Effects of the Combining Straw Return with Urease Inhibitor on Ammonia Volatilization, Nitrogen Use Efficiency, and Rice Yield in Purple Soil Areas

Abstract

Straw return in rice (Oryza sativa L.) paddy has been heavily criticized for its potential to influence ammonia (NH3) volatilization loss due to irrational fertilizer N application. Therefore, improving the N fertilization strategies within residue straw systems is necessary to reduce N loss from NH3 volatilization. This study investigated how the incorporation of oilseed rape straw and the urease inhibitor affected NH3 volatilization, fertilizer N use efficiency (FNUE), and rice yields over two growing seasons (2018–2019) in the purple soil region. This study arranged eight treatments combined straw (2, 5, 8 ton ha−1, named 2S, 5S, 8S, respectively), with urea or urease inhibitor (UI, 1% NBPT) with three replicates, which included control (CK), UR (Urea, 150 kg N ha−1), UR + 2S, UR + 5S, UR + 8S, UR + 2S + UI, UR + 5S + UI, UR + 8S + UI, based on the randomized complete block method. Our results indicated that incorporating oilseed rape straw increased NH3 losses by 3.2–30.4% in 2018 and 4.3–17.6% in 2019 than the UR treatment, attributing to the higher NH4+-N content and pH value within floodwater. However, the UR + 2S + UI, UR + 5S + UI and UR + 8S + UI treatments reduced NH3 losses by 3.8%, 30.3%, and 8.1% in 2018 and 19.9%, 39.5%, and 35.8% in 2019, separately compared to their corresponding UR plus straw treatments. According to the findings, adding 1% NBPT significantly decreased NH3 losses while incorporating 5 ton ha−1 oilseed rape straw. Furthermore, adding straw, either alone or in conjunction with 1% NBPT, increased rice yield and FNUE by 0.6–18.8% and 0.6–18.8%, respectively. Otherwise, NH3 losses scaled by yield in the UR + 5S + UI treatment decreased significantly between all treatments in 2018 and 2019. These results suggest that optimizing the oilseed rape straw rate combined with 1% NBPT applied with urea efficiently increased rice yield and reduced NH3 emissions in the purple soil region of Sichuan Province, China.