The experiment is comprised of ten nutrient management treatments viz. control, N, NP, NK, NPK, FYM, N+FYM, NP+FYM, NK+FYM and NPK+FYM with three replications. Micronutrients in soil (total and available) and in rice plant were measured. Besides, atmospheric deposition of the micronutrients in the experimental site was calculated using dust deposition and its micronutrient contents. A micronutrient balance sheet was prepared by the difference of total micronutrients output and input (Fig. 1). The results showed that application of FYM alone or in combination with chemical fertilizer increased the DTPA- Fe, Mn and Zn over control. The treatments with NPK+FYM had the highest soil DTPA-extractable Cu, Zn, Fe, and Mn after 41 years of cropping and fertilization, thus demonstrating the important role of organic manure application in improving available micronutrient status. Application of chemical fertilizers without P reduced the DTPA-Zn over the control; however, inclusion of P in the fertilizer schedule maintained it at par with the control because Zn present in the superphosphate fertilizer offset its loss due to crop harvest from the plots. Soil total Fe, Mn, Zn and Cu were significantly increased with application of P fertilizer and FYM either alone or in combination over control mainly due to their micronutrient content and atmospheric deposition. A negative balance for Zn was observed for the N, NP, NK and NPK treatments, while for remaining treatments positive balance was observed. A positive balance for Zn in control plots is due to low uptake of Zn by the rice crop and atmospheric deposition of Zn. The results of this study suggest that long term application of phosphate fertilizers, organic manures and atmospheric depositions increased the plant available micronutrient content of the soil and helped in maintaining a positive balance of iron, zinc and copper.
Mohammad Shahid, A K Nayak, P Bhattacharyya, R Tripathi,
S Mohanty, A Kumar, B Lal, Priyanka Gautam, R Raja and B B Panda
(The authors achnowledge the contribution of previous researchers invovled in this long term experiment)