Nitrous oxide emissions and maize yield as influenced by nitrogen fertilization and tillage operations in upland soil

Previous studies simply focused on determining nitrous oxide (N2O) emissions from the soil under different tillage operations and nitrogen (N) fertilizations without considering crop yield. Therefore, the objective of this study was to determine the effects of different tillage operations and N fertilizations on N2O emissions and crop yield from upland soil. Two different tillage operations [conventional tillage (CT) and no-tillage (NT)] and N fertilizations [without urea (WOU) and with 186 kg N ha−1 of urea (WU)] were established in a randomized block design with three replications on upland soil. Maize (Zea mays) was cultivated from 6th July to 4th October, 2018 (year 1), and from 15th April to 26th July, 2019 (year 2). The daily N2O flux did not peak soon after tillage operation and N fertilization, but it was more related to the change in water-filled pore space (WFPS). The mean value of WFPS across N fertilizations and seasons (years) was higher in CT than in NT. The changes of nitrification and denitrification rates could be attributed to the differences in WFPS between CT and NT. Nitrification was the predominant process producing N2O with CT, but denitrification was with NT. The application of urea increased cumulative N2O emissions, while CT also increased it compared with NT. The order of the mean values of cumulative N2O emissions across seasons from the highest to the lowest was as follows: CT + WU (7.12 kg N2O ha−1 year−1) > NT + WU (5.69 kg N2O ha−1 year−1) ≥ CT + WOU (5.02 kg N2O ha−1 year−1) > NT + WOU (4.24 kg N2O ha−1 year−1). Tillage operation did not affect the grain yield of maize or yield-scaled N2O emissions (YSNE). However, the application of urea increased the grain yield of maize and decreased YSNE, implying it could reduce N2O emission per unit of maize grain production. No-tillage management did not decrease YSNE value compared to CT operation, but N fertilization significantly decreased YSNE in the current study.