Effects Of Biochar Application On Soil Improvement On The Loess Plateau

Loess Plateau is the most serious soil erosion region in the world. The localagricultural production and ecological restoration has been limited in some extent by poorsoil fertility, water shortages, and serious erosion. The improvement effects of biocharapplication on soil properties and plant growth has become a new research focus.In this study, five typical soil types (Lou soil, Dark Loessial soil, Loessal soil,Shahuang soil, Aeolian sandy soil) spread across the Loess Plateau and one type of biochar(made from sewdust) were chosen as the test materials for the incubation and fieldexperiments. Biochar was mixed with the soils at the rates of0、4、8、16g/kg.0-10cm and10-20cm layers were sampled separately four times in the experiment period fromNovember2010to November2012. Soil pH, CEC, organic carbon content, bulk density,soil aggregates, soil water properties were characterized. Simulation rainfall experimentwas done with the soil incubated with18months to indicate the effect of biocharapplication on soil erodibiltiy. The main research findings are shown as follows:(1) Effects of biochar application on soil pH and CEC were determinated. Impacts ofbiochar application on soil pH were influenced by the basic properties of biochar and theamended soil. The pH of the alkaline soils in the Loess Plateau would not be increased bythe application of biochar with lower pH value. The results of the incubation experimentshowed that biochar application has the potential abilitiy to restrict soil salinization processin some extent, the restrct effcet would be better in the Aeolian sandy soil with low ferlity.Biochar appliction didn’t increase soil CEC significantly in all the five soils in theexperiment. The steady increasing effcet on soil CEC was only shown in the Aeolian sandysoil with lower fertility. The higher biochar application rate would get higher soil CEC. Inthe two years experiment period, the oxidation of biochar didn’t effectively promote soilCEC increasing. (2) Effects of biochar application on soil microbial biomass canbon, soil organiccarbon and soil density fraction were determinated. Biochar application would increase soilmicrobial biomass carbon content. The results were shown in both the incuabtion and fieldexperiment and were more significant in the longer experiment period. The increasingeffect of soil microbial biomass by biochar application was much better in the Aeoliansandy soil, followed by the Shahuang soil, Loessal soil and Lou soil, Dark loessial soil.The determined soil orgnic carbon contents in the soil and the hervy fraction were bothincreased significantly by biochar application. Because that biochar contains some part ofheavy fraction, soil organo-mineral complex content, which was determined by heavydensity fraction and dichromate oxidation (external heat applied) method, couldn’t be usedas the indice to show the soil improvement effect of biochar application.(3) Effects of biochar application on soil bulk density and soil aggregates weredeterminated. Biochar application showed the trend to decrease the soil bulk density, whilethe significant decreasing effect only shown in Aeolian sandy soil. Biochar applicationdidn’t influece the soil aggreagate distribution in the air-drying sieving. However, biocharapplication showed the improvement effect on soil aggregates stability. The improvementeffects were shown more obviously and earlier in the Lou soil and Dark loessial soil, whilein the Shahuang soil and Loessal soil the increasing tendency was shown n the secondexperiment year.(4) Effects of biochar application on soil water properties were determinated. Biocharapplication didn’t significantly influence the soil water hold capacity and soil saturatedhydraulic conductivity in Lou soil, Dark loessial soil, Shahuang soil and Loessal soil. Butit can increase the soil water hold capacity and decrease saturated hydraulic conductivity ofAeolian sandy soil with coarse-texture and amounts of macropores. The influence effectwas better when higher biochar application rate was used. The decreased soil hydraulicconductivity by biochar application in the sandy soils was benefit to store the rainfall in thesurface layer and supply the plant growth.(5) Effects of biochar application on soil erosion in two kinds of rainfall event weredeterminated by simulation rainfall experiment. The results showed that biocharapplication can weakly delay the time to runoff. In the first rainfall event with air-dryingsoil, the runoff amount wasn’t decreased in the biochar amended soils. Becaused of the increased soil stability, the sediment amount were not incrased. The restrain effect ofbiochar applicaion on soil shrinkage lead to the better soil structure and was conducive tothe increase of soil infiltration. The second rainfall event showed that soil erosion chouldbe decreased by biochar application in Dark loessial soil, Shahuang soil and Loessal soil.Biochar application could increase soil stability and decrease soil erosion in the LoessPlateau.From the study, we found that biochar appliation has the better improvement effect onthe coarse-texture and unfertility soils. The improvement effect was limited with thebiochar application rate of the study, and higher biohcar application rate had the tendencyto get better improvement effect. Higher application rate of biochar or application withother materials would get better soil amendment effect in the Loess Plateau. In therelatively short experiment period, biochar application didn’t show the steadyimprovement effect. Long period montoring system should be set up to assess the influenceprocess and comprehensively assess biochar application effects on soil properties.