EFFECT OF PLANT RESIDUE AND FERTILIZER ON GRAIN-YIELD OF DRYLAND RICEUNDER REDUCED TILLAGE CULTIVATION

Use of reduced tillage practices and inputs of organic materials, rath er than chemical fertilizers, has been suggested as a method of 'low i nput agriculture' to achieve sustainability in dryland agriculture. Th is study evaluated the effects of incorporation of plant residue and c hemical fertilizer under reduced tillage on biomass and grain yield of dryland (rainfed) rice (Oryza sativa L.). Four treatments were establ ished: (a) a no-input control; (b) chemical fertilizer 80 kg N ha(-1), 40 kg P ha(-1), and 30 kg K ha(-1); (c) air-dried wheat straw (organi c C 378 g kg(-1), total N 4.8 g kg(-1), total P 0.9 g kg(-1), C/N rati o 75.5) at 20 Mg ha(-1) (the amount of N in straw was equivalent to th at applied with chemical fertilizer); (d) wheat straw + fertilizer, st raw applied at 10 Mg ha(-1) and rate of fertilizer 50% of (b). The soi l type at the site is a Inceptisol and, a silt loam, pH 6.7 and water holding capacity 405 g kg(-1). Straw and fertilizer treatments were ap plied about 3 weeks before planting. Inorganic N (nitrate+ammonium-N) concentrations in the control, fertilizer, straw, and straw+fertilizer amended soils were 7.2, 11.6, 8.6 and 11.5 mu g g(-1), respectively. Available P was greatest in the straw+fertilizer treated plots (16.7 m u g g(-1)) followed by fertilizer (16.0 mu g g(-1)), straw (14.2 mu g g(-1)) and the control (12.0 pg g(-1)). The rates of N-mineralization in the straw C fertilizer, fertilizer and straw treatments were 16.6, 14.3 and 11.2 pg g(-1) month(-1), respectively. Microbial biomass C, N and P were 66, 77 and 49% greater, respectively, in the straw+fertili zer treated plots than in the control. Total crop biomass ranged from 6.79-9.91 Mg ha(-1) and grain yield ranged from 1.08-1.46 Mg ha(-1), b oth in the order: control<straw<fertilizer<fertilizer+straw. There wer e strong positive relationships between grain yield and microbial biom ass (r= 0.84, P<0.001), N-mineralization (r=0.85, P<0.001), and availa ble P (r=0.84,P<0.001). The combined input of straw and fertilizer cou ld be an ideal practice to improve soil fertility and thereby the prod uctivity of rice under dryland (rainfed) conditions.