Biomass allocation and nodulation of Gliricidia sepium under two cut-and-carry forage production regimes

The effects of two pruning regimes on the above-ground biomass allocation a nd nodulation of Gliricidia sepium (Jacq.) Walp. (Leguminosae: Robinieae) w ere studied in a cut-and-carry forage production system under humid tropica l conditions in Guadeloupe, French Antilles. The grass layer composed of a mixture dominated by Paspalum notatum Flugge (80%) and Digitaria decumbens Stent. The pruning regimes were partial pruning (ca. 50%) every two months and complete pruning every six months. The complete pruning caused an almos t complete turnover of N-2 fixing nodules. The nodule biomass decreased aft er the partial pruning, but the turnover was not complete. The nodule to fo liage biomass ratio followed the same pattern under both treatments, and th e values of the ratio converged towards the end of the experimental period. The maxima of standing nodule biomass were 7.2 and 13.0 kg ha(-1) in the p artially and completely pruned trees, respectively. The cumulative leaf fod der harvest was higher under partial pruning management, due to smaller lit ter loss. The branch biomass production was higher under complete pruning m anagement. Grass production was not affected by the pruning pattern of G. s epium. It was concluded that the partial pruning management produces more f odder in the studied association, and the nodulation probably adjusts to th e canopy N requirements. The potential N release to soil in the turnover of nodules of G. sepium (max. 0.82 kg ha(-1)) is negligible compared to the N export in tree and grass fodder harvest, 190 and 215 kg ha(-1) in partiall y and completely pruned plots, respectively.