EFFECT OF TILLAGE AND CROP RESIDUES MANAGEMENT ON MUNGBEAN (VIGNA RADIATA (L.) WILCZEK) CROP YIELD, NITROGEN FIXATION AND WATER USE EFFICIENCY IN RAINFED AREAS

A field experiment was conducted to study the effect of crop residues and tillage practices on BNF, WUE and yield of mungbean (Vigna radiata (L.) Wilczek) under semi arid rainfed conditions at the Livestock Research Station, Surezai, Peshawar in North West Frontier Province (NWFP) of Pakistan. The experiment comprised of two tillage i) conventional tillage (T1) and ii) no-tillage (T0) and two residues i) wheat crop residues retained (+) and ii) wheat crop residues removed (-) treatments. Basal doses of N @ 20: P @ 60 kg ha(-1) were applied to mungbean at sowing time in the form of urea and single super phosphate respectively. Labelled urea having 5% N-15 atom excess was applied @ 20 kg N ha(-1) as aqueous solution in micro plots (1m(2)) in each treatment plot to assess BNF by mungbean. Similarly, maize and sorghum were grown as reference crops and were fertilized with N-15 labelled urea as aqueous solution having 1% N-15 atom excess @ 90 kg N ha(-1). The results obtained showed that mungbean yield (grain/straw) and WUE were improved in no-tillage treatment as compared to tillage treatment. Maximum mungbean grain yield (1224 kg ha(-1)) and WUE (6.61kg ha(-1) mm(-1)) were obtained in no-tillage (+ residues) treatment. The N concentration in mungbean straw and grain was not significantly influenced by tillage or crop residue treatments. The amount of fertilizer-N taken up by straw and grain of mungbean was higher under no-tillage with residues-retained treatment but the differences were not significant. The major proportion of N (60.03 to 76.51%) was derived by mungbean crop from atmospheric N-2 fixation, the remaining (19.6 to 35.91%) was taken up from the soil and a small proportion (3.89 to 5.89%) was derived from the applied fertilizer in different treatments. The maximum amount of N fixed by mungbean (82.59 kg ha(-1)) was derived in no-tillage with wheat residue-retained treatment. By using sorghum as reference crop, the biological nitrogen fixed by mungbean ranged from 37.00 to 82.59 kg ha(-1) whereas with maize as a reference crop, it ranged from 34.74 to 70.78 kg ha(-1) under different treatments. In comparison, non-fixing (reference) crops of sorghum and maize derived upto 16.6 and 15.5% of their nitrogen from the labelled fertilizer, respectively. These results suggested that crop productivity, BNF and WUE in the rainfed environment can be improved with minimum tillage and crop residues retention.