Evaluation of N2fixing cover legumes as green manures for N substitution in coconut Cocos nucifera Linn palm 13

A field experiment was conducted in an adult coconut (Cocos nucifera Linn.) plantation in an acidic laterite soil type to test the feasibility of partially substituting fertilizer-N with the N contributed by cover legume-Rhizobium system when grown as green manures in a coconut basin. The treatments included in situ cultivation and incorporation of two leguminous creepers, Mimosa invisa and Calopogonium mucunoides in a 1.8-m radius basin area surrounding the palm, with inorganic N doses of 250 g and 375 g and a control (devoid of legume) with 500 g N palm -1 supplied as urea. Mimosa invisa and C. mucunoides produced 20.5 kg and 12.8 kg of above-ground wet biomass and 134.8 g N and 70.0 g N basin -1 , respectively, when harvested after 140 days growth for incorporation. Higher N 2 -fixation efficiency was shown by M. invisa as evidenced by nodule biomass and acetylene reduction activity of the nodulated root system. Analysis of the coconut basin soils revealed a trend towards higher N in legumes + 375 g N treatment and K in Calopogonium treatments, and microbial biomass and dehydrogenase enzyme activity in integrated treatment of legume biomass and fertilizer-N when compared to that of the control. The yield data of coconut palms collected over a period of four years indicated the possibility of substituting 50% fertilizer-N with the N contributed by the leguminous crops.