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 increased O.C. status of the soil both after harvest of maize and wheat. Potassium addition also increased the O.C. status but significant differences 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 did not affect the soil available N content. The maximum decline in available 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 status continued to decline in plots receiving increasing rates of N and NP fertilizers. The soil available K status was maintained to its initial 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 status of Mn and Cu whereas the Fe and Mn content of the soil was increased. The available micronutrients content was least affected by K additions. The contents of organic carbon, available N and K in differentially 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.