Effects Of Maize Straw-Derived Biochars On Organic Carbon Mineralization In An Alkaline Arable Soil

Biochar refers to the solid product obtained by biomass material pyrolysis under high temperature and anoxic conditions.The studies had shown that biochar application to soil plays an important role in soil carbon sequestration and it can reduce carbon emission.Therefore,biomass carbonization and biochar application has become an important way for humans to cope with global climate change.However,the effects of biochar on soil organic carbon mineralization under the condition of without or with nitrogen-fertilizer application is still not clear.In addition,after adding biochar to soil,the role of dissolved organic carbon?DOC?and readily oxidized organic carbon?ROC?in organic carbon mineralization of the incubation system is also deserve to exploration and study.Therefore,this paper made maize straw-derived biochars at different pyrolysis temperatures,analysed the basic physicochemical properties of it.And then,explored the effects of biochars on soil organic carbon mineralization in Loess Plateau alkaline arable soil under the condition of without or with nitrogen-fertilizer application.On the basis of the above research,the maize straw-derived biochars and their carbon skeletons with large differences in active organic carbon components were added to soil to further explore the mechanism of the effects of biochars on soil organic carbon mineralization in Loess Plateau alkaline arable soil under the condition of with nitrogen-fertilizer application.In order to explore the effects of biochar on soil organic carbon mineralization in Loess Plateau alkaline arable soil under the condition of without or with nitrogen-fertilizer application,the maize straw-derived biochar was produced at 400?and 800??respectively designated as BC400 and BC800?.After analyzed the basic physicochemical properties of BC400 and BC800,they were thoroughly mixed with the soil at the mass ratio of 1%and2%.A control treatment?designated as CK?without biochar addition was also arranged.Each treatment was repeated 6 times while 3 of them were carried out with nitrogen-fertilizer application.After 1-week pre-incubation,the indoor static soil incubation experiment was carried out for 50 days.The results showed that:as the pyrolysis temperature increased from 400?to 800?,the pH,C content,the specific surface area and total alkaline oxygen-containing functional group amount of maize straw-derived biochar increased,while the DOC,ROC,N,H,O content decreased,carboxyl and total acidic oxygen-containing functional group amount also decreased.In the treatments without nitrogen-fertilizer addition,compared with CK(5607.71 mg CO₂·kg^-1),biochar application decreased the cumulative CO₂ emission of the incubation system,especially for BC800-1%and BC800-2%treatment(4123.17 mg CO₂·kg^-11 and4375.49 mg CO₂·kg^-1,respectively).Among them,BC400-1%,BC400-2%,BC800-1%and BC800-2%treatments were reduced by 7.65%,0.39%,24.69%and 21.97%,respectively.However,in the treatments with nitrogen-fertilizer addition,compared with CK(4273.55 mg CO₂·kg^-1),biochar application increased the cumulative CO₂ emission of the incubation system,especially for BC400-1%and BC400-2%treatment(5512.13 mg CO₂·kg^-11 and 5659.14 mg CO₂·kg^-1,respectively).Among them,BC400-1%,BC400-2%,BC800-1%and BC800-2%treatment increased by 28.89%,32.42%,2.95%and 3.05%,respectively.Moreover,compared with the biochar application rate,the pyrolysis temperature of biochar had a more significant effect on soil CO₂emission.In the treatments without or with nitrogen-fertilizer addition,maize straw-derived biochar significantly promote nitrification process in soil,especially for BC400-2%treatment.Both the cumulative CO₂ emission and CO₂emission rate showed more significant?P<0.01?relationship with DOC/IN than TOC/IN irrespective of fertilizer addition or not,which indicated that both DOC/IN andTOC/IN were the key factors affecting CO₂ emission in Loess Plateau alkaline arable soil.However,the impact of DOC/IN on soil CO₂emissions was more significant.In order to further explore the effects of maize straw-derived biochars and their carbon skeletons on soil organic carbon mineralization in Loess Plateau alkaline arable soil,the maize straw-derived biochars were produced at 400?,600?and 800?respectively?designated as BC400,BC600 and BC800?.And their carbon skeletons?designated as BS400,BS600,and BS800?were extracted by hot water to remove the active organic carbon.After analyzed the basic physicochemical properties of the six kinds of materials,they were thoroughly mixed with the soil at a mass ratio of 1%and 2%respectively.A control treatment?designated as CK?without biochar addition was also arranged.Each treatment was repeated 3 times.After 1-week pre-incubation,the indoor static soil incubation experiment was carried out for 50 days.The results showed that the pH and the amount of total alkaline oxygen-containing functional group of the biochars and their carbon skeletons significantly increased with the pyrolysis temperature increasing from 400?to 800?,while the contents of dissolved organic carbon?DOC?,readily oxidized organic carbon?ROC?and the amount of total acidic oxygen-containing functional group significantly decreased?P<0.05?.The contents of DOC and ROC of the carbon skeleton were significantly?P<0.05?lower than that of biochar produced at the same pyrolysis temperature.As the pyrolysis temperature of the added materials increased,the cumulative CO₂ emissions of the treatments with biochar or carbon skeleton amendment decreased.Moreover,the cumulative CO₂ emissions of the treatments with biochar amendment were higher than that with carbon skeleton amendment.Especially,the cumulative CO₂ emissions of BC-2%was significantly higher than that of BS-1%?P<0.05?.During the whole incubation,both the contents of DOC and ROC in the amended soil decreased.However,the reduction extent of DOC?87.90%⁸9.18%?was greater than ROC?19.29%³8.49%?.Moreover,both the contents of DOC and ROC showed the following trend:BC-2%>BC-1%/BS-2%>BS-1%>CK during the incubation of the soil amended with 400?,600?or 800?-produced materials.In addition,the study showed that DOC content could explain the variance of CO₂emissions with a higher degree than ROC both in the treatments with biochar and carbon skeleton amendment?P<0.01?.Both DOC and ROC were the key factors affecting CO₂ emissions in Loess Plateau alkaline arable soil.However,the impact of DOC on soil CO₂ emissions was more significant.In summary,under the condition of without nitrogen-fertilizer application,the addition of maize straw-derived biochar inhibited the soil organic carbon mineralization in Loess Plateau alkaline arable soil.However,under the condition of with nitrogen-fertilizer application,the addition of biochar promoted the soil organic carbon mineralization.Compared with the treatment with biochar addition,the effect of carbon sequestration with carbon skeleton addition is better.