Forage Growth Performance Of Lablab Bean In The Semi-Arid Tropics

Lablab bean {Ixiblab purpureas (L.) Sweet) is a fast-growing, short-term perennial, tropical legume with a myriad uses for food, feed and green manure. The primary objective of this study was to determine clipping management practices required for optimizing hay and nitrogen yields of the lablab cultivar Rongai in the dry Caribbean. A secondary objective was to compare agronomic trails of eight introduced lablab bean accessions. Plots of lablab bean established on an alkaline fpH>7.8) clay soil (fine carbonitic, isohyperthermic, Typic Rendolls Mollisols) were initially harvested at one of four physiological stages of growth: vegetative (VGT), first visible inflorescence (FVI), full bloom (FB) and green pod (GP) to a 15-cm stubble height. The experimental design was a randomized complete block with three replicates. A subsequent forage harvest was taken at the green pod stage of growth for all treatments because of the propensity of lablab bean to flower early in the cool, shortday photoperiod between the months of December and March, Forage subsamples were processed for leaf/stem ratio and overall dry matter (DM) yield determination. Another subsample was separated into two sequential 15-cm fractions and a top vertical fraction beginning from the base of harvested forage. All forage fractions were dried and analyzed for crude protein (CP). Forage DM yield from the initial harvest followed a typical sigmoid growth curve. It increased from 1,180 kg/ha at the VGT to 3,440 kg/ha at the GP stages of growth. Average DM yield from the aftermath was only 588 kg/ha, regardless of the initial harvest treatment, because of drought and a shorter photoperiod. The leaf fraction constituted 60 and 50% of forage DM for the first three and the GP stages of growth, respectively. Mean leaf CP was 25% and independent of maturity. However, stem CP decreased from 11 to 7% in the initial harvest with maturity but remained constant at 11 % in the aftermath. The basal 15-cm forage fraction constituted 17% of total DM at the VGT but 9-13% at the reproductive stages of plant growth. The upper two fractions (83-91% of forage DM) exhibited CP contents between 15 and 25%. The results suggest that approximately 3,500 kg/ ha of lablab hay with 20% CP content is obtainable in a very dry season. For dual seed and forage production, Rongai was simitar to the best introduced accessions. However, individual lablab bean accessions exhibited either higher seed or forage production than Rongai. More experiments are being conducted to determine lablab performance under favourable rainfall conditions in the Caribbean.