Soil Organic Carbon Sequestration Mechanism And Carbon Balance In Dry Farming Red Soil Under Long-Term Different Fertilization

Fertilization is an important measure to maintain soil productivity,and also had a profound impact on the decomposition and transformation of soil organic carbon(SOC).To exploring the process and mechanism of different fertilization measures affects SOC composition,sequestration and turnover were important for improving SOC content,and increasing soil productivity and rational fertilization.Based on two long-term experiments(different fertilization model experiments lasting 29 years and different organic manure application experiments lasting 11 years),this paper systematically expounds the evolution of SOC,difference of SOC components,characteristics of SOC sequestration and its related greenhouse gas emissions(CO₂,CH₄ and N₂O)in red soil under long-term different chemical fertilizer,straw returning,organic manure and organic manure combin with chemical fertilizer.And also,their effects on global net greenhouse potential(NGWP)and greenhouse gas emission intensity(GHGI)of crop production system were evalued.The results showed that average annual increased rate of SOC content after 29 years(1991-2019)were followed by 1.5NPKM 0.34g kg^-1,M 0.28 g kg^-1 and NPKM 0.25 g kg^-1,higher than that CK0(0.22 g kg^-1),NPK(0.13 g kg^-1),and NPKS(0.12 g kg^-1).Annual increased rate of SOC content was NPKM3(0.28 g kg^-1),NPKM2(0.24 g kg^-1),NPKM1(0.20 g kg^-1)and NPK(0.17 g kg^-1),respectivelyafter 11 years(2009-2019)fertilization.The average annual increased rate of SOC_stock in red soil wasfollowed by NPKM 1.02 t hm^-2,M 0.97 t hm^-2 and NPKM 0.81 t hm^-2,CK0 0.77 t hm^-2,NPKS 0.29 t hm^-2,NPK 0.25 t hm^-2,and NP 0.23 t hm^-2.The average annual growth rate of SOC_stock in red soil with long-term different amount of organic manure was NPKM3(0.83 t hm^-2),NPKM2(0.71 t hm^-2),NPKM1(0.50 t hm^-2)and NPK(0.41 t hm^-2),respectively.The effect of organic manureon increasing SOC is better than that of chemical fertilizer,and with the increase of organic fertilizer,the rate of increasing SOC increases.The application of organic manure or chemical fertilizer combined with organic manureis an important measure to increase SOC in red soil.The results of long-term experiments show that SOC level determines the high and stable yield of crops.SOC content directly affects soil carbon,nitrogen pool and crop yield.SOC also indirectly affects crop yield through soil carbon and nitrogen pools.The study on the effect of different fertilization on SOC components of red soil shows that the SOC content of particles and aggregates at all levels in red soil is significantly higher than that of straw and NPK.Compared with the initial stage of the experiment,among the easily decomposable carbon components in the application of organic fertilizer,the organic carbon of sand(SC),coarse sand(CS)and fine clay(FC)increased by 47.9-92.4%,and that of aggregates(cfpoc,ffpoc and ipoc)increased by 191.9-234.6%.The content of easily decomposed carbon and aggregate in NPKs increased by 29.4%and 32.7%,respectively.The content of easily decomposable carbon and aggregate increased 42.5%and 42.9%respectively.The content of easily decomposable carbon and aggregate decreased by 21.1%and 7.6%respectively.The effect of long-term application of organic manureon carbon accumulation of particles and aggregates was significantly higher than that of other treatments.Compared with other treatments,organic manureapplication mainly increased soil aggregate socstock.For the chemical stability SOC of red soil,the average annual growth rate of the content of active organic carbon(LOC)in red soil with long-term application of organic manureand chemical fertilizer organic manure(M,NPKM and 1.5NPKM)was 0.17-0.21g kg^-1,0.12 g kg^-1,0.08 g kg^-1 and 0.05 g kg^-1 respectively,which was higher than that of NPKs,NPK and CK.For microbial utilization of SOC in red soil,the microbial biomass carbon(MBC)content of long-term application of organic manureand chemical fertilizer organic manure(M,NPKM,1.5NPKM)was significantly higher than that of chemical fertilizer combined with straw return(NPKS),significantly higher than that of chemical fertilizer(N,NP,NK,PK,NPK)and long-term non-fertilization(CK).The application of organic manureincreased the content of MBC.After 17 years of long-term different fertilization,the potential mineralizable carbon(PMC)of red soil was m(184.1 mg kg^-1),significantly higher than NPKM(88.7 mg