Influence Of Biochar On The Transformation Of Additional NH₄⁺-N In Soils

Biomass-derived charcoal, also named biochar, refers to the highly aromaticsubstance remaining after pyrolysis （<700℃） of biomass under complete or partialexclusion of oxygen. Due to its characteristics of high stability against decay and highcapability of adsorption, biochar plays a significant role in decreasing carbonemission and environmental system. Also, it has been proven that biochar canimprove the physical and chemical properties of soil, increasing soil pH andwater-holding capacity and remaining the nitrogen and fertilizer in soil. In this thesis,a series of experiments were carried out to study physico-chemical properties ofbiochar and the effects of two kinds of biochars on NH₄⁺-N transformation. The mainresults of this thesis are as follows,1) The experiment about the influence of biochar on NH₄⁺-N nitrification in twodifferent soils indicated that biochar greatly reduced NH₄⁺-N concentration in the KClextract of Gleyi-Stagnic Anthrosols soil by9%³5%while NO₃^--N concentration inthe KCl extract was slightly reduced by7.5%. As a contrast, biochar slightly reducedNH₄⁺-N concentration in the KCl extract by5%²2%and had little effect on NO₃^--Nin the Argi-Udic Ferrosols soil. Limited NH₄⁺-N nitrification to NO₃^--N was observedin both Gleyi-Stagnic Anthrosols and Argi-Udic Ferrosols soils in such a short term of4weeks.2) The experiment about influence of biochar on NH₄⁺-N in different cultivationways indicated that under70%WHA and100%WHA moisture conditions, biocharreduced NH₄⁺-N concentration by35%and13%, respectively in Argi-Udic Ferrosolssoil with addition of200mg/kg NH₄⁺-N. However, the NO₃^--N concentrationremained unchanged. In the absence of extra NH₄⁺-N, the NO₃^--N concentrationsignificantly increased by37.5%with the moisture content increasing from70%to100%, which even exceeded the corresponding treatment with extra NH₄⁺-N. However,5%straw biochar could eliminate the increase and remain NO₃^--N contentat a low level, so as to avoid the nitrogen fertilizer being leached in the form ofNO₃^--N.3) The experiment about influence of biocharon NH₄⁺-N via soil microbialactivity indicated that both5%straw biochar and5%manure biochar reduced NH₄⁺-Nconcentration in the KCl extract of Gleyi-Stagnic Anthrosols soil by34%and57%,respectively, with42%and57%of the reduction attributed to microbial activity,respectively. The5%straw biochar and5%manure biochar reduced NH₄⁺-Nconcentration in the KCl extract of Argi-Udic Ferrosols soil by12.6%and14%,respectively.4) The experiment about the influence of biochar on NH3volatilization viachange in soil pH indicated that5%straw biochar elevated pH of both Gleyi-StagnicAnthrosols soil and Argi-Udic Ferrosols soil, resulting in the accumulated NH3volatilization in Gleyi-Stagnic Anthrosols and Argi-Udic Ferrosols soil as much as7.8and1.7times the untreated soil, respectively. Similarly5%manure biochar elevatedpH of both soils, resulting in the accumulated NH3volatilization in Gleyi-StagnicAnthrosols and Argi-Udic Ferrosols soils as much as14.4and5.6times.5) The experiment about the influence of biochar on NH₄⁺-N adsorptionindicated that5%straw biochar could improve adsorption ability of Gleyi-StagnicAnthrosols soil, but it had no effect on Argi-Udic Ferrosols soil.5%manure biocharcould increase adsorption ability of Gleyi-Stagnic Anthrosols soil and Argi-UdicFerrosols soil when the initial NH₄⁺-N were <80mg L-1and <60mg L-1,respectively.