Effects Of Tillage And Nitrogen Fertilizer Management Practices On Soil Organic Nitrogen Components And NH₃Volatilization From Paddy Field

A field experiment was conducted to investigate effects of tillage and nitrogen management practices on soil organic nitrogen components and NH3volatilization flux from paddy field in a rape-rice crop system in southeast Hubei Province. In the field experiment, there were two tillage measures and five nitrogen managements: conventional tillage (CT) and no-tillage (NT), no fertilization (NO), urea fertilizer (U), long-acting slow-release compound fertilizer (SR), urea fertilizer+half amount of organic fertilizer (U+MO) and urea fertilizer+total amount of organic fertilizer (U+TO). The purpose of this study was to provide scientific basis for conducting fertilizing, improving nitrogen utilization efficiency of rice and reducing environmental pollution. The main results were as follows:1. Compared with CT, NT significantly increased the content of HUN in soil by9.1%(P<0.05). Compared with NT, CT significantly increased the content of ASN in soil by10.1%(P<0.05).Compared with other fertilization treatments, SR significantly increased the content of HUN in0-5cm soil by16.9%-69.4%(P<0.05), and U+MO significantly reduced the content of AN in0-5cm soil by4.2%-9.9%. Compared with U and SR, U+MO contributed more to the contents of AAN and THAN in soil by1.9%-39.9%and8.5%-32.2%, respectively (P<0.05).2. The cumulative NH3emission flux loss of NT was7.3%higher than that of CT (P<0.05).NH3emission flux was a major way of nitrogen loss in paddy fields; SR and U+MO significantly reduced the cumulative NH3volatilization flux loss. Compared with other fertilization treatments, the cumulative NH3emission flux loss of SR reduced by18.7%-36.2%(P<0.05), and NH3volatilization flux loss rate of SR significantly reduced by38.0%-61.2%(P<0.05). Compared with U and U+TO, the cumulative of NH3emission flux loss of U+MO reduced by10.1%-21.5%(P<0.05), and NH3volatilization flux loss rate reduced by17.2%-32.2%(P<0.05).3. There were significantly positive correlations between the cumulative of NH3volatilization flux loss and the contents of organic nitrogen in soil:THAN, AAN, NHN and SON (P<0.05), and significantly negative correlation between NH3volatilization flux loss and the content of HUN in soil (P<0.05), and significant correlation between the cumulative of NH3volatilization flux loss and soil urease activity (P<0.05). Significantly positive correlation was also discovered between NH3emission flux and the characteristics in paddy:soil NH4+, soil pH, floodwater NH4+, floodwater NO3-and pH (P<0.05).4. Tillage had no significant effect on rice yields. Compared with NT, CT increased the nitrogen utilization efficiency by5.6%(P<0.05). Compared with other fertilization treatments, U+MO significantly increased rice yields by11.0%-23.4%(P<0.05). There were no significant differences in rice yields between SR and U. Compared with other fertilization treatments, U+MO increased the nitrogen utilization efficiency, nitrogen partial factor productivity and agronomic efficiency of nitrogen by26.1%-46.6%(P<0.05),14.4%-31.0%(P<0.05) and17.5%-113.7%(P<0.05). But there were no significant differences in nitrogen utilization efficiency between U and SR.Above all, we concluded that CT-SR increased the content of organic nitrogen, particularly the soil HUN content, and CT-SR significantly reduced NH3volatilization flux. Moreover, CT-SR had stable rice yields. CT-U+MO increased the content of some organic nitrogen component, and CT-U+MO significantly reduced NH3volatilization flux and increased nitrogen utilization efficiency. Moreover, CT-U+MO largely increased the rice yields.