INFLUENCE OF CONTINUOUS FERTILIZATION TO A MAIZE-WHEAT SYSTEM ON THE CHANGES IN SOIL FERTILITY

The effect of continuous application of rates of N (40, 80 and 120 kg N ha(-1)), P (0, 17.5, and 35 kg P ha(-1)) and K (0 and 33.2 kg K ha(- 1)) to a maize-wheat annual sequence on the changes in soil fertility after harvest of maize and wheat in their 11th cycle are reported. The organic carbon (O.C.), available nutrients and micronutrients tended to decline with cropping. Application of N or P significantly increase d O.C. status of the soil both after harvest of maize and wheat. Potas sium addition also increased the O.C. status but significant differenc es were observed only after wheat harvest (22nd crop). The available N status of the soil increased significantly with N application whereas a declining trend occurred with P dressings. Potassium application di d not affect the soil available N content. The maximum decline in avai lable P status was observed under N-120 P-0 K-33.2 treatment whereas a significant increase occurred in P treated plots. The available K sta tus continued to decline in plots receiving increasing rates of N and NP fertilizers. The soil available K status was maintained to its init ial content in plots receiving fertilizer K with increasing rates of N with or without P. Continuous application of increasing levels of N ( averaged over PK) depleted the soil of DTPA-extractable Fe, Mn, Zn and Cu content. The addition of P also resulted in a decline in the statu s of Mn and Cu whereas the Fe and Mn content of the soil was increased . The available micronutrients content was least affected by K additio ns. The contents of organic carbon, available N and K in differentiall y fertilized plots were higher after harvest of 22 crops (wheat) than 21 crops (maize) while the reverse occurred in respect of available P and micronutrients.