Productivity and soil fertility changes under continuous fertilization of rice (Oryza sativa) -rice cropping system

A long-term experiment in an Udic Ustochrepts soil with rice (Oryza sativa L.)-rice cropping system was conducted during 1987-96 at Hyderabad to evalu ate the effect of continuous cropping and fertilization on yield and soil f ertility. Maximum doses of fertilizer @ N-120 and P-80 had increased grain yield by about 0.6 to 0.7 tonne more compared to N-40 or no P2O5. Potash ap plication @ K-40 kg/ha showed a meagre response. Net returns for the croppi ng system were maximum (Rs 13 180/ha) at N120P80K40. Stability analysis of grain yield indicated that consistent productivity is possible with N80P40K 0 both in rainy season (kharif) and winter season (rabi). After 10 consecut ive years of cropping, available phosphorus and Potassium got depleted comp ared to their initial status. Available iron, zinc,pore space, water holdin g capacity and volume expansion showed increase over their initial values a fter 20 seasons of cropping. The trends clearly emphasised the need for bal anced fertilization of rice for consistent productivity.