Study On The Effect Of Wheat Straw Biochar On Soil Improvement

Biochar is a solid particulate matter with high content of carbon and stable physicochemical properties,which formed through high-temperature cracking under anaerobic or oxygen-limited conditions.It is widely used for soil improvement because of its excellent characteristics such as high p H,abundant pore structure and surface functional groups.At present,the soil quality of agricultural land in arid areas of China continues to decline due to climate,precipitation and over-fertilization,and problems such as soil consolidation,water and fertilizer loss keep arising.Based on it,this study selected the gray desert soil in Xinjiang and the aeolian soil in Shanxi Province as the research objects,and used wheat straw biochar as the soil amendment.In this study,the laboratory simulation test was used,and biochar at 0%,0.5%,1.0%,2.0%,4.0%and 8.0%of soil quality was added at once.We collected soil samples at weeks 0,1,2,3,5,7,9,12 and 36,and measured the soil chemical properties and soil microbial biomass carbon and nitrogen.Four common soil enzymes that sensitive to biochar were selected.The changes in enzyme activities were observed,and the mechanism change were explored by enzyme kinetics.The main conclusions are as follows:（1）The morphological and structural characterization of biochar revealed that wheat straw char has a rough surface with abundant pore structure and large specific surface area,and carbonyl（C=O）,hydroxyl（-OH）,aliphatic ether（C-O-C）,aromatic ether（Ar-O-R）,aromatic C-N bond and C=C bond groups are mainly present on the surface.（2）The addition of biochar significantly increased the p H,increased the content of available phosphorus,ammonium nitrogen and soluble organic carbon in soil,and significantly decreased the content of nitrate-nitrogen in the gray desert soil and the aeolian soil,and the application of biochar was significantly correlated with the p H value,available phosphorus and nitrate-nitrogen content（p<0.05）.Between the two soil types,all indicators were higher in the gray desert soil than aeolian soil,except for the available phosphorus content,which was lower than that in the aeolian soil.Further study found that the application of biochar greatly affected the soil nitrogen cycle,including the accumulation of soil mineral nitrogen decreased,net mineralization rate and net nitrification rate significantly decreased,soil nitrification and mineralization had a significant inhibition effect,indicating that the application of wheat straw biochar promoted the assimilation of nitrogen by soil microorganisms.（3）The application of biochar in the gray desert soil and the aeolian soil significantly increased soil microbial biomass carbon content,both with the greatest increase under 4.0%biochar treatment.Biochar could promote soil microbial biomass nitrogen in a certain extent,but when the application amount of biochar was higher,the soil microbial biomass nitrogen decreased,even lower than that of in the control.The changes in soil microbial biomass carbon were consistent with the increase in the incubation time,both of which increased first and then decreased,and the greatest increases were observed at the 3rd and 5th weeks,respectively.The changes of soil microbial biomass nitrogen were inconsistent.The MBN in the gray desert soils showing a trend of increasing and then decreasing,and the aeolian soils showing a trend of first increasing and then slowly decreasing and then increasing.The carbon and nitrogen ratio of soil microbial biomass was significantly higher in biochar application level（8.0%）than the other treatments