Effects Of Long-term Fertilization On Soil Organic Carbon Content And Stability In Paddy

Soil carbon pool has huge carbon sequestration potential,most of which exists in the form of organic carbon.Increase soil organic carbon content and stability will contribute to the reduction of greenhouse gas emissions.The paddy soils occupy a large area in our country,which plays an important role in promoting carbon sequestration and mitigating climate change.Fertilization is a necessary way of modern agricultural management.Reasonable application of fertilizers can not only provide crops with the necessary nutrients to maintain optimal growth,but also enhance soil organic carbon sequestration and alleviate global climate change.From Jiaxing National Soil Quality Observation and Research Station in Zhejiang Province,soil samples of 9 long-term(30 years)fertilization treatments(No fertilization(CK1);Noncultivation(CK2);Application of organic fertilizer(M);Organic fertilizer and nitrogen fertilizer(MN);Organic fertilizer and nitrogen,phosphorus,potassium fertilizer(MNPK);Nitrogen fertilizer(N);Nitrogen and phosphate fertilizer(NP);Nitrogen and potassium fertilizer(NK);Nitrogen,phosphorus and potassium fertilizer(NPK))were taken and analyzed to explore the effects of different fertilization treatments on the content,composition and stability of organic carbon in barley-rice rotated soils,and to reveal the mechanism of these influences,providing scientific basis for a better management of fertility and organic carbon pool in farmland soils.The main research results are as follows:(1)Compare to the control treatment without fertilization(OK1),soil organic carbon content in CK2 treatment increased by 64.49%.Fertilization affected soil organic carbon content.Application of organic fertilizer without and with chemical fertilizer had a stronger promoting effect on soil organic carbon accumulation,increasing by 48.60%66,36%.Application of chemical fertilizer could basically maintain soil organic carbon level.Compared to treatments without chemical phosphrus(MN,N,NK),treatments with phosphrus(MNPK,NP,NPK)decreased soil organic carbon content.(2)Compared with no fertilizer treatment(CK1),both light fraction(LFOC)and heavy fraction(HFOC)increased in the treatments of noncultivation and organic fertilization without and with chemical fertilizers,in which HFOC increased more than LFOC.The increase of LFOC is mainly due to the increase of particulate organic carbon(POC),whereas the increase of HFOC is mainly caused by the increase of humin-type organic carbon(HFHM).The change of total organic carbon in soil treated with chemical fertilizer but without phosphorus was mainly manifested in the increase of LFOC content,especially the increase of colloidal organic carbon(OC 胶),while the HFOC decreased slightly.For treatments of chemical fertilization with phosphorus,fractions of soil organic carbon shown little change compared with control without fertilization.(3)Fertilization will reduce soil carbon age and weaken the overall stability of organic carbon.The age of soil organic carbon followed the order of no fertilization treatment>chemical fertilizer application(no phosphorus)treatment>chemical fertilizer application(with phosphorus)treatment>organic-inorganic fertilizer combination(without phosphorus)treatment>organic fertilizer treatment and noncultivation.Base on the soil carbon age and organic carbon content,the soil organic carbon can be divided into original stable organic carbon and newly added organic carbon,and it was assumed that in the non-fertilized control treatment(CK1),100%of soil organic carbon is original stable organic carbon.The proportion of original stable soil organic carbon in the noncultivation treatment and organic fertilization treatments was 43.91-54.17%,while the proportion of original stable soil organic carbon in the soil treated with chemical fertilizers was more than 60%,and the proportion of original stable soil organic carbon in the soil treated with phosphorus was lower than that without phosphorus.Fertilization especially application of organic fertilizer induced priming effect,promoted degradation of original stable organic carbon.In the meantime enhanced accumlation of newly added organic carbon.(4)There was no obvious change between different forms of Fe and Al oxides in soil under different fertilization treatments.Via addition of phosphate,it shows there is a strong competition between soil organic matter and phosphate on the surface of oxides minerals.With the increase of phosphate,the desorption of soil organic matter increases.The particle size of soil oxide minerals applied with organic fertilizer is the smallest,especially in MNPK treatment,followed by the soil treated with chemical fertilizer(with phosphorus)and noncultivation treatment.The particle size of soil oxide mineral nanoparticles under chemical fertilizer(no phosphorus)treatment is the largest.According to the calculation,the thickness of organic matter layer around oxide minerals is significantly positively correlated with the particle size of oxide minerals.The smaller is the mineral particle size,the thinner the layer of soil organic carbon around the particles is.Due to the increase of overall surface area,more organic matter is closely associated with oxide minerals and is protected,suggesting that the carbon sequestration effect of organic fertilizer is better than other treatments.Based on the above results,it is concluded that for the barley-rice rotated soil with different fertilization for 30 years,application of organic fertilizer and combined application of organic-inorganic fertilizer could significantly increase soil total organic carbon content,but it enhanced degradation of original stable soil organic carbon due to priming effect,therefore decreased the overall stability of total organic carbon.Application of chemical fertilizer could only basically maintain the level of soil organic carbon.Application of phorphrus decreased soil stable organic carbon further.When considering the increase of soil organic carbon content,protection of original stable carbon,and maintaining their stability,application of organic fertilizer in combination with chemical nitrogen fertilizer(MN)gives the best result.