Simulation Study On Effects Of Biochar Amendment On Retention And Transformation Of Soil Nitrogen

Soil nitrogen(N) is the most important element for crop growth and yield improvement. However, excessive application of N fertilizers may pose a great threat to the quality of surface- and groundwater, and affects soil fertility and the quality of soil environment. Biochar has the ability to retain soil nitrogen and reduce nitrate-N loss, but it is not cleared that the retention and transformation mechanism of biochar on soil nitrogen. Therefore, study the mechanism has become a particular urgent need to increase soil nitrogen use efficiency and reduce N loss. In the present study, different types of biochar were produced from wheat-straw, corn-straw and peanut-shell pyrolized at 400℃, 500℃, 600℃, 700℃. Some parameters, yield, elements, ash contents, pH value, cation electricity capacity and specific surface area of biochar were determined. In this article, the adsorption ability of inorganic N in solutions by the above produced biochars using the adsorption experiment. Meanwhile, nitrate N(NO3--N) retention at different soil depths using multi layered soil columns at biochar adding rates of 0 biochar, 2% biochar, 4% biochar and 8% biochar(biochar/soil) plus soil microbial biomass and key bio-process using incubation experiment at biochar adding rates of 0 biochar, 1% biochar, 2% biochar and 4% biochar. Concequently, we could clarify the mechanism of retaining N by biochar. The main results are as follows:(1) Feedstock types and pyrolysis temperature greatly influenced the biochar chemical and physical characteristics. The results showed that biochar yield and contents of N, hydrogen and oxygen decreased as pyrolysis temperature increased from 400°C to 700°C, whereas contents of ash, pH and C increased with greater pyrolysis temperature. The values of electrical conductivity and cation exchange capacity(CEC) in corn-straw biochar(C-BC) was much higher than wheat-straw biochar(W-BC) and peanut shell biochar(P-BC), while the surface area was much smaller than them in each of the pyrolysis temperature.(2) All biochars could sorb substantial amounts of ammonium nitrogen(NH4+-N), and the sorption characteristics were well f itted to the Freundlich isotherm model. The ability of biochars to adsorb NH4+-N followed: C- BC > P-BC > W-BC, and the adsorption amount dec reased with higher pyrolysis temperature. The ability of C-BC to sorb NH4+-N was the highest because it had the largest cation exchange capacity(CEC) among all biochars(e.g. C-BC400 adsorbed 2.3 mg NH4+-N g-1 in solutions with 50 mg NH4+ L-1). Compared with NH4+-N, none of NO3--N was adsorbed to biochars at different NO3- concentrations. Instead, some NO3--N was even released from the biochar materials in this present study at high NO3- concentrations(>300 mg NO3- L-1).(3) Biochar effectively increased the water holding capacity of the soil. As a result, addition of biochar reduced the leachate volume by 7.0% in 2% biochar, 12.0% in 4% biochar and 19.2% in 8% biochar compared with the control without addition of biochar. It was obvious that NO3--N leaching loss mainly occurred at the initial leaching stage during the leaching process. Leaching of NO3--N amounted to 49.1 mg(2% biochar), 44.1 mg(4% biochar), 38.4 mg(8% biochar), with a reduction by 14.9%、23.5%and33.3%comparedwiththecontrol,respectively.meanwhile,soilmicrobialbiomasscouldimprovedundercorn-strawbiocharamendmentandsoilmicrobialbiomasscarbonandnitrogencouldincreasedby7.1%-21.0%,18.7%-51.8%afteradding2%-8%biochar,respectively.(4)soilphvalueswerebothincreasedinredsoilandblacksoilbyapplicationbiocharatratesof0biochar,1%biochar,2%biocharand4%biocharofsoilmass.especially,withamendmentofbiocharatratesof4%couldsignificantlyincreasesoilphvaluesby17.2%inredsoil.however,soilphcouldmerelyincreasedby2.7%inblacksoil.meanwhile,soilorganicmattercouldalsobeincreasedby4.0%-85.4%,17.8%-58.4%inredandblacksoil,respectively.similarlytothetrendoforganicmatter,soildissolvedorganiccarboncouldbeimprovedby5.7%-25.3%inblacksoilcomparedwithtreatmentswithoutbiochar.however,thedissolvedorganiccarboncouldreduce34.0-154.5mgkg-1afterapplicationbiocharinredsoil.biocharamendmentcouldincreasesoiltotalncontentsinthesetwotypesofsoils.however,theabilityofretaininginorganicnbybiocharwasinfluencedbysoiltypes.additionofbicoharhadnosignificantdifferenceonredsoilnh4+-nandno3--n.meawhile,ithadnosignificantdifferenceonblacksoilno3--ncontentsunderdifferenttreatments.interestingly,soilno3--ncontentscouldbereducedwithamendmentofbiocharinblacksoil.soilmicrobialbiomasscarbonandnitrogencouldbeinhibatedinredsoil.however,soilmicrobialbiomasscarboncouldbeimprovedby12.0%-16.4%inblacksoilafteraddingbiocharandmicrobialbiomassnitrogenshowednosignificantdifferenceattheendstageofincubationexperiment.soilrespirationratewasincreasedinblacksoilbutreducedinredsoil.interestingly,thetotalcontentsofplfawouldbepromotedwithbiocharamendmentinblacksoil.incontrast,thetotalcontentsofplfawouldbeinhibatewithapplyingbiocharinredsoil.