Effects of soil straw return and nitrogen on spring maize yield, greenhouse gas emission and soil enzyme activity in black soils

Northeast China spring maize production area is among the main maize cultivation regions in China. Due to located in high latitude region and singling cropping system, spring maize fields in black soil region of Northeast China is less reported as for researches on farmland greenhouse effects. It is therefore important to explore the effects of straw return to soil and nitrogen application on maize grain yield and greenhouse gas emissions in the area. In this study, a two-factor straw return (no straw return and straw return) and three-factor nitrogen (N) application (N: 120 kg·hm^-2, 240 kg·hm^-2 and 300 kg·hm^-2) field experiment was conducted in a randomized block design. Total emissions of CO₂, N₂O and CH₄, global warming potential of CO₂-eq and greenhouse gas emissions intensity (GHGI), soil catalase and urease activities were determined in the experiment. The results showed that the highest yield was observed in straw return with medium N dose (240 kg·hm^-2) treatment, which was not significantly different from that of the highest N dose (300 kg·hm^-2) with no straw return treatment (P > 0.05). With increasing N dose, CO₂, N₂O and CH4 emissions, global warming potential of CO₂-eq, and GHGI significantly increased under no straw return conditions. On the other hand, N application with straw return only enhanced CO₂ and N₂O emissions, while soil CH4 carbon sink increased (P < 0.05), and greenhouse gas emissions and intensities (CO₂-eq and GHGI) did not increase remarkably (P > 0.05). Under no straw return conditions, N application reduced soil catalase activity and enhanced soil urease activity with increasing N application. However, straw return improved the decreasing range of soil catalase activity, and weakened the increasing range in soil urease activity caused by increased N application. Therefore, straw return with N application enhanced grain yield, with the highest yield under medium N application treatment (N: 240 kg·hm^-2). Medium N application with straw return limited greenhouse effects compared with no straw return in the experiment. The results were valuable for the recommendation of N application rates in spring maize cultivation in black soil regions.