Particle Size Fractionation Of Chemical Characteristics Of Organic Matter Among Three Typical Soils In The North And South Of China And Its Response To Long-term Organic Fertilization

Soil organic matter（SOM）plays a fundamental role in soil fertility,sustainable development and global carbon cycle.At present,the chemical characteristics of SOM are poorly understood,especially the spatial differentiation of SOM chemistry in different particle sizes among soil types and its response to long-term organic fertilization.This study takes black soil,fluvo-aquic soil and red soil as research objects and three fertilization treatments（NPK fertilization,NPK + straw（NPKS）fertilization,NPK + manure（NPKM）fertilization）were selected in the long-term positioning experiment.Based on physical fractionation（coarse particulate OM,c POM,>250 μm;fine particulate OM,f POM,53 μm–250 μm;and mineral-associated OM,MOAM,<53 μm）,the chemical characteristics of SOM were analyzed by pyrolysis-gas chromatography-mass spectrometry.The contents of soil organic carbon（SOC）and total nitrogen（TN）were determined by elemental analyzer,and then calculate the C/N,H/C,N/C,O/C,and C oxidation state by using the compound element composition.The particulate differentiation of SOM chemistry among three typical soil types and its response to long-term organic fertilization were basically clarified.The main research results were as follows:（1）Compared with the NPK fertilization treatment,the mass proportion of different fractions in the three soil types changed less with organic fertilization,but the NPKM fertilization significantly reduced the mass proportion of MAOM in black soil and red soil.At the particle size level,the mass proportion of MAOM in three soils was the largest（>75%）,c POM followed,and f POM were the least.（2）Compared with NPK treatment,NPKM significantly increased the content of SOC in black soil and red soil（35%–60%）,and significantly increased the content of MAOM（40%）.At the particle size level,the distribution pattern of SOC content in the three types of soils was consistent,and all of them were MAOM > c POM > f POM.Compared with NPK treatment,NPKM significantly increased the content of TN in black soil and red soil（96.29% and 31.95%）,while NPKS only increased the content of TN in black soil（92%）.At the particle size level,the TN content in the fluvo-aquic soil increased with the decrease of particle size,and the TN content in the other soil was the mineral bound component from high to low were MAOM > c POM > f POM.Compared with NPK treatment,long-term organic fertilization had less effect on C/N in fluvoaquic soil and red soil,and only significantly reduced C/N in black soil（13%–40%）.At the particle size level,C/N of black soil and fluvo-aquic soil reduced with the decrease of particle size,and the decomposition degree was higher with the decrease of particle size.However,the C/N of f POM in red soil was higher,indicating that the decomposition degree was weak.（3）The chemical characteristics of SOM were mainly controlled by soil type,following by particle size and fertilization.The chemical composition of different soils has different proportions.For example,aliphatic compounds are the most in fluvo-aquic soil（60%–90%）,while nitrogenous substances are more in black soil（>70%）.The content of phenolic compounds in red soil is high（5%–18%）.At the particle size level,MAOM is relatively enriched in N-containing compounds,while the POM is relatively enriched in aliphatic compounds,aromatic compounds,lignin and polysaccharides.Organic fertilization decreased the H/C of f POM in black soil,and increased the N/C and carbon oxidation state of whole soil and MAOM.The O/C of f POM in fluvo-aquic soil is decreased.Only the addition of NPKM decreased the H/C of f POM,while the O/C,N/C and carbon oxidation state increased in red soil.In terms of particle size,f POM has higher H/C,and MAOM has higher N/C.（4）The source composition of compounds was different among different soils,and the effect of fertilization was the least.Microbial sources were dominant in the three types of soils,accounting for about 50%–70%.In the black soil,NPKS and NPKM fertilization significantly increased the plant derived compounds by 75.99% and 91.26%,respectively,and decreased the microbial derived compounds by 19.51% and 20.52%,respectively.NPKS fertilization in red soil significantly increased the bulk soil and MAOM of plant derived compounds by 40%–50%.At the particle size level,the plant derived compounds are mainly concentrated in POM.