Effects Of Straw Returning Methods On Soil Humus Accumulation Based On Meta Analysis And Simulation

Straw returning is an important measure to take into account straw resource utilization and soil carbon sequestration and fertilizer cultivation.The contribution of soil humus composition and quantity to soil carbon storage and its stabilization mechanism is an important content of carbon cycle research in agricultural ecosystem.Many studies have been conducted on the composition and quantity of soil humus after straw returning to the field.However,due to the differences in returning mode,straw properties,soil and climatic conditions,the influence of straw returning to the field on soil humus composition and quantity has great heterogeneity.In this study,Meta analysis and field simulation were combined to quantitatively analyze the effects of straw returning on soil humic acid,fuluric acid and humin carbon(HA-C,FA-C and Hu-C)contents,and the differences of straw returning mode,straw properties,soil and climate conditions on the contents of HA-C,FA-C and Hu-C.The literature used in the meta-analysis was mainly searched in CNKI,Web of Science,Google Scholar and other databases,and 689 sets of observations from 44 valid publications published by Chinese scientific research institutions were obtained after screening.The effects of straw returning on soil HA-C,FA-C and H were quantitatively evaluated under different returning methods(length of returning,frequency of returning,amount of returning,contact degree between straw and soil,depth of returning,nitrogen application amount next year),straw properties(straw type,straw morphology,straw carbon-nitrogen ratio),soil conditions(soil type,soil p H,soil depth)and climatic types The influence of u-C content.Six treatments were set up in the field microzone simulation experiment,which were as follows: No straw(Na1),straw mulch(Nb),straw and surface soil evenly mixed(Nc1),straw(Na2),straw and subsurface soil evenly mixed(Nc2),quadrupling straw and subsurface soil evenly mixed(Nd)were applied to surface soil in surface soil.The sampling time was 30 d,180d,360 d and 720 d.To explore the effects of different straw application methods on soil humus composition,cumulative effect and molecular structure characteristics of HA.The results of meta-analysis showed that:(1)straw returning significantly increased soil humus carbon content,which increased HA-C content by 30.3%,FA-C content by 10.4%,and Hu-C content by 16.7%.(2)The contents of HA-C and Hu-C in soil increased with the increase of time after straw application,while the contents of FA-C did not change significantly with the increase of time.The contents of HA-C,FA-C and Hu-C in soil increased more with successive returning of straw.Applying half amount of straw(2500～7500kg/ha)resulted in the best accumulation effect of HA-C,FA-C and Hu-C in soil,and mixed returning had the best accumulation effect of HA-C and Hu-C in soil,while mulching and mixed returning had the greatest increase of FA-C in soil.Straw returning to the soil surface(0～20 cm)increased the carbon content of soil humus components more.The higher the nitrogen application rate,the more the accumulation of HA-C and Hu-C,and the change of FA-C was not obvious.(3)The more alkaline soil is more conducive to the accumulation of humic acid and humin,while the more acidic environment is more suitable for the accumulation of fulvic acid.The influence of straw returning to the field on the accumulation of humus carbon varies in different soils and different climates.(4)There was a negative correlation between the carbon accumulation of straw C/N and the carbon accumulation of each component of humus material.Compared with the straw returned into pellets,the accumulation of FA-C and Hu-C could be promoted more by grinding and returning.The accumulation of HA-C and Hu-C of straw returned to the field from different sources was different,but there was no significant difference for different sources of FA-C.(5)The important factors affecting the accumulation of HA-C,FA-C and Hu-C are not identical,and straw C/N is a common important factor affecting the humus carbon.The simulation results showed that:(1)Both straw mulching and mixed mulching could increase the SOC content of surface soil,and the depth of enrichment also significantly increased the SOC content of subsurface soil.There was no significant difference in the conversion efficiency of straw residues into SOM in different ways,and returning straw residues to the surface was more conducive to the conversion of straw residues into SOM.Both straw mulching and straw mixing caused the accumulation of humus in the surface soil,and the accumulation of HA in the surface mixture was faster.The accumulation of humus substances in subsurface soil is better than that in deep mixing.The conversion of humus substances in deep mixing is not as effective as that in mulch and surface mixing.However,more humus substances can be formed when straw is enriched deep.(2)One-off application of straw enhanced the molecular structure of soil HA aliphatic,oxidation degree decreased,hydrophobicity increased,polarity decreased,thermal stability decreased,and gradually developed into the original soil HA or aromatization after 360 d.This phenomenon was most obvious in the soil HA under the surface mixing and enrichment depth.