Indigenous Nutrient Supplying Capacity of Vertisols under Cotton and Soybean

Cotton and soybean are major crops in the region of Maharastra with vertisol soils. The current project was initiated to characterize and assess the fertility status of soils in intensive cotton and soybean growing areas of Maharashtra, to study the yield response of cotton and soybean to the addition of nutrients, and to assess the spatial and temporal variability of these nutrient responses. Fifteen on-farm trials were initiated with cotton and soybean during 2013 and 2014. The initial soil analysis of the 15 soybean sites showed that the pH varied from 7.1 to 8.1. The EC was low (0.15 to 0.33 dS/m), organic carbon (OC) was low to moderate (0.56 to 0.72%) and the CaCO₃ content ranged from 5.3 to 15.2%. The NPK fertilizer application rates applied at the soybean sites ranged from 125 to 224, 16 to 21, and 324 to 392 kg/ha, respectively. In cotton, the soil pH varied from 8.0 to 8.6 across different sites. The EC was low (0.11 to 0.43 dS/m), OC was low to moderate (0.32 to 0.79%), and the CaCO₃ content ranged from 6.7 to 16.2%.

The average grain yield of soybean recorded at 15 sites was 1.8 t/ha in the -P treatment, 2.1 t/ha in the -N treatment, 2.2 t/ha in the -K treatment, and 2.4 t/ha in adequate NPK treatments. Yield parameters were recorded at each site and plant samples were collected for nutrient uptake analysis. Post harvest soil samples have been collected at all the 15 sites for soybean. Cotton yield is assessment is in progress. The data will be used to develop a site-specific nutrient recommendation tool for cotton and soybean similar to Nutrient Expert® developed for major cereals.