| To obtain the characteristics of differences on the biochar yields and basic properties at different pyrolysis temperature and feedstocks,the yields and other chemical properties were determined and analyzed,firstly.At the same time,take black soilsmixed different pyrolysis temperature and feedstocks biochar as the research object,a modified Hedley fractionation and isothermal adsorption equilibrium method were conducted respectively to compare the content of phosphorus fractions,and the adsorption and desorption characteristics of phosphorusin black soils respectively.We purpose to quantify the effects of biochar amendment of different feedstocksand pyrolysis temperature on phosphorus availability in black soils,and obtain an optimum pyrolysis temperature and feedstocksof biochar for improvement on phosphorus availability.On this basis,combined with different freeze-thaw cycles,the adsorption and desorption characteristics of soil phosphorus and the content of phosphorus fractions were measured and analyzed to understand the interaction between freeze-thaw and biochar amendment on the availability of phosphorus in black soil.Different feedstocks and pyrolysis temperatures of biochar affect the yield and chemical properties of biochar.At the pyrolysis temperature of 200? to 700?,the yields of biochar from six feedstocks ranged from 17.35%to 86.97%,and the yields decreased with the increase of pyrolysis temperature.When the pyrolysis temperature was 600?,the yield of biochar from six feedstocks tended to be stable,the yield of rice husk biochar was the highest,and that of soybean straw and soybean pod was the lower.The range of pH value of six biochars was 6.85-8.77,and increased with the raising pyrolysis temperature.The pH value of soybean pods was significantly higher than that of the other five biochars in six pyrolysis temperatures.In addition to rice straw biochar,the total phosphorus content of rice husk,corn straw,corn cob,soybean pod and soybean straw increased with the raising pyrolysis temperature.Under six pyrolysis temperatures,the total phosphorus content of rice husk was the highest,ranging from 1.38 g kg-1 to 2.18 g kg-1,followed by soybean straw and soybean pod.The variation of Olsen phosphorus content in six biochars was differ with temperature,but the Olsen phosphorus content of rice husk biochar was 111.31 mg kg-1 to 360.39 mg kg-1 at 200 C to 700?,which was significantly higher than that of the other five biochars(P<0.05),followed by soybean straw and soybean pod.Biochar amendment of different feedstocks and pyrolysis temperature has influence on the adsorption capacity,adsorption intensity and adsorption ability of soil phosphorus.When the pyrolysis temperature increased to 400?,the adsorption maximum(Qm)of soil treated by soybean pod and soybean straw biochar increased significantly from 855.65 mg kg-1 and 428.84 mg kg-1 to 1666.67 mg kg-1 and 1547.62 mg kg-1,respectively,and then decreased with the further increase of pyrolysis temperature.With the increase of pyrolysis temperature,the adsorption capacity of soil with corn cob biochar increased.The amount of maximum adsorption capacity decreased from 1428.57 mg kg-1 to 556.70 mg kg-1.The change of adsorption constant(KL)and maximum buffer capacity(MBC)was contrary to the adsorption maximum.Soil adsorption constants with soybean pod and soybean straw biochar were 0.0244 L mg-1?0.0529 L·mg-1 and 0.0293 L·mg-1?0.3958 L·mg-1,which first decreased and then increased with the increase of pyrolysis temperature.Soil phosphorus adsorption constant with corn cob biochar was 0.0386 L·mg-1?0.2150 L·mg-1,which increased with the increase of pyrolysis temperature.The amount of phosphorus desorption increased with the increasing phosphorus initial concentration.However,with the increase of pyrolysis temperature,the amount of phosphorus desorption from soil treated with soybean pod and soybean straw biochar increased gradually.With the increase of pyrolysis temperature,he ranges of soil Olsen phosphorus and phosphorus activation