The Study Of Straw And Biochar Returning On Soil Quilaty And Soil Carbon Content In Guanzhong Plain

To improve the soil organic matter quatity and soil structure, and to develop theyield productivity in Guanzhong Plain, a filed research including3treatments wasestablished in2008-06to the2010-10in Sanyuan Experiment Station of NorthwestA&F University. In addition, two incubation experiments were carried out to assess thecharacteristic of biochar decomposition in the Guanzhong Plain. The results were asfollows.1. Investigating the effects of different straw returning models on soil fertility andcrop yield is very vital, and can provide references for theory of sustainable agriculturaldevelopment in continuous winter wheat-summer maize rotation system area. Theresearch had been carried out continuously during2008to2010, for two years, inGuanzhong Plain. There were four treatments including3straw management models,namely, T-1: maize straw mulching-high wheat stubble retention, T-2: maize strawchopping-high wheat stubble retention, T-3: maize straw chopping-wheat strawchopping, and no maize and wheat straw returning was designed as CK. The soil totalcarbon storage (C_T), soil labile carbons (C_L) storage, soil carbon management index(CMI) and soil chemical fertilizer content were determined. And the annual crop yieldwas recorded. Straw returning treatments showed obvious influence on C_T, C_L, CMI,soil total P, soil NO3-, soil available K content and annual crop yield within2years. Thedifference among the three straw mulching models showed the trend of T-3> T-2> T-1for C_T, C_Lstorage, and CMI; whereas, the observed trend was T-2> T-3> T-1in thecase of annual grain yield and available K contents in soil; different straw returningmodel did not show significant effect on other soil chemical fertilizer content.Theresults indicate that, T-2is the optimized straw management in the winterwheat-summer maize annual double cropping areas in Guanzhong plain of China.2. An incubation experiment was carried out on maize straw (MS), wheat straw(WS), biochar of maize (MB) and biochar of wheat (WB) mixed with soil to investigatetheir decomposition characteristics under the same temperature and moisture conditions,with the soil only as control (CK). The results showed that,1) there were no significant difference in soil respiration rate between biochar and CK, while that between biocharand straw was significant. Comparing maize and wheat straw, on average, the biochardecreased soil respiration rate by76%and77%respectively, during the experiment.2)The effect of soil respiration rate and CO₂-C cumulative emission on the straw andbiochar showed similar trend. The biochar of wheat straw and maize straw only released82.43and84.62mg·pot^-1CO₂-C, respectively, but their corresponding straws released355.80and347.00mg·pot^-1,4times more. The percentage of straw carbon transformedinto CO₂-C was55.59%for wheat straw and52.58%for maize straw; these were6times higher than that of biochar.3) Supplying of straw and biochar into soil increasedsoil organic content (SOC) compare with control (CK). After the incubation, the soiltreated with wheat biochar had the highest amount of SOC and was74%higher thanCK. The increase was in order of WB> MB> MS> WS. In conclusion, rate of Cmineralization of wheat and maize biochar is slower than direct straws and stable, andcan increase the soil organic carbon significantly. Supply biochar into soil as anamendment could be an excellent alternative straw management for sustainableagriculture in Guanzhong Plain.3. Based on the fact that biochar application can largely increase the soil organicmatter content in Guanzhong area, we simulated biochar degradation and study itsimpact on soil carbon pool with different application rate in a larger time scale intocalcareous soil. The objective of our experiment was to provide some specificcorrection parameters to the global climate prediction model as well as the detailedtheoretical basis about its application into the fields. Taken the actual situation ofGuanzhong region into consideration, we used5,10,20g/kg soil of maize strawbiochar and wheat straw biochar (WB-5, WB-10, WB-20, and MB-5, MB-10, MB-20),equivalent to the actual amount of11250,22500,45000kg/hm²into the soil. Theresults showed that the biochar mineralization rate fitted perfectly with the logarithmmodel, and this model predicted a controversial situation between biochar degradationrate in100years scale and the initial biochar amount in calcareous soil, the degradationrate followed such order, WB-5> WB-10> WB-20and MB-5> MB-10> MB-20.Biochar application can increase soil total organic carbon content, and there establisheda positive correction. However, there were no significant difference between soilmicrobial biomass C and labile organic carbon content under different biocharapplication rate amounts. From this study, we could conclude that biochar applicationcan increase soil total organic carbon content in calcareous soil in Guanzhong Plain, andthis increase of organic carbon will last at least100years. For a longer existence time of organic carbon, we should input the initial biochar as much as possible.