Influence of continuous cropping and fertilization on nutrient availability and productivity of an alluvial soil

The status of soil nutrients, their depletion or build-up and crop productivity after a twenty-three years of intensive rice-wheat cropping under various fertilizer treatments was studied. In general, yields of both rice and wheat started declining after ten years of cropping. Omission of P fertilizer accelerated the decline in yields. Continuous application of N and K fertilizers revealed a marginal change in soil available N and K over time, but about 3- and 2- fold increase in available P and S, respectively, were observed by regular application of P fertilizer (SSP: 7% P, 12% S) over 23 years. The status of organic carbon increased in all the treatments except control plots. There was a general reduction in the contents of DTPA extractable Zn, Cu and Mn. However, there was overall increase in the DTPA-Fe over the years where the plots received single superphosphate. The combined effect of deficiency of P, K, S and Zn, toxicity of Fe and imbalances due to antagonisms between P-Zn, Fe-Zn and S-Zn seemed to be responsible for the decline in the productivity of rice and wheat. Balanced and high doses of NPK fertilizers and inclusion of S and Zn in fertilizer schedule are required to maintain soil fertility and sustain grain yields in the long run.