Optimizing polyhalite (POLY-4) use in the maize-wheat system: A comparative case study from upper and Trans Indo-Gangetic plains of India

Increasing complexity in crop nutrient requirement in intensive crop production systems needs alternate multi-nutrient sources. Polyhalite (POLY-4) which contains 14% K2O along withcalcium (17% CaO), magnesium (6% MgO), and sulfur (19% S) can be a possible recourse in this regard. In maize-wheat systems, it was evaluated for productivity, profitability, nutrient usage, and nutrient use efficiency under Indo-Gangetic plain (IGP) zones for consecutive two years (2018-19 and 2019-20). The results revealed that 150% K through POLY-4 produced the maximum maize grain yield under the Trans Indo-Gangetic plains (TGP). The maize grain yield increased by 20.8% and 26.2% under 100% K (POLY-4) and 150% K (POLY-4) over No-K, respectively. But statistically, 100% K (POLY-4) stands similar with both 150% K (POLY-4) and 150% K through muriate of potash (MOP) and equivalent. The trends were noticed under upper Indo-Gangetic plain zones (UGP) also. Similarly, the maximum wheat grain yield (6.12 and 6.29 t/ha under TGP and UGP, respectively) was obtained under 150% K (POLY-4), and remained statistically at par with 100% K (POLY-4), but significantly higher than 150% K (MOP). Under both agro-ecologies i.e. TGP and UGP, the highest system productivity was obtained with recommended N, P, and 150% K application through POLY-4. The added return over NPK remained highest with 150% K (POLY-4) for both maize and wheat. However, higher partial factor productivity for N and S, agronomic, physiological, and translocation efficiencies were noticed under 150% K (POLY-4), and remained at par with 100% K (POLY-4). Increased system yield, added returns, partial factor productivity, agronomic, physiological, and translocation efficiencies under 100% K through POLY-4 (along with recommended N and P) proved its effectiveness as multi-nutrient source for the maize-wheat system under TGP and UGP.