Study On Carbon Decomposition And Residue In Soil Aggregates Of Newly Added Straw Under Plastic Film Mulching And Fertilization

Straw returning is an important technical measure to increase soil organic carbon storage.Aggregates,as the fundamental unit of soil structure,are the main places for straw carbon and other exogenous carbon to be immobilized in soil.The turnover of straw carbon in the soil mainly depends on the role of soil microorganisms.At present,there are many researches on the fixed transfer of straw carbon in farmland soil aggregates.However,the decomposition of straw carbon under plastic film mulching?"mulching"?and different fertilization,microbial utilization of straw carbon?C?and residual C in soil aggregates have little known.Based on the Long-term Experiment Station of Brown Earth in Shenyang Agricultural University,the ¹³C-labeled maize straw was added to soils,and then the content of organic C in soil and aggregates and the microbial biomass C derived from straw C were determined.The decomposition of C and its residue in soil aggregates under mulching and fertilization were discussed.Four fertilization treatments were chosen,including no fertilization?CK?,single application of nitrogen fertilizer?N2?,single application of organic manure?M2?and organic manure combined with nitrogen fertilizer?M1N1?treatment,under no-mulching and mulching.The main results were shown as follows:?1?The soil organic carbon?SOC?content under mulching treatments was lower than the corresponding fertilization treatment under no-mulching,indicating that the mulching could accelerate SOC decomposition.After the straw was added to soil for180 days,the ¹³C-SOC content in CK,N2,M2 and M1N1was0.35 g kg^-1,033 g kg^-1,0.31g kg^-11 and 0.30 g kg^-1,respectively,under mulching and it was 0.32 g kg^-1,0.29 g kg^-1,0.30 g kg^-1,and 0.29 g kg^-1,respectively,under no-mulching.The content of straw C(¹³C-SOC)in SOC decreased with the incubation time in no-mulching and mulching.During the cultivation period,the residual rate of straw under mulching soil was lower than that of no-mulching soil.The residue rate of C in CK was the highest,the average of no-mulching and mulching was 53.25%and 48.02%,and the average of no-mulching and mulching in the M1N1 treatment was 33.99%and 28.95%respectively.?2?Straw increased soil microbial biomass carbon?MBC?content,but MBC content decreased with the extension of incubation time.M2 and M1N1 treatments significantly?P<0.05?increased soil MBC content.Mulching had higher soil MBC content than no-mulching in the same treatment.The content of MBC derived from straw C(¹³C-MBC)in the treatment ofM2 treatment had the highest content of¹³C-MBC under the same mulching conditions,with an average of 71.09 mg kg^-1;M1N1 was the highest under the same no-mulching,with an average of 57.60 mg kg^-1.Whatever with or without mulching,the CK treatment had the lowest content of¹³C-MBC,which ranged from 29.88 mg kg^-11 to 41.56 mg kg^-1.After 180 days of straw addition,the contents of ¹³C-MBC in M2 and M1N1 treatments were significantly?P<0.05?higher than those in N2 and CK treatments.?3?The carbon content of residual C in different mulching and fertilization soils was first enriched in 0.25¹mm size aggregates,and it accounted for 3.64%⁹.45%of aggregate organic carbon,respectively.On the other hand,the carbon content of residual C was lower in>2 mm and 1² mm size aggregates,accounting for1.60%³.03%.With the increase of culture time,the content of residual C in 0.25¹mm and<0.25 mm size aggregates was decreased,while the content of residual C in>2mm and 1² mm size aggregates was increased,indicating that small aggregates facilitated the decomposition of external carbon.The content of residual C under mulching in<0.25 mm size aggregates were higher in M2 and M1N1 treatments and in0.25¹ mm size aggregates were the highest in CK treatment,and in 1² mm size aggregates were the highest in N2 treatment.Compared with no-mulching soil,mulching decreased straw carbon content in soil aggregates.?4?The mulching and fertilization caused C storage in agglomerates to gradually transfer to large aggregates over time.0.25¹ mm size aggregates had the highest C storage and were the main grain size of storage C,and in 1² mm size aggregates were the lowest.The C storage in 0.25¹ mm size aggregates under plastic mulching were significantly?P<0.05?higher than that in no-mulching soil under N2 treatment.C reserves in>2 mm size aggregates were the highest in M1N1 treatment.C reserves in1² mm size aggregates were the highest in N2 treatment,and the percentage of aggregate was the largest.C reserves in 0.25¹ mm and<0.25 mm size aggregates were the highest in CK treatment.All the results showed that the content of soil straw carbon in 0.25¹ mm size aggregates were high,which were the highest straw carbon reserve of aggregates,and it has a strong ability to enrich and protect the straw carbon.Film mulching and fertilization can promote the decomposition of straw carbon in soil by affect the activity and species of soil microorganisms,and reduce the residue of straw carbon in soil.Therefore,plastic film mulching and organic manure were effective measures to promote the decomposition of straw and ensure the sustainable utilization of soil.