Evaluation of N2-fixing cover legumes as green manures for N substitution in coconut (Cocos nucifera Linn.) palm. (13)
Keywords:Coconut palm, Cover legumes, Green manures, Nitrogen substitution
AbstractA 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 of 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 N2-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.