Effects Of Successive Application Ofcrop-straw Biochar On Soil Fertility, Carbon Sequestration And Greenhouse Gas Emission In Cambosols

Annually about 0.6⁰.7 billion tons of crop straw is produced in China whereby less than half failed reasonable use that cause a series of problems such as resource waste and environmental pollution. Biochar, a pyrolyzed biomass with its high carbon concentration and stabilize C sink can improve soil carbon pool rapidly when return to soil. Converted by crop-straw, crop-straw biochar returned into soil not only increase carbon sequestration and reduce emission of greenhouse gases as well as soil quality conservation, but also provides effective ways for comprehensive utilization of straw resource diversity. In order to evaluate the beneficial effect of biochar, a three-year field experiment（6 seasons of 3 each wheat and maize crop rotation） was conducted with successive crop-straw biochar application on cambosols（p H 8.30） in North China Plain. Biochar was applied at the rate of 0（BC0; control, CK）, 2.25 t hm-2（BC2.25; low level）, 6.75 t hm-2（BC6.75; medium level） and 11.25 t hm-2（BC11.25; high level）. Biochar treatments were applied successively to both crops each season. The experiments were set up in randomized complete block design（RCBD） on plot size of 16 m2 replicated three times. Data on crop yield, grain quality, crop uptake, soil fertility, carbon sequestration and N₂O emission were recorded. Results showed that:（1） Total aboveground biomass yield over 6 seasons increased as affected by successive biochar application: the straw yield and above-ground biomass yield ware increased by 7.18% and 5.30% with BC11.25 treatment compared with BC0 treatment, nevertheless, grain yield were no significant influence with biochar application. Biochar has no negative effects on grain property such protein, grain bulk weight and wet gluten content.（2） The uptake of N and K in total above-ground biomass was increased with biochar application rate increaded, but there is no significant difference; another nutrient such as P, Ca, Na, Mg, Fe, Mn, Cu and Zn were no increasing trend with biochar application. Biochar application can significant improve soil available nutrient, such available P was significant increased by 36.11% in the 6th season with BC11.25 treatment, available K content was improved from the 2nd season and increased by 308.48⁴78.27% with BC6.75 and BC11.25 treatment in the 6th season, respectively; available Na content also improved with biochar application; moreover under BC6.75 and BC11.25 treatment available Mn and Zn content also increased by 21.30³4.99% and 69.66¹17.37% in the 6th season, respectively.（3） Soil total nitrogen was improved slowly and in the first 4 season there was no significant difference until TN was increased by 23.09% with BC113 treatment in the 5th season; in the 6th season TN was enhanced by 19.54% and 25.01% with BC6.75 and BC11.25, respectively. Total organic carbon（TOC） in soil was enhanced with medium and high level biochar application in the 3rd season, till last crop season TOC was significant increased to 8.56¹7.81 g kg-1 and by 28.27¹66.93%.The increased of TOC lead to the C/N ratio enhanced: after 6 crop seasons the C/N ratio was enhanced from 8.21 in BC0 treatment to 9.88, 13.85 and 17.48 with BC2.25, BC6.75 and BC11.25 treatment, respectively. But the dissolved organic carbon（DOC） was with no significant difference. The rough estimate with the substraction method showed that the biochar superficial decomaosition rate was in 8.94⁹.80% annually. biochar application has no significant effluence on NO3--N in the first 5 crop seasons but in the last season NO3--N wan enhanced by 25.31% with BC11.25 treatment, but the NH4+-N was no affected by biochar application.（4） With the high water holding capacity（WHC） of biochar, soil WHC was increased by 19.57% and 27.78% in 6th crop season with medium and high level biochar application, and soil average moisture content was enhanced with biochar application from the 3rd crop season with BC11.25 treatment and till the 6th crop season was enhanced by 8.15%, 18.59% and 29.83% with biochar application. In addition, soil saturated hydraulic conductivity was significant affected by biochar application, in the 6th season the saturated hydraulic conductivity was increased by 112.20% and 390.8% with medium and high level biochar addition. Moreover in the last crop seasons the cation exchange capacity（CEC） was affected by biochar application, under BC6.75 and BC11.25 treatment CEC was enhanced by 7.99⁸.16% with BC11.25 treatment. Soil bulk density was reduced from the 2nd crop season, till the last season soil bulk density was decreased by 12.67% and 7.97% with BC6.75 and BC11.25 treatment. However the p H value of soil was no affected by biochar over the 6 crop seasons except 2nd season in spite of high p H value of biochar（10.5）.（5） Biochar has no effect on N₂O emission until the 5th season, accumulation emission of N₂O was reduced by 48.12% and 51.99% and yield scared reduced by 50.65% and 51.26% with medium and high level biochar application in the last season, respectively. Over the 6 season the total N₂O was reduced by 38.24% with BC11.25 treatment, and yield scared N₂O emission was reduced by 31.49⁴0.21% with biochar application.All the findings suggest that successive application of crop straw derived biochar have positive effects on crop growth which main reflected in straw yield increased; although there was no positive on grain yield, no negative influence on grain quality occurred. Biochar application could increase soil fertility such as soil available P, K, Na, Mn and Zn increased gradually; soil physical property such as moisture content, WHC, saturated hydraulic conductivity and posrosity were increased. Moreover the stability of soil carbon pool was increased and N₂O emission was reuced. Therefore biochar application has positive effect on soil fertility improved, carbon sequestration and greengas emission reducd in the cambosols in North China. This paper is a report for stage work for long term experiment of successive biochar application in North China Plain, there were much question need to be resolved. We will insist in the field experienceand do some further in-depth studies on effect of long-term biochar application on soil water and nutrient dynamic and some other physico-chemical properties of cambosols and nutrient translocation in plant as well as carbon sequestration and greenhouse emission, explore the threshold of the rate of biochar before the yield decreased, and confirm the potential of biochar application on soil property and carbon sequestration when reach to the threshold, in the hope that the study may provide some scientific data to support extrapolation of the application of crop straw derived biochar in upland of North China.