coefficients were 41.42 mg kg-1?79.08 mg·kg-1 and 4.49%-7.93%,respectively.In addition to the pyrolysis temperature of 200?,the Olsen phosphorus and phosphorus activation coefficient of soils added with other pyrolysis temperature biochars have increased to a certain extent.The contents of H2O-Pi and NaHCO3-Pi in soil were 5.94 mg kg-1?18.28 mg kg-1 and 46.31 mg kg-1?105.91 mg kg-1,which were similar to Olsen phosphorus and phosphorus activation coefficient.The correlation coefficients of inorganic phosphorus components(H2O-Pi,NaHC03-Pi,NaOH-Pi,HCl-Pi,Residual-P)with Olsen phosphorus in soils were higher significant,which indicated that inorganic phosphorus played an important role in the change of Olsen phosphorus content in biochar-amendedblack soil.Biochar amendment with different feedstocks can change the fixation and release of phosphorus in soil and affects soil availability.After adding different feedstocks biochar to soil,the adsorption maximum of soil ranged from 297.01 mg kg-1 to 2067.09 mg kg-1.The soil adsorption maximum of rice husk,soybean straw and soybean pod was significantly higher than that of corn cob,corn straw and rice straw(P<0.05).Biochar-amended soil phosphorus adsorption constant was 0.0235 L·mg-1?3.2322 L·mg-1,which was negatively correlated with the adsorption maximum,and the correlation coefficient was-0.530.The biochar-amended soil desorption maximum was 309.15 mg kg-1?606.51 mg kg-1,which was negatively correlated with the adsorption constant,indicating that the larger the adsorption capacity of biochar,the easier phosphorus release to the soil.The effects of biochar amendment on soil phosphorus availability were different.The content of Olsen phosphorus and the activation coefficient of phosphorus were 44.95 mg kg-1?305.14 mg kg-1 and 5.28%?16.23%respectively after the biochar applied with different feedstocks.The activation coefficients of available phosphorus and Olsen phosphorus in biochar-amended soils were significantly higher than those without biochar;the contents of phosphorus H2O-Piand NaHCO3-Pi in biochar-amended soils were 8.56 mg kg-1?244.44 mg kg-1,and 44.97 mg kg-1?202.45 mg kg-1,respectively;Except for 300? corn straw biochar-amended soil,the contents of H2O-Piand NaHCO3-Pi in other biochar-amended soils were significantly higher than those in soils.Correlation analysis and path analysis showed that all phosphorus fractions except HCl-P0in biochar-amended soil were significantly correlated with Olsen phosphorus,and H2O-Pi and NaHCO3-Pi contributed the most to available phosphorus.Freeze-thaw cycles effects increases the phosphorus availability of biochar-added soil by increasing phosphorus release from soil.After biochar amendment,the adsorption maximum of the three kinds of soil moisture content decreased from 847.74 mg kg-1?1152.32 mg kg-1 to 817.82 mg kg-1?979.21 mg kg-1,and the change was more significant insoil moisture contents of 22%and 45%of biochar added soil.With the increasing frequency of freeze-thaw cycles,the average desorption ratio of phosphorus increased from 15.98%at 0 freeze-thaw cycles to 17.09%after 12 freeze-thaw cycles in biochar-amended soil with 22%moisture content.The average desorption ratio of phosphorus increased from 15.93%at 0 freeze-thaw cycles to 17.44%after 12 freeze-thaw cycles in biochar-amended soil with 45%moisture content,means the effect of freeze-thaw cycles on phosphorus availability was more obvious in biochar-amended soil with higher moisture content.With the increasing frequency of freeze-thaw cycles,the soil labile phosphorus showed an increasing trend in biochar-amend higher moisture content soil.The soil labile phosphorus increased to 6.90%after 12 freeze-thaw cycles.Due to the direct action of NaOH-P0,biochar can improve the soil phosphorus availability after freeze-thaw cycles.Principal Component Analysis(PCA)showed that the soil moisture content was the main driving factor for the change of phosphorus fractions in biochar-amended black soil. |
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