Impact of Continuous Use of Inorganic Fertilizers and Organic Manure on Soil Properties and Productivity under Soybean-Wheat Intensive Cropping of a Vertisol

The status of nutrients – their depletion and build-up in soil, and crop productivity after thirty-six years (1972–73 to 2008–09) of intensive cropping were studied under continuous use of various inorganic fertilizers and organic manure in a Vertisol. Results showed that the application of recommended dose of N, P and K (20:80:20 kg ha−1 to soybean and 120:80:40 kg ha−1 to wheat) with organic manure @ 15 t FYM ha−1 resulted in 145 and 292% increase in soybean and wheat yields, respectively over control. Conjoint use of FYM with 100% NPK substantially improved the organic carbon status by 3.9 g kg−1, as well as available N, P and S by 126.8, 25.5 and 28.5 kg ha−1 in soil over its initial values, thereby indicating significant contribution towards sustaining the soil health. On the other hand, omission of S in 100% NPK–S treatment caused a continuous depletion (5.8%) in soil S status over initial value. A declining trend (179 to 314.8 kg ha−1) from its initial value (370.0 kg ha−1) of available K status was also observed as a result of continuous cropping; this indicates considerable mining of available K from the soil. However, the decline of K was of lower magnitude with 100% NPK+FYM (14.9%) and 150% NPK (20.0%) treatments indicating the need to raise the level of K fertilizer application to meet the demand of crops. However, the fertility of the soil appears to be adversely affected due to the imbalanced use of nutrients viz., NP or N alone. Thus, the balanced use of fertilizers continuously either alone or in combination with organic manure is necessary for sustaining soil fertility and productivity of crops.