Decomposition Characteristics Of Organic Materials And Their Effects On Organic Carbon In A Semiarid Soil Under Plastic Mulch And Drip Irrigation

Inappropriate use of organic materials?OMs?leads not only to waste of resources,but also to environmental pollution.In order to improve the efficiency of recycling processes of OWs,various studies indicated that the OMs can be effectively employed as soil modifiers or fertilizers.Poor soil,a thin arable layer,and drought resistance have restricted the crop production in the Tumuji town,located in Inner Mongolia.Plastic mulched drip irrigation technologies change the microenvironment of soil?such as water,nutrients,air,and temperature?,and are particularly suitable for popularization in the semiarid areas of western China.However,plastic mulched drip irrigation technologies promote the carbon mineralization in long term.The application of OMs can supplement carbon source for soil and effect the organic carbon pool.Moreover,the effects of OMs on organic carbon pool were closely related to the types and properties of exogenous OMs.Therefore,the two-year experiments involved six treatments:chicken manure?CM?,sheep manure?SM?,mushroom residue?MR?,maize straw?MS?,fodder grass?FG?,and tree leaves?TL?,while an unamended soil?no OWs?was used as control.The results of decomposition characteristic of OMs are as follows:?1?In 540 d,the decomposition rates of CM?71.55%?,SM?68.21%?,and MS?68.16%?were higher than MR?58.64%?,FG?55.28%?,and TL?47.95%?.?2?The carbon mineralization potentials?C₀?of MS?6.11?and?4.75?were higher than other OMs.The constant of carbon decomposition rate?k₀?of MS?0.0194?was the highest,whereas that of TL?0.0117?was the lowest.?3?The trends of water-soluble organic matter?WOM?contentsofOMsindecompositionprocesswere“decline-increase-decline”.MS could inform more WOM in decomposition process.?4?In decomposition process,the trends of cellulose contents were quickly declined and then tended to stable,and the trends of lignin contents were quickly increased and then tended to stable.MS could inform more lignin contents in short time.?5?The results of FTIR and DTA showed that aromatic,carbohydrate,and polysaccharide substances of MR,CM,and MS increased in decomposition process,whereas those of TL,FG,and SM reduced.The results of decomposition characteristic of humic-like substance?HSL?derived from OMs are as follows:?1?HSL and humic acid-like?HAL?contents exhibited the trends of“decline-increase-decline”.MS could inform more HSL.?2?E₄/E₆ ratios and?logK values of HAL and fulvic acid-like?FAL?exhibited the trends of“decline-increase-decline”.?3?The results of FTIR showed that,in decomposition process,the aliphatic C of HAL increased,and aromatic C of HAL of MR,CM,SM,and MS enhanced.The results of the effects of OMs on soil organic carbon components are as follows:?1?The present two-year field experiments showed that OM treatment led to a continuous increase in the SOC,LC,RC,DOC,MBC,EOC and CPMI parameters,along with a decrease in the Kos values.?2?Higher SOC,RC,and RC/SOC?P<0.01?were achieved for the treatments amended with TL and MS compared to the other OMs.The LC,DOC,EOC,and CPMI values were higher in the case of treatments amended with CM,SM,and MS,whereas the K_oss values were lower.The results of the effects of OMs on soil humus components and structures are as follows:?1?Treatment with OMs led to increased levels of humic acid?HA?and fulvic acid?FA?.Higher HA and FA contents?P<0.05?were achieved for TL and MS compared to other OMs.?2?Compared to the control,the E₄/E₆ ratios and?logK values of HA and FA were lower for TL,FG,and SM,and followed the order TL<FG<SM.The E₄/E₆ ratios and?logK values of HA and FA were higher for MS,CM,and MR,and that of HA followed the order MS>CM>MR,and that of FA followed the order CM>MS>MR.?3?The results of elemental analysis,FTIR,EEM fluorescence,and ¹³C CPMAS NMR showed that the aliphatic C/aromatic C ratios,and fluorescence intensities of peak A and peak B of HA and FA were lower for TL,FG,and SM,whereas higher C/H ratios were obtained.The aliphatic C/aromatic C ratios and fluorescence intensities of peak A and peak B of HA and FA were higher for MS,CM,and MR than for the control,while lower C/H ratios were observed.The application of TL was the most effective for enhancing the aromatic C component and making the structure complex and stability,whereas that of MS and CM was the most effective for enhancing the aliphatic C component,and making the structure of HA and FA simple,respectively.The results of the effects of OMs on the relationships between soil organic carbon and maize yields are as follows:?1?The present two-year field experiments showed that OM treatments increased yields,and the yields for MR,CM,and MS were higher than other OMs.?2?Yield showed a positive relationship with MBC,LC,DOC,and LC/SOC,whereas showed a negative relationship with K_oss value.?3?Yield showed a positive relationship with E4/E6 ratios,?logK values,and aliphatic C/aromatic C ratios of HA and FA.?4?SOC and RC contents showed a positive relationship with lignin,polyphenol,lignin/N ratio,WOM,WHA,HSL,and HAL.In conclusion,the chemical components,humic-like substances,and structures of different OMs were very different.There were also large differences among the decomposition characteristics of OMs in semiarid soil under plastic mulched drip irrigation conditions.The two-year field experiments showed that the application of TL and MS were more effective for improving the soil organic carbon and humus accumulation.The application of TL made the structure of HS complex and stability,and was the most effective for organic carbon sequestration.The application of MS made the structure of HS simple,and effectively accumulated the labile organic carbon,and thus was the most effective for organic carbon update.