Fodder grass productivity and soil fertility changes under four grass plustree associations in Kerala, India

Adapted tree+grass combinations make a valuable contribution to forage prod uction in the Indian peninsula, but knowledge of the interactive effects be tween trees and grasses on their production is limited. We, therefore, cond ucted a field experiment involving combinations of four trees and grasses, besides monospecific grass controls, for seven years, to investigate grass productivity in association with leguminous and non- leguminous multipurpos e trees (MPT) having disparate canopy architecture, and to assess the end-o f-rotation soil fertility changes. Post rotation changes in herbage product ivity were evaluated by growing teosinte (Zea mexicana) for three years. Th e four MPTs were Acacia auriculiformis, Ailanthus triphysa, Casuarina equis etifolia and Leucaena leucocephala. Grasses included Pennisetum purpureum ( hybrid napier), Brachiaria ruziziensis (congo signal), Panicum maximum (gui nea grass) and teosinte. Lower tree branches were pruned from fifth year. U nderstorey herbage production increased until three years in all tree+grass combinations, but declined subsequently, as tree crowns expanded. Overall, casuarina among MPTs, and hybrid napier and guinea grass among forage crop s, were more productive than others. Pruning MPTs generally favoured greate r herbage production. Understorey light levels for acacia, ailanthus, casua rina and leucaena were 17, 60, 55 and 55% of that in the open at five years . During the post-rotation phase, MPT plots were characterised by higher so il nutrient capital and consequently teosinte yields were higher than in th e treeless control treatment. All previous tree-grass combinations showed a n increasing trend till two years after MPT felling. Yield levels declined subsequently, despite at variable rates. Careful selection of the tree and grass components is, therefore, crucial for optimising herbage productivity in silvopastoral systems.