Residual effects of growing mungbean and uridbean on the yield and nitrogen uptake of a succeeding wheat crop

A two year field experiment was carried out at the Indian Agricultural Research Institute, New Delhi-110012, India to assess the effect of mungbean (Vigna radiata L.) and uridbean (Vigna mungo L.) residues on the yield and N uptake of a succeeding wheat crop as compared to sorghum fodder. Sorghum produced 3.5-7.5 times more dry matter and removed 2-3 times more nitrogen than mungbean or uridbean during same duration (80 +/- 10 days) of their growth. Without N application the grain yield of wheat following mungbean and uridbean (without residue incorporation) was 0.45 and 0.48 t ha-1 more than the yield of wheat following sorghum fodder. These yields were equivalent to that predicted when 36 and 38 kg urea-N ha-1, respectively, was directly applied to wheat. The residual effects of these grain legumes were higher when succeeding wheat was fertilized with 60 kg urea-N ha-1; at this level mungbean and uridbean spared 52 and 43 kg urea-N ha-1, respectively, in succeeding wheat. The residual effect of mungbean and uridbean further increased when their residue was incorporated in soil; with this practice they spared 94 and 115 kg urea-N ha-1, respectively, without N application to wheat and 74 and 82 kg urea-N ha-1, respectively, with an application of 60 kg urea-N ha-1 to wheat. Mungbean and uridbean, without residue incorporation, increased aboveground plant-N uptake of succeeding wheat by 11.5-34.9 and 10.8-34.0 kg N ha-1, respectively; whereas with residue incorporation, they increased aboveground plant-N content of succeeding wheat by 26.1-45.8 and 32.7-47.7 kg N ha-1, respectively. The results of the present study indicate that there is both an indirect 'sparing' effect and a direct residual effect of mungbean and uridbean on the nitrogen needs of succeeding wheat, more so when their residues are incorporated in soil.