COMPARISON OF NITROGEN, PHOSPHORUS AND POTASSIUM UTILIZATION EFFICIENCY IN MAIZE MUNGBEAN INTERCROPPING

Effects of rhizobial inoculation and applied nitrogen on the utilization efficiency of N, P and K were studied in relation to the yield advantage in additive maize/mungbean intercrops at Los Banos, Philippines in 1988. Inoculation increased grain yield of both maize (Zea maya L.) and mungbean (Vigna radiata (L.) Wilczek). Yield of maize increased by 60% in the sole crop and 71% in the intercrop as the N application rate was increased from 0 to 90 kg/ha, with a corresponding decrease of 29-35% in the yield of the associated mungbean. Intercropping reduced mungbean yield by 35-57%; maize was less affected. Inoculation also improved the land equivalent ratio (LER). The highest LER (1.49) was obtained at 30 kg N/ha with inoculation. Nutrient absorption by both maize and mungbean was reduced due to intercropping, mungbean being more affected than maize. The reductions in the N absorption efficiency of maize ranged from 4 to 37% and those of mungbean from 37 to 58%. Increases in N rate increased N absorption of maize but caused greater reductions in N absorption of mungbean. Reductions in P absorption by intercropped maize declined with increases in applied N and with inoculation. Inoculation, however, had a lesser effect on K absorption efficiency. Land equivalent ratio analysis in terms of N, P and K utilization efficiency showed that the increase in LER over unity was due largely to a higher total uptake of nutrients by the component crops in the mixture than by the sole crops. The greater efficiency of intercrops than of the sole crops in converting absorbed nutrients to grains also contributed to the yield advantage.