the wet than during the dry season. The greatest difference between ecotypes for stem and total DM yields was evident during the dry season. In general, DM contents were low in the whole plant, leaf and stem samples (<220 g kg(-1)) and increased with increasing period of regrowth. Increases in leaf:stem ratio were most dramatic during the dry season with greater periods of regrowth, although the ratio was fairly constant during the wet season. Whole-plant CP concentration was relatively high after short periods of regrowth (up to 279 g kg(-1) DM) but declined with longer periods of regrowth; the relative decline was much greater during the dry season. The RDP concentration was relatively constant during the wet season (mean 115 g kg(-1) DM), but declined with longer periods of regrowth during the dry season (range 194-111 g kg(-1) DM). In general, the concentrations of RDP, on a CP basis, were greater during the dry season and ranged from 590 to 700 g kg(-1) CP. Season, ecotype and period of regrowth all exerted an effect on RUP concentrations.
