| Citrus(Citrus reticulata Blanco)is one of the important economic forests compatible with economic and ecological benefits in southern China.Red soil in southern China has the characteristics of strong carbon sink capacity and high carbon sequestration potential under scientific,reasonable and effective carbon sequestration measures,which plays an important role in the realization of carbon peak and carbon neutrality.At present,there are few studies on the selective migration of soil organic carbon in citrus orchards under natural rainfall conditions.The mechanism of selective migration of soil organic carbon is not clear,and the variation law of soil annual erosion is not clear.Therefore,in this study,citrus + straw mulching(CS)was used as the research object of non-biological mulching measures;citrus + radish peanut rotation(CRP)as the research object of tillage measures;citrus + clover cover(CC),citrus + clover strip cover(CCS),and citrus + moss cover(CT)were the research objects of biological measures;citrus + bare land(CB)was selected as the control study object,and the effects of different management measures on the selective migration of soil organic carbon in citrus orchards on red soil slopes were studied.The aim was to clarify the response law and mechanism of soil organic carbon selective migration and sediment organic carbon enrichment ratio to citrus orchards on red soil slopes under different management measures,clarify the interannual variation of soil carbon under annual erosion rainfall conditions,enrich the research on soil erosion law of newly developed orchards on red soil slopes,deepen the scientific understanding of the relationship between soil erosion and carbon cycle,and have important theoretical and practical significance for controlling soil erosion and soil organic carbon loss from the source.The main research results are as follows :(1)The annual erosive rainfall in the study area is mainly long-duration moderate rainfall,which is concentrated in March – September.The prevention and control of soil erosion should focus on May and September.The flow reduction benefits of different management measures were CC > CCS > CS > CT > CRP.There was a significant positive correlation between sediment yield and runoff under different management measures.The effect of sediment reduction under different management measures was as follows : complete coverage > strip coverage > straw coverage > radish peanut rotation > moss coverage.(2)The concentrations of dissolved organic carbon(DOC)in runoff soil of six different management measures were as follows : clover strip cover CC > straw cover CS > bare land CB > moss cover CT > clover strip cover CCS > radish peanut rotation CRP and organic carbon concentration were negatively correlated with rainfall intensity.The total loss of soil DOC was as follows : clover strip cover CCS > straw cover CS >radish peanut rotation CRP > clover strip cover CC > bare land CB > moss cover CT.Under different rainfall patterns,the response of different measures is different,mainly for moderate rain : soil DOC loss of clover and rice straw management measures is larger;under heavy rain conditions,the management measures of clover could significantly increase the soil DOC loss,and there was no significant difference in the management measures under heavy rain conditions.(3)The amount of sediment organic carbon loss of different management measures is : bare land CB > clover cover CC > radish peanut rotation CRP > moss cover CT >clover cover CCS > rice straw cover CS;runoff,rainfall intensity and rainfall were negatively correlated with sediment organic carbon content.Under moderate and heavy rainfall conditions,there were significant differences in organic carbon of sediment between straw mulching CS,clover strip mulching CCS and bare CB(P0.05).There was no significant difference under rainstorm conditions.(4)The enrichment ratio of organic carbon in runoff plots under different management measures was straw mulching CS > radish peanut rotation CRP > moss mulching CT >bare land CB > clover mulching CC > clover strip mulching CCS;under moderate and heavy rain conditions,there were significant differences in the aboriginality between CS,CS and CB(P>0.05).(5)Under moderate rainfall conditions,the proportion of runoff migration organic carbon in runoff plots with different management measures was greater than that of sediment migration organic carbon.The proportion of runoff migration was between 0.4and 0.8 and the size was : clover strip covered CCS > rice straw covered CS > clover covered CC > radish peanut rotation CRP > moss covered CT > bare CB.Under heavy rain conditions,the proportion of organic carbon migration in runoff of management measures was 0.06 – 0.53,and the order was as follows : Stripe grass cover CCS >straw cover CS > radish peanut rotation CRP > Stripe grass cover CC > moss cover CT > bare land CB.Under heavy rain conditions,the proportion of runoff loss in runoff plots of different management measures was 0.07 – 0.34,and the sizes were as follows :Stripe grass cover CCS > radish peanut rotation CRP > straw cover CS > Stripe grass cover CC > moss cover CT > bare land CB.The total amount of soil organic carbon migration decreased by 273 %(CS),121 %(CRP),344 %(CCS),337 %(CC)and110 %(CT),respectively,compared with bare land CB.(6)The content of soil total organic carbon(TOC)decreased under different management measures,such as straw cover CS,radish peanut rotation CRP,clover strip cover CCS,clover cover CC,moss cover CT soil TOC decreased by 58.82 %,95.47 %,75.08 %,78.24 %,44.13 % respectively compared with bare CB.The soil carbon storage decreased with different management measures of 0 – 100 cm,and the 1 m carbon erosion amount of bare CB soil reached 12.66 t / hm2.Compared with bare CB,the carbon loss was inhibited by 32.31 %,85.98 %,62.60 %,62.89 % and 48.15 % in straw mulching CS,radish peanut rotation CRP,clover strip mulching CCS,clover whole mulching CC and moss mulching CT,respectively.(7)Soil DOC content of different management measures increased,and annual rainfall erosion had a greater impact on 0-10 cm soil.In the soil of 10 – 20 cm,the interannual difference of DOC content in different management measures was eliminated,and the increase effect of straw mulching and moss mulching on DOC in the soil of 20 – 40 cm was not obvious.Soil microbial biomass carbon(MBC)decreased among different management measures.The effect of rainfall on soil MBC was limited to 0-20 cm,while the effect on 20-40 cm was limited.In summary,different management measures in citrus orchards on red soil slopes in southern China can reduce soil runoff,sediment yield,and sediment organic carbon loss,and increase DOC loss in runoff.In the interannual variation,the DOC content in different soil layers increased,and the soil organic carbon content,soil carbon pool storage and soil microbial biomass carbon decreased.The form of soil organic carbon loss is mainly runoff loss under moderate rain conditions,and the proportion of runoff and sediment loss is roughly the same under heavy rain conditions,and sediment loss is mainly used under heavy rain conditions.In terms of the comprehensive effects of various measures on carbon sequestration and sink enhancement and the targeted management measures to reduce the loss of organic carbon in orchards on red soil slopes,three measures,namely,whole-shrub coating,strip coating and straw coating,are worth promoting. |
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