Chemical fractionation and bioavailability of potassium as affected by digestate in a degraded Ultisol under maize cultivation

ABSTRACT Application of soil amendment enhances redistribution of potassium (K) forms which affects K availability. Information on the effect of soil amendment on soil K dynamics is vital for management of soil K. The effects of digestate on dynamics of water soluble (WS), exchangeable K (Exch), non-exchangeable (Non-Ex) and mineral (Min) K fractions as well as maize growth and potassium uptake were investigated under a factorial experiment arranged in a completely randomized design of 5 (0, 5, 10, 15, 20 t ha−1 digestate) × 3 (2, 4, 6 weeks after planting (WAP) ×2 (two growth cycles of maize). During incubation experiment, digestate application increased K fractions and altered the order of distribution of K fractions from Min > Exch > non-Ex > WS in the control soil to Min > WS > Non-Ex > Exch in the amended soil. Potassium availability increased with WAP in first cycle but decreased with WAP in second cycle due to crop uptake. Potassium uptake and dry matter yield were better in first cycle relative to second cycle. Complementing digestate with mineral fertilizer would improve K uptake and maize growth.