Effects Of Different Kinds Of Organic Materials Application On Organic Carbon And Humus Composition Within Different Aggregate-size Fractions In A Black Soil

Based on field location experiment with organic fertilization in a black soil?2011-2015?,eight kinds of treatments were set up in the experiment,no fertilizer?CK?and single application of mineral fertilizers?NPK?,NPK with four kinds of organic manure?NPK+compost manure,NPK+chicken manure,NPK+cow manure,and NPK+pig manure?,NPKS?mineral fertilizers plus maize straw?,NPKB?mineral fertilizers plus maize straw-derived biochar?.Design 3repetitions,planting crops for corn.The effects of different kinds of organic materials application on organic carbon?C?concentrations and humus composition in bulk soil and its different size aggregate fractions were studied.In this study,the quantitative and qualitative characteristics of humic-like substances?HLS?isolated from MS and MSB were described using chemical and spectroscopic methods.The present study revealed the essential differences between humic-like substances from MSB and raw MS.And NPKS and NPKB was conducted to evaluate the effects of maize straw and its derived biochar application on the size distribution and water stability of soil aggregates,and the chemical compositions of organic and humic C in water-stable aggregate fractions in a Mollisol of northeast China.1.The results showed that,compared with CK and NPK,the application of organic manures in combination with chemical fertilizers increased significantly?P<0.05?the concentrations of organic C,humic acid C?HAC?and humin C?HUC?in bulk soil;Meanwhile,the concentrations of organic and humic C within different size aggregate fractions also increased after the combined application of organic manures with chemical fertilizers compared to CK and NPK treatments,with significant increase for organic C,HAC and HUC within different size aggregate fractions following compost manure application;Compared with different types of organic manures,the concentrations of organic C,HAC and HUC were higher for compost manure than for other organic manures treatments,with significant difference between compost manure and cow manure treatments.With respect to other organic manures treatments,>0.25mm aggregate-associated organic C concentration was higher after the application of compost manure and cow manure,with significant difference between compost manure and cow manure with chicken manure treatment for 2⁰.25 mm aggregate fraction;Moreover,the concentrations of HAC and HUC in 2⁰.25 mm aggregate fraction were significantly higher for compost manure than for pig manure treatment,whereas the concentration of HAC 0.25⁰.053,<0.053 mm aggregate fraction were significantly lower for compost manure than for chicken manure treatment.2.In this study,the quantitative and qualitative characteristics of HLS isolated from MS and MSB were described using chemical and spectroscopic methods.Compared with raw MS,the carbon contents of HLA and FLA fractions in MSB were lower,while the carbon content of HUL was higher.The ratios of H/C,alkyl C/O-alkyl C,aliphatic C/aromatic C and hydrophobic C/hydrophilic C were 1.2,1.1,0.8 and 2.6 for HLA from MSB,and 1.5,0.2,2.1and 0.7 for HLA from MS,indicating that the aromaticity,alkylation and hydrophobicity degrees of HLA were higher in MSB than in MS.With respect to HLA,the elemental composition of HUL was more similar to their respective feedstock.The HUL in MSB was more aromatic and less polar than that in MS.3.Compared with CK and NPK treatments,the proportion of macroaggregates?>0.25 mm?[mainly large macroaggregates?>2 mm?]increased whereas the proportions of microaggregates?0.25-0.053 mm?and silt+clay fractions?<0.053 mm?decreased in NPKS and NPKB treatments,resulting in the mean weight diameter?MWD?and geometric mean diameter?GMD?of soil aggregates were higher under NPKS and NPKB than under CK and NPK treatments.The concentrations of organic and humic C in bulk soil and aggregate fractions were also generally higher under NPKS and NPKB than under CK and NPK treatments.The treatment effects were more obvious for NPKB than for NPKS.With respect to other treatments,NPKB treatment significantly increased the ratios of macroaggregate-to microaggregate-associated organic C as well as humin C.The solid-state ¹³C cross-polarization magic-angle-spinning?CPMAS?NMR spectra of small macroaggregates?2⁰.25 mm?and its humic acid fraction showed that NPKS treatment did not alter groups,in contrast,NPKB treatment obviously decreased the proportions of alkyl C and O-alkyl C but increased the proportion of aromatic C,resulting in the alkyl C/O-alkyl C and hydrophobic C/hydrophilic C ratios were higher whereas the aliphatic C/aromatic C was lower under NPKB than under other treatments.These findings indicated that the application of MSB enhanced soil aggregate stability and aggregate-associated organic and humic C concentrations.Biochar C was preferentially incorporated into macroaggregates and its humin fraction with respect to microaggregates.Moreover,the molecular structure of small macroaggregates and its HA fraction became more stable,hydrophobic and aromatic.