Effect Of Soil Organic Carbon Pool Based On Water Conservation Technology For Dryland Wheat Field

As a part of anthropogenic soil management practices,tillage usually affects soil organic carbon(SOC)turnover and therefore SOC sequestration by changing soil physical,chemical and biological characteristics,which exerts feedback to climate change.This study focused on analyzing the distribution of SOC and its fractions in dryland winter wheat fields under different tillage practices during summer fallow season.Meanwhile,combining with soil physical and aggregate properties,as well as SOC mineralization characteristics,the effects and mechanism of tillage practices during summer fallow season of dryland wheat field on SOC pool were clarified.The experiment was set up including three treatments: no tillage during summer fallow season(FNT),deep plow during summer fallow season(FPT)and subsoiling during summer fallow season(FST),and the main results are as follows:(1)In 2016-2018,compared with FNT treatment,FPT and FST could significantly increase soil water storage before sowing at 0-200 cm soil depth,and the effect could be extended to the period of joiinting or anthesis stage of dryland winter wheat,significantly improved drymattter amount,significantly increased tiller numbers,eventually significantly increasing wheat yield by 14.46%-26.38%,and significantly improving water use efficiency by 10.13%-13.18%.(2)In 2018-2019 and 2019-2020,compared with FST and FPT treatments,FNT significantly increased the concentration of SOC fractions(except HFOC)at 0-10 cm soil depth,and the SOC concentrations within aggregates of each particulate size were highest under FNT treatment.Specifically,FNT treatment significantly increased concentration of SOC fractions by 35.89%-140.96% and 29.19%-132.65% than FST and FPT,respectively.For SOC concentration within aggregates,FNT treatment significantly increased by 2.50%-110.55% and 2.43%-43.37%,compared with FST and FPT,respectively.However,below 20 cm soil depth,the SOC fractions concentration under FPT was higher or significantly higher than those under FST treatment.At 40-50 cm soil depth,POx C,POC and HFOC concentrations were also higher or significanltly higher than those under FNT treatment.In addition,the significantly highest SOC concentrations within aggregrates at 20-40 cm soil depths in 2018-2019 and 2019-2020 were observed under FNT and FPT treatment,respectively.(3)In 2018-2019,FNT treatment significantly increased SOC concentration at 0-50 cm soil depths by 74.03%-172.05% than FST treatment,also increased by 37.96%-58.37% than FPT at 0-10 cm and 20-30 cm depth.In 2019-2020,FNT and FST significantly increased SOC concentration at 0-10 cm by 28.87% and 17.17% than FNT,respectively.However,the SOC concentration at 20-50 cm soil depths all showed as FPT>FST>FNT,and signifcant difference were onserved among three treatments.The stratification rate of SOC decreased gradually with tillage intensity increasing during summer fallow period,especially in 2019-2020.(4)In the 0-50 cm soil profile,with increasing of soil depth,the amount of SOC sequestration under FNT treatment gradually decreased,while decreased firstly and increased then under FST and FPT treatment.At 0-20 cm soil depths,the amount of SOC sequestration under FNT was higher than FST and FPT,while showed as FPT>FST>FNT at 20-50 cm depths.In 2018-2019,compared with FST and FPT,FNT significantly increased the SOC stock of each profile in 0-50 cm by 108%-129% and 31%-85%,respectively.In 2019-2020,in 0-10 cm and 0-20 cm profiles,FNT and FST treatments significantly improved by 14.79%-27.24% and 11.48%-16.03%,respectively,compared with FPT treatment.When the soil profile increased to 0-50 cm,the SOC stock under FPT treatment were significantly higher by 9.21% than that under FNT treatment.No significant difference was observed among three tillage tratment in SOC stock at other soil depths.(5)Different tillage practices changed concentration of SOC and its fractions and the SOC concentration within aggregates of different particle sizes by affecting the physical properties of soil and the distribution of aggregates.The three tillage treatments all increased POx C content by increasing the proportion of mineral-associated and light fraction soil.Meanwhile,the percentage of mechanically stable aggregates within 0.25-2 mm size under the three tillage treatments all showed a significant positive linear correlation with POx C or POC concentration.Furthermore,FST and FPT treatments also increased POC concentration by increasing soil porosity.For the SOC concentrations within aggregates,the proportion of light fraction soil under FNT treatment showed a positive logarithmic correlation with them.Soil porosity under FST treatment showed a significant positive linear correlation with SOC concentration within less than 0.053 mm aggregate.FPT treatment improved the SOC concentration within less than 0.5 mm aggregate by increasing mean weight diameter(MWD)of water-stable aggregates.Similarly,SOC concentration was significantly or extremely significantly positively correlated with the its fraction and aggregate-associated SOC of different size.However,the contribution of SOC fractions to SOC varied under different tillage practices.Specifically,concentration of POC,MOC,HFOC,LFOC and SOC of aggregate less than 0.053 mm all showed significant or extremely significant linear correlation with SOC concentration under FNT treatment.Only MOC,HFOC cocentration showed significant linear correlation with SOC concnentraiton under FST treament.What’s more,concentration of LFOC and SOC of aggregate less than 0.053 mm showed significant linear correlation with SOC concentration under FPT treatment.(6)The incubation experiments results showed that,FPT and FST treatments significantly increased the SOC mineralization rate of 0-30 cm and 30-50 cm soil depths,respectively,and therefore significantly increased the cumulative SOC mineralization amount of the corresponding soil depths by 8.97%-178.68% and 7.10%-106.47%.Compared with FNT and FST treatment,FPT significantly increased the potential mineralizable active carbon pool(Ca)of 0-10 cm soil depth by 32.32%-36.16% and 62.11%-69.88%,respectively,and significantly increased the potential mineralizable inert SOC pool(C_S)of 0-30 cm soil depth by 38.43%-100.08% and 66.40%-302.06%,respectively.Compared with FNT and FPT treatment,FST significantly increased C_S at 40-50 cm soil depth by 62.39%-114.07% and 46.00%-82.55%,respectively.In conclusion,implenting FPT and FST in humid-year and dry-year was beneficial to achieving high yield of dryland wheat,respectively,in Wenxi County,Shanxi Province.In the 0-50 cm soil profile,FPT and FST both showed significant SOC sequestration advantage than FNT in the short tillage period,but the potential mineralization was significantly higher than FNT.Therefore,the combination of FNT with FPT and FST is conducive to the simultaneous realization of wheat yield increase and SOC sequestration in dryland wheat field.