Effect Of Maize Stalk Retention On Nitrous Oxide Emission And Ammonia Volatilization In Arable Brown Soil

Nitrogen (N) is one of the necessary nutrient elements for crop growth, and plays a vital role in improving crop yields. However, excessive use of N fertilizers leads to air pollution, greenhouse effect, eutrophication and a series of ecological and environmental problems. Stalk was recognized as a cheap and available biological resource containing N, phosphorus, potassium and other nutrients. With the development of agricultural managements, the returning of stalk to field has attracted increasing attention. No tillage and stalk mulching could change micro-environment of soil surface. The significant changes in soil N mineralization/immobilization process affect the dynamics of soil inorganic N and soil N cycle in some extent, while the impact of stalk mulching on gaseous N losses in arable soil remains uncertain currently. To explore the effect of stalk returning on N gas loss in no tillage field, this study set up a 15N tracing microplot experiment and monitored ammonia (NH3) volatilization and nitrous oxide (N2O) emission dynamics in brown soil in situ. Aeration method and closed static chamber measurement were chosen to study NH3 volatilization and the release of N2O, respectively. The content of inorganic N in soil was also determined after fertilization. The 15N enrichment in NH3 and N2O was measured with isotope ration mass spectrometry (IRMS) and gas chromatography (GC) to differentiate the origins of N in the released NH3 and N2O.We found that the plots with 50% stalk returning produeced the maximum loss of NH3 during observation period, while 100% treatment insignificantly decreased N loss compared to N fertilization only. The NH3 volatilization loss rate (the loss per unit input N) in 100% stalk returning was significantly lower than those in N fertilizer application only and 50% stalk returning plots after a growing season (4.6% vs. 6.1%.) The NH3 volatilization losses accounted for 4.2-4.3% and 1.9% of fertilizer N and stalk N, respectively, at both 50% and 100% maize stalk returning treatments. The N2O emissions from the arable soil were higher in stalk mulching plots (1.5-1.6 kg hm-2) than those in N fertilizer applied plots (1.4 kg hm-2). The losses of N2O increased with the increasing amount of returned stalk application. However, the N loss rates (per unit fertilizer N) were significantly lower in stalk returning plots than those in N fertilizer applied plots, with the magnitude of 0.62% and 0.72%, respectively. The fertilizer-derived N2O losses were 0.7-0.8% of the N application and the stalk-derived N2O losses were 0.02% of the stalk N. The enhanced crop N-requirement at silking stage than other periods contributed to the reduced NH3 volatilization and the accumulation of N2O. We conclude that no-tillage with stalk returning has no significant impact on N2O emission in the arable soil. Stalk returning at the whole yield can reduce NH3 volatilization and N2O emission as well as the decrease of N gaseous loss rates. It was thus suggested that 100% stalk returning as an effective management to reduce N loss accordingly. And for improving N utilization efficiency of maize, we also suggest applying more N fertilizer at silking stage.