Nitrate Released And Nitrous Oxide Emission Under Different Soil Pore Characteristics

Soil pore structure is vital for air and water transports,and is highly variable under different fertilization practices.Soil tillage or compaction is known to alter air and water conditions within soils,then contributed to some environmental consequences,like N₂O emission and nitrate excessive leaching.In microscale soil cores,pore connectivity and pore size distribution play an important role in these nitrogen transformation processes.In this study,three physical disturbance treatments:intact（Intact）,sieved by a 5mm mesh and repacked（Sieved）,and compacted（Compacted）were measured on three fertilization soils（no fertilizer（Control）,inorganic fertilizer（NPK）,and organic fertilizer（OM））to simulate different soil pore structure.Results reveal that:1)The OM fertilization presented a significantly higher macroporosity of pore size>1000μm,while NPK fertilization had a higherΧνthan the Control.The Compacted treatment significantly decreased macroporosity,mean diameter（MD）,connectivity（Γ）,specific Euler number（Χν）,compactness（CP）and macoporosity of the limiting layer（MPLL）,and the Sieved treatment significantly reduced>1000μm macroporosity compared with the Intact treatment.2)N₂O emission was highly related to water-filled porosity and soil organic carbon content.The Sieved and Compacted treatments increased N₂O emission in the OM fertilization treatment.The rate of N₂O emission was related to soil p H and soil organic carbon content.3)Long-term NPK fertilization decreased soil microbial biomass C and N,but increased the abundance of AOA.Long-term OM fertilization increased the abundance of AOB.In the NPK and OM fertilization treatment,the Compacted treatment decreased the NO₃^-release from soil or urea.In the NPK treatment,the Sieved treatment increased the NO₃^-release from soil;in the Control treatment,the Sieved treatment increased the NO₃^-release from urea.The porosity with diameter of 100-500μm,pore connectivity and air permeability were related to the NO₃^-release potential and rate.The soil organic carbon content was negative related to the NO₃^-release potential.The soil organic carbon content and macropore characteristics determined the NO₃^-release potential from urea.