Effect of Long-term Application of Organic, Inorganic and Integrated Nutrients on Soil Potassium Fractions in a Vertisol of Central India

The present study was conducted at the experimental field of College of Agriculture, Indore during 2018-2019.Soybean (cv. JS-9305), was grown with 80 kg ha-1 seed rate with row to row and plant to plant spacing of 40 cm X 5 cm. Soybean crop was grown as per standard cultural practices. The experiment was conducted with nine treatments viz., T1- unfertilized control, T2- 20 kg N + 13 kg P ha-1, T3- 30 kg N + 20 kg P ha-1, T4- 40 kg N + 26 kg P ha-1, T5- 60 kg N + 35 kg P ha-1, T6- 6 t ha-1 FYM + 20 kg N + 13 kg P, T7- 5 t ha-1 crop residues + 20 kg N + 13 kg P, T8- 6 t ha-1 FYM and T9- 5 t ha-1 crop residues (CR) laid out in a randomized block design (RBD) having three replications. Different K fractions in soil sample viz., water soluble-K, available-K, exchangeable-K, non-exchangeable-K, lattice-K and total-K were determined following standard methods. The mean values were grouped for comparisons and the least significant differences among them were calculated at p<0.05 confidence level using ANOVA statistics. The results of present study revealed that to sustain K status in Vertisol there is a need of K application along with organic manure/crop residue. The application of organics with and without N and P application can sustain the Lattice-K availability in long run under soybean based cropping system of Vertisols. The rate of chemical fertilizer can be reduced up to 50% due to long term application of 6 t ha-1 FYM or 5 t ha-1 crop residues are added to soil.