Slow but sure: the potential of slow-release nitrogen fertilizers to increase crop productivity and farm profit in Nepal

Abstract

Reduction of nitrogen (N) input in cropping systems is critical to reduce environmental pollution and achieve sustainable development goals. Multi-location field trials for maize (n = 120) and rice (n = 84) were conducted across nine districts in Nepal during 2018 and 2019 to assess the potential of polymer coated urea (PCU) and urea briquette (UB) to increase agronomic N use efficiency (AEN), crop productivity and farm profits over conventional urea (CU). Nitrogen rates applied in PCU and UB treatments were 22% to 50% lower than CU (120 and 100 kg N ha−1 for maize and rice respectively). In maize, both PCU (8.4 t ha−1) and UB (8.5 t ha−1) applied at 50% and 25% lower N rates respectively produced similar grain yields compared with CU (7.9 t ha−1). Similar results were observed in rice where PCU and UB applied at 22% less N led to a productivity of 5.4 and 5.5 t ha−1 respectively over CU (5.1 t ha−1). Moreover, both PCU and UB increased maize and rice yields significantly compared with current farmer’s practices (FP). In both maize and rice, PCU and UB significantly increased partial factor productivity of N (PFPN) and agronomic NUE (AEN) compared with CU. Furthermore, PCU and UB increased farmer’s net income by US$88 and US$148 in maize and by US$10 and US$87 in rice respectively. These results suggest that PCU and UB could save N input by 22-50% while maintaining similar or even higher yield and higher benefit to farmers compared with CU.