Effect Of Straw Incorporation On Elemental Composition And Chemical Structure Of Soil Organic Matter

Straw residue incorporation,as an important biological resource for agricultural production system,is crucial for maintaining and improving soil fertility and crop yield.In recent years,the rapid growth of soil organic matter is one reason for the crop straw incorporation.The crop straw incorporations not only promote the accumulation of soil organic matter,but also change the chemical structure of organic matter.The variations of chemical composition and structure of soil organic matter was important for sustainable utilization of agricultural natural resources.To investigate the change of SOM during the straw decomposition,two experiments was made in the field and laboratory.The chemical structure of SOM was examined by Fourier transform infrared spectroscopy(FTIR)and Solid-state nuclear magnetic resonance(NMR)spectroscopy.The main results are as follows:1)The incorporation of crop residues has increased soil organic matter and soil organic nitrogen during six-year field experiment.Compare with CK treatment,straw incorporation increased soil organic matter by 4%-16% and increased soil nitrogen by 3%-17%.Crop residues incorporation has a significant effect on chemical structure of SOM.Compare with CK,FTIR signals of amide groups(1655 cm-1/1550 cm-1)were larger in SOM of the SF1,SF2,SF3 treatments,and they were noticeably enhanced in SF2 compared with SF1.The 13 C multi CP NMR spectra analysis showed a larger proportion of O-alkyl C and a lower proportion of aromatic C in the SOM of treatments incorporating corn / wheat crop residues plus fertilizer application.In addition,the aromaticity of SOM with the addition of corn residue was larger than the aromaticity of SOM with the addition of wheat residue.2)Compare with 0 day treatment,soil organic carbon concentrations of 360 day treatment were increase by 37.8% or 48.1% under the aerobic or anaerobic condition in the simulation experiment.However,total nitrogen concentrations of the 360 d treatment were decrease by 5% and 9%,respectively.The elemental analysis showed a decrease of C/N in SOM,POM 500-53 ?m under the aerobic or anaerobic condition.In addition,the C/N of POM 500-53 ?m were larger than those of POM 53 ?m.The 13 C multi CP NMR spectra analysis showed a larger proportion of O-alkyl C and a lower proportion of alkyl C in the SOM,POM 500-53 ?m and POM 53 ?m under the aerobic condition.By contrast,there were a lower proportion of O-alkyl C and a larger proportion of alkyl C in the SOM,POM 500-53 ?m and POM 53 ?m under the anaerobic condition.Wheat straw and corn stover returning increased the relative proportion of O-alkyl C in SOM,and amide group and aromaticity in corn stover treatment was greater than those in wheat straw treatment.Wheat straw incorporation affected SOM and POM under the different condition of water management.Wheat straw incorporation can increase O-alkyl C in SOM under aerobic condition.By contrast,wheat straw incorporation can increase alkyl C in SOM under anaerobic condition.