Evaluating Effects Of Tillage Practices On Soil Organic Carbon Sequestration In Black Soil Based On Least Limiting Water Range

Based on a conservation tillage experiment on a black soil in Dehui, JilinProvince, this study selected soil physical properties, soil organic carbon (SOC)content, specific soil organic carbon mineralization rates (RESPsp), soil CO₂effluxrate and through the process of sensitivity analysis and calibration of least limitingwater range (LLWR) related parametres to analysis soil physical elements that affectthe LLWR in black soil, and then study the impacts of soil physical properties on SOCbased on LLWR. The main results of the research were as follows:(1) By sensitivity analysis, defining LLWR related parameters of black soil, thatis Ψ_fc=0.033MPa,Ψ_wp=1.5MPa,afp=20%,SR=3MPa. It has been obtained theparameter of upper and lower limit and improved calculation method, introducingstratification calculation method.(2)By the correlation analysis between LLWR values and soil physical properties,it has been obtained that soil bulk density, soil penetration resistance and soil porosityespecially small macropores affected LLWR greatly. It has been attempted to usesmall macropores instead of soil bulk density to calculate LLWR and then made acomparative analysis with the LLWR value calculated from soil bulk density.(3)The impact of different tillage practices on soil physical properties isexpressed as follows. No tillage (NT) increased soil bulk density in0-20cm depth.NT increased soil penetration resistance of surface layer and its remarkable effectoccurred in the depth of2.5to17.5cm. Soil penetration resistance was obviously lessafter than before the freezing-thawing cycle (p<0.05). Soil penetration resistancechanges in amplitude before and after freezing-thawing cycle under different tillageand rotation practices with different soil water contents is between47.2%-100.9%,while changes in amplitude in the case of the same water content is between16.1%-44.1%. Compared with Mould plough (MP), NT decreased total soil porosity,resulted in10%to16%increase of large macropores at0-5cm and20-30cm depths,while led to decrease in small macropores in5-20cm layer. The amounts of meso-and micro-pores at different depths under two tillage practices were similar. Differenttillage practices had no significant effects on different size fractions of soil particle(p>0.05).(4)NT significantly increased SOC at the top0-5cm, but showed a reduction at5-30cm depths. NT practices resulted in remarkable SOC stratification ratio to MP. The SOC stocks (0-30cm) were less under NT than under MP for equivalent soilmass based calculation. There was no significant difference in SOC stocks (0-30cm)under two tillage practices using equivalent soil depth method.(5)The soil CO₂flux under different tillage practices showed a significantseasonal variation. SOC RESPsp was lower under NT than MP in the same rotationpractices, while SOC RESPsp in corn-soybean was significantly greater thancontinous corn rotation practices (p<0.05).(6)There was a positive correlation between LLWR and RESPsp or soil CO₂efflux rate. Using small macropores instead of soil bulk density to calculate LLWRcould be more sensitivity to reflect the soil carbon sequestration capacity.(7)Among soil physical factors, bulk density, penetration resistance and porosityhad a greater impact on soil carbon sequestration. Soil bulk density and penetrationresistance increased, small macropores decreased could lead to the reduction ofLLWR. Revised LLWR values can be used to determine which tillage practicesconducive to SOC sequestration more objectively in black soil.