kg^-1),NPKs(48.3 mg kg^-1)and NPK(42.4 mg kg^-1),significantly higher than CK(34.6 mg kg^-1).The results showed that there was a response relationship between?SOC_stock and annual carbon input(C_input).The average conversion efficiency of SOC in red soil was11.9-14.2%.After 29 years of long-term fertilization,the soil organic carbon fixed rate(SOC_SR)of organic manureand fertilizer organic manure(M,NPKM and 1.5NPKM)was1.07 t hm^-2 yr^-1,0.64 t hm^-2 yr^-1,1.09 t hm^-2 yr^-1,respectively,which was significantly higher than that of NPKS(0.20 t hm^-2 yr^-1)and NPK(0.13 t hm^-2 yr^-1).After 11 years of long-term application of different organic fertilizer,SOC_SR was 0.80 t hm^-2 yr^-1 with NPKM3,significantly higher than 0.62 t hm^-2 yr^-1 with NPKM2,and 0.40 t hm^-2 yr^-1 with NPKM1.After 29 years of long-term fertilization,the soil organic carbon sequestration efficiency(SOC_SE)of long-term balanced fertilization(NPK)was 20.3%,which was higher than 13.1%,10.0%and 11.5%of organic fertilizer,organic manure(M,NPKM and 1.5NPKM),and NPKS 11.0%.After 11 years of long-term application of different organic manure,socse was21.1%in npkm1 treatment,16.7%higher than NPKM2 and 14.7%higher than NPKM3.The highest average sequestration rate of mineral bound soil organic carbon(MSOC)was 0.22 t hm^-2 yr^-1,followed by 0.18 t hm^-2 yr^-1 for cf POC,0.22 t hm^-2 yr^-1 for i POC,and0.03 t hm^-2 yr^-1 for ff POC.The sequestration efficiency of MSOC(7.4%)was significantly higher than that of cf POC(3.9%),i POC(2.3%)and ff POC(0.6%).Under different fertilization measures,the average sequestration rate of organic carbon at all levels was CC(2-0.2?m)0.28 t hm^-2 yr^-1,higher than SC(>53?m)0.20 t hm^-2 yr^-1,higher than CS(53-5?m)0.14 t hm^-2 yr^-1,FS(5-2?m)0.14 t hm^-2 yr^-1 and FC(<0.2?m)0.13 t hm^-2 yr^-1.The holding efficiency of CC(4.9%)was higher than that of SC(3.3%),CS(2.6%)and FS(2.2%).The highest average sequestration rate of recombinant organic carbon(HF-OC)was0.76 t hm^-2 yr^-1,followed by 0.11 t hm^-2 yr^-1 in Fr LF-OC and 0.03 t hm^-2 yr^-1 in Oc LF-OC.The sequestration efficiency of HF-OC(7.6%)was higher than that of frlf-oc(1.32%)and Oc LF-OC(0.48%).The average sequestration rate of LOC,PROC and MBC was 0.13 t hm^-2yr^-1,0.41 t hm^-2 yr^-1 and 0.06 t hm^-2 yr^-1,respectively.The sequestration efficiency of PROC(8.82%)was higher than that of LOC(5.34%)and MBC(1.17%).The application of organic manuresignificantly increased the carbon content of the stable components protected by biochemistry in the soil,which was more conducive to the sequestration of organic carbon.Long term application of organic manureis not only an important measure to improve the organic matter of red soil,but also an important way to improve the structure of red soil.Application of organic manurecan also adjust the proportion of organic-inorganic complex in red soil,which is conducive to the role of loosen soil.The CO₂,CH₄ and N₂O emissions under long-term application of organic manure,and chemical fertilizer combined with organic manure(M and NPKM)were significantly higher than those of long-term application of NPK and long-term application of chemical fertilizer combined with straw return NPKS,and there was no significant difference between the two.The CO₂,CH₄and N₂O emissions were the lowest in CK soil without fertilization.The annual cumulative CO₂ emissions in different fertilization measures were M,3835.0 kg hm^-2;NPKM,3075.1 kg hm^-2;NPK,2920.1 kg hm^-2;NPKS,2188.0 kg hm^-2;CK,1388.4 kg hm^-2.The cumulative emissions of CH₄ in different fertilization measures were NPKM,3497.9 g hm^-2;M,3306.7 g hm^-2;NPK,691.9 g hm^-2;CK,446.8 g hm^-2;NPKS,421.1 g hm^-2.The annual cumulative N₂O emissions of different fertilization measures were NPKM,13092.0 g hm^-2;M,3306.7 g hm^-2;NPK,901.4 g hm^-2;NPKS,675.5 g hm^-2;CK,337.4 g hm^-2.With the application of organic manure(M,NPKM),the carbon balance of the whole year was positive,showing a significant"sink"of carbon.Chemical fertilizer treatment(NPK),chemical fertilizer combined with straw returning(NPKS)and no fertilizer application(CK)showed obvious carbon"source"characteristics,with annual cumulative emissions of C 1.08?3.48 t hm^-2.NPK(2447.2 kg CO₂ eq hm^-2)>M(2442.8 kg CO₂ eq hm^-2)>NPKS(2142.6 kg kg CO₂ eq hm^-2)>NPKM(1471.0 kg CO₂ eq hm^-2)>CK(1268.0kg CO₂ eq hm^-2),respectively,were the highest and lowest order of npwp.The order of GHGI was CK(2.90 kg CO₂ eq kg^-1)>NPK(1.00 kg CO₂ eq kg^-1)>NPKS(0.96 kg CO₂ eq kg^-1)>M(0.34 kg CO₂ eq kg^-1)>NPKM(0.19 kg CO₂ eq kg^-1).