The Effects Of Different Straw-derived Biochars And Tillage Measures On Soil Carbon

Weibei Dryland is a major production base of wheat and maize in Shaanxi Province,the long-term conventional tillage is the main soil tillage mode,deteriorating soil structure,decreasing soil organic carbon content and agricultural productivity.No-tillage and biochar amendment can improve soil properties,soil physical structure and crop productivity.The long-term field experiment and incubation experiment were applied to explore the effects of different tillage practices and different straw-derived biochar on soil organic carbon and inorganic carbon content,organic carbon forms,mineralization characteristics and soil enzyme activity,and the components and spatial variation characteristics of soil soluble organic matter（DOM）in Weibei dryland.For field experiment,based on the in Weibei dryland（started in 2007）,the study carried out the trial of four treatments:continuous cropping of wheat with no-tillage（WN）,continuous cropping of wheat with ploughing（WC）,continuous cropping of maize with no-tillage（MN）,continuous cropping of maize with ploughing（MC）.And for incubation study,we conducted four factors（soil types:conventional tillage（C）,no-tillage（N）,biochar types:wheat straw-derived biochar（WB）,maize straw-derived biochar（MB））,and three levels of biochar application(0 g·kg^-1,5g·kg^-1,20 g·kg^-1)were designed.There were ten treatments in all,which were recorded as NB0,NWB5,NWB20,CB0,CWB5,CWB20,NMB5,NMB20,CMB5,CMB20.The main results were as follows:1.Effects of different tillage practices and planting patterns on soil organic carbon and inorganic carbonTillage management had essential effects on soil organic carbon and soil humification（p<0.05）,but no significant effect on soil inorganic carbon（p>0.05）.Planting patterns and soil depth had significant effects on soil organic carbon,inorganic carbon and soil humification（p<0.05）.Soil organic carbon and soil active organic carbon decreased with the increasing of soil depth（0-100 cm）under all treatments.Compared with conventional tillage,the measures of no-tillage increased soil organic carbon storage（0-100 cm）,soil organic carbon content and active organic carbon content in plough layer（0-20 cm）under the continuous cropping of wheat;however,there was no significant difference（p>0.05）was observed under continuous cropping of maize.Compared with continuous cropping of maize treatment,continuous cropping of wheat treatment increased soil microbial biomass,microbial entropy,but decreased the content of readily oxidizable organic carbon（0-80 cm）,organic carbon storage under no-tillage practice;and increased soil microbial quotient,decreased soil organic carbon content（30-80 cm）and organic carbon storage（0-100 cm）under conventional tillage practice.For soil inorganic carbon,compared with conventional tillage practice,no-tillage treatment increased soil inorganic carbon storage and decreased soil p H（0-30 cm）under continuous cropping of wheat,however there was no significant difference under continuous cropping of maize system.Regardless of no-tillage and conventional tillage practices,the soil p H（0-30 cm）,water-soluble magnesium（60-100 cm）and inorganic carbon storage of continuous cropping of maize treatment were higher than that of continuous cropping of wheat treatment.Based on excitation-emission matrix-parallel factor analysis（EEM-PARAFAC）,Five components were extracted from soil DOM,which were UVC humic acid（C1）,humic acid（C2）,tryptophan like protein（C3）,soluble microbial metabolites（C4）and tyrosine like protein（C5）.The content of DOM decreased with the increase of soil depth,and the content in no-tillage treatment was higher than that conventional tillage practice.The proportion of surface soil humic acids was relatively larger proportion,the proportion of tyrosine like protein increased gradually,and the degree of soil humification decreased with the increase of soil depth.2.Effects of different sources of straw biochar inputs and tillage practices on soil carbonThe types of biochar had significant effects on soil organic carbon（p<0.05）.Soil types had obvious effects on CO₂ emission rate,soil organic carbon,soil inorganic carbon and soil humification（p<0.05）.The dose of biochar had significant effect on soil organic carbon and soil humification（p<0.05）,but no significant effect on soil inorganic carbon（p>0.05）.The addition of wheat straw-derived and maize straw-derived biochar increased the content of soil organic carbon,activated organic carbon,water-soluble calcium and magnesium,amount of CO₂ emission and sucrase activity,but decreased soil microbial quotient and cellulase activity,and the effects was greater with increase the dose of biochar amendment under different tillage practices.Compared with the conventional tillage practice,cumulative CO₂ emission,organic carbon content,readily oxidizable organic carbon,soluble organic carbon and microbial biomass,carbon content of no-tillage treatment significant increased under the same dose of biochar amendment.Biochar addition had no significant effect on soil p H and inorganic carbon content.With the increase of incubation time,soil inorganic carbon content decreased gradually.Based on excitation-emission matrix-parallel factor analysis（EEM-PARAFAC）,Five components were extracted from DOM,which were humic acid（F1）,terrigenous humic acid（F2）,UVC humic acid（F3）,terrigenous sedimentary humic acid（F4）and soluble microbial metabolites（F5）.The content of DOM increased under the two types biochar amendment.The content of DOM in no-tillage soil was higher than that in conventional tillage soil under the same dose of biochar application.The humification of DOM decreased in the early incubation stage under biochar amendment,however the humification of DOM increased in the advanced incubation stage.The results showed that humic acid was the main component of SOM,the relative content of microbial metabolites increased with the increase of biochar application in the early incubation stage,and the proportion of humic acid increased gradually in the terminal incubation stage.To sum up,the field experiment showed that continuous cropping of maize with no-tillage practices increased the content of soil oxidizable organic carbon,organic carbon storage and inorganic carbon storage.Indoor incubation experiment showed that the soil organic carbon,microbial biomass carbon,sucrase activity,catalase activity and microbial quotient were the highest under no-tillage practices soil and combined with maize straw-derived biochar application rate of 20 g·kg^-1.