Different levels of potassium effect on potassium fractions under soybean grown on farmer’s field in vertisols

The field experiment was conducted to assess the effect of various levels of potassium on its forms under soybean grown on farmer’s field in vertisols at Kanehri, Tq. Barshitakli, Dist. Akola during Kharif 2015-16.The experiment was conducted on farmer’s field comprised four treatments and six replications (one farmer as one replicant) laid out in Randomized Block Design. The treatments comprised of 30:75:00 kg NPK ha-1 (T1), 30:75:30 kg NPK ha-1 (T2), 30:75:60 kg NPK ha-1 (T3) and 30:75:90 kg NPK ha-1 (T4). The results revealed that, increasing levls of K significantly increased all the K fractions. However, highest value of water soluble K (34 mg kg-1), exchangeable K (152 mg kg-1), non-echangeable K (586 mg kg-1), lattice K (10535 mg kg-1) and total K (11305 mg kg-1) were recorded with the application of 30:75:90 kg NPK ha-1. The sequential order of dominance of different fractions of K were lattice K>non-exchangeable K> exchangeable K and water soluble K. The per cent contribution of different fractions of K to total K were followed in the order of lattice K (93.29 %), non-exchangeabl K (5.14 %), exchangeable K (1.32 %), and water soluble K (0.26 %). There exists positive and significant correlation among various K fractions indicating dynamic equilibrium. The contribution of non-exchangeable K to total K uptake was increase with the decrease in the rate of potassium application. The higher contribution of non-exchangeable K to total K uptake (22.39 kg ha-1) was noted with the application of 30:75:00 kg NPK ha-1 followed by application of 30:75:30 kg NPK ha-1. The higher per cent contribution (84.87%) was noted with the lower level of K application. Potassium use efficiency increase with the decrease rate of potassium application. The higher potassium use efficiency (5.24%) was noted with the lower level of K application (30 kg K2O ha-1) followed by application of 30:75:60 kg NPK ha-1 (3.95%).