Effects Of Long-term Different Management Practices On Soil Respiration And Soil Organic Carbon

Soil organic carbon(SOC) is a key matter for soil nutrient supply and atmospheric carbon dioxide sequestration. There is a need to better understand soil carbon dynamics and management-induced carbon pool difference. A field experiment was carried out in a non-irrigated winter wheat (Triticum aestivum L.) field with the aim of evaluating the effects of different management practices on soil respiration, soil aggregate stability and soil organic carbon. The five treatments which selected in this study were reduced tillage(RT), No tillage(NT), two crop per year(TC), sub-soiling(SS), and conventional tillage(CT). trenching method was used for soil reparation(Rs) fractionation to study Rs diurnal and seasonal dynamics; dry and wet sieving were used to study soil aggregate stability and relationship to SOC; chemical fractionation methods were used for SOC dynamic study. Such understanding will provide information on how management practices influence SOC dynamics, and therefore, their role to mitigate, or contribute to, the greenhouse effect. fertility. The following results were obtained in this study:Total soil respiration(Rt) varied diurnally with the soil temperature changing. CT and RT had higher Rt at the turning green period of winter wheat growth, and went down rapidly, however the changes of Rt in NT and SS were much moderate. soil water content is a important factor which affects the variation of heterotrophic respiration(Rh)and autotrophic respiration (Ra) in dryland field.An exponential function provided the best fit for describing the relationship between Rs and 5 cm temperature. The Q10 is between 1.24-2.06. The NT treatment had smaller Q10 value, which mean that it is less sensitive to temperature. The NT had lowest Rt and significantly lower than CT to 30.9%, and had the lowest Rh, but the difference is not significant to other treatment. The Rh of NT,TC,SS,CT account to 64%,73%,77%和63% of Rt respectively.Tillage affection to Rt was in short-term, the Rt of RT SS and CT after 1 hour of tillage increased 53%,32%,39% compare to the Rt of before tillage respectively. The differences of Rt disappeared after 40 days of tillage compare to the Rt of before tillage. The NPP of NT and SS increased 5.1和5.2% compare to CT. even the NPP of CT is low during winter wheat growing season, it got extra harvest during summer time compare other treatments.Long term soil management practices affected soil aggregate stability. NT and SS increased the formation of big dry sieving aggregate. at 0-5cm layer, aggregate stability(AS) of NT and SS increase 7.8%和9.3% compare to CT. at 5-20cm, NT and SS had the higher mean weight diameter(MWD) value which are 2.15 and 2.16mm, and TC had the lowest MWD. At the 30-40cm depth, the MWD of NT and CT were similar. For the wet sieving, NT increased the aggregate stability at surface layer (0-5cm)only. TC had higher water sieving aggregate stability even it had lower dry sieving stability compare to other soil management practices. The soybean root or root secretion maybe are useful for the water stable aggregate formation.The mechanisms of dry and wet sieving aggregate stability are not the same. The contents of soil organic carbon (SOC) were negative correlate to dry sieving aggregate stability and positive correlate to wet sieving aggregate stability. For wet sieving, the correlation coefficient is significantly to 0.699.Soil management practices affected soil SOC and total nitrogen content after 10years treatment. For at 0-5cm layer, the SOC of NT is 8%,9%,30.8% and 32.4% higher than SS, CT, CT and RT respectively. The SOC content of NT and SS were higher than CT and RT at soil layer up to 20cm, however the order was reverse when soil depth lower than 20cm.0-40cm soil average SOC content,TC is 17.6% higher than CT, however NT and SS is 0.6%和1.3% lower than CT respectively. At 0-5cm layer, the high active carbon content of SS is highest to 0.58g kg-1. High active, medium active and active carbon account to 4.9-7.3%,18.6-29.4% and 18.6-41.1% of SOC respectively.After 10 years of different Soil management practices, TC had the highest equal depth carbon density and was 12% higher than CT, however, NT and SS were 9% and 6% lower than CT. for the equal mass carbon density, TC was 16.3% higher than CT, NT and SS were 8.1% and 6.3% lower than CT. NT was just change the distribution soil carbon content in soil profile, but did not increase the carbon pool, soybean planting during summer time increased the carbon pool.