Influence of NPK levels on forms of potassium under foxtail millet (Setaria italica L.) grown in low fertile Alfisol

A field experiment was conducted at Zonal Agricultural and Horticultural Research Station (ZAHRS), Shivamogga, Karnataka during the Kharif seasons of 2017 and 2018 to study the interaction effect of NPK levels on potassium forms and their distribution in soil under foxtail millet (Setaria italica L.) grown in marginal Alfisol. Eighteen treatment combinations were tried in factorial randomized block design which comprises three levels of nitrogen (0, 15 and 30 kg N ha-1), two levels of phosphorus (0 and 15 kg P2O5 ha-1) and three levels of potassium (0, 10 and 20 kg K2O ha-1). The results indicated that the readily available K fractions of soil depleted due to higher levels of NPK and in turn it replenishes from nonexchangeable-K fraction. The lattice-K was not much affected by N, P and K levels but a slight build-up of lattice-K was reported at 20 kg K2O ha-1 during 2018 (652.2 mg kg-1) as compared to initial year (2017 - 647.0 mg kg-1). The individual levels viz., N30, N15, K10 and P15 did not influence positively and significantly reduced all K fractions during 2017 and 2018. The per cent change in available K2O status inferred that higher requirement of potash to foxtail millet which had significantly positive response in plant systems due to increased N levels but remarkable negative balance in soil. The available potassium gets depleted in the soil up to 50% of its initial content during study of two successive cropping seasons and showed remarkable negative balance in various treatment combinations. The soils of marginal Alfisol lacking in good soil texture and K-bearing clay minerals at lower soil pH with low buffering capacity which were fails to supply the available potassium immediately.