Effects Of Long-term Application Of Biochar On Soil Carbon Pool

An increasing interest in soil carbon sequestration induced by biochar due to its contribution on enhancing soil organic carbon stocks and consequent relieving the increasing trend of atomospheric CO₂concentration is emphasized.Previous,the conclusions of effect of biochar application on soil carbon pool mainly based on short-term incubation or field experiment,but the long-term effects of biochar on soil carbon is still limited.On the one hand,this study based on a 10-yr field experiment of biochar application included three treatments:no biochar amendment?Control?,biochar application at 4.5 t ha^-1yr^-1?B4.5?and 9.0 t ha^-1 yr^-1?B9.0?.The air-dry soil samples sieved through a 2–mm sieve were collected from 0–7.5 cm and 7.5–15 cm soil depths and then fractionated into>250?m,53–250?m,2–53?m,<2?m different particle-size fractions by combing physical with chemical fractionated method.This study analyzed SOC contents and stocks of bulk soil and fractions and soil inorganic carbon?SIC?,as well as combined soil moisture,pH,cation exchange capability?CEC?and microbe biomass carbon?MBC?to discuss the mechanisms of biochar effects.Hereafter,sampling soil samples from 0–7.5 cm,7.5–15 cm,15–30 cm,30–60 cm and 60–100 cm depths,which were prepared to determine the total soil organic carbon?TOC?and dissolved organic carbon?DOC?contents among soil profile.On the other hand,in order to clear the effect of biochar addition on the mineralization and release on native SOC under an incubation experiment?CK:no biochar amendment;B5:5%biochar?using the different isotope characteristic values of native woodland soil?C3,–26.4‰?and maize biochar?C4,–12.6‰?to distinct and magnitude carbon from soil or biochar was carried out in this study.The main conclusions are as follows:?1?For the surface soil in the field?0–7.5 cm and 7.5–15 cm?,compared with the control treatment,SIC content under B4.5 and B9.0 treatments enhanced by 3.3%–19.5%,coarse particulate organic carbon?cPOC?,fine particulate organic carbon?fPOC?,intra-microaggregate organic carbon?iPOC?fractions and the bulk soil organic carbon?SOC?increased by 18.4%–292.8%,28.6%–150.1%,65.2%–107.3%,15.7%–87.1%,respectively,whereas soil silt-clay associated organic carbon?SCOC?decresed by 2.0%–28.4%.SOC,SIC and total carbon?TC?stocks enhanced by 0.6%–6.5%,19.9%–53.5%,14.5%–43.1%,respectively.?2?For the 0–100 cm soil depth,TOC contents significantly increased after biochar application among soil profile?2.4%–109.9%?.DOC contents increased by?25.3%–75.8%?among 0–15 cm soil profile,DOC contents decreased by 3.9%–54.2%among 15–100 cm soil profile.?3?The incubation results showed that cumulative CO₂ emission under B5 treatment increased but,the released magnitude and mineralization of native SOC was significantly decreased and depressed,compared with the no-biochar control,showing as negative priming effect?–11.8%?.Our located field experiment results showed that long-term biochar application significantly increased SIC,SOC and TC contents and stocks in surface soil,suggesting obvious soil sequestration.The accumulation of SIC partly contribute to the C sequestration of biocahr,and biochar particles mainly riched in large particle-size fraction.Biochar may have a positive priming effect on the native SOC due to the decreasing of relative small-size fraction.Incubation results showed a negative priming,suggesting that incubation experiment may underestimate the actual magnitude of priming effect of biochar under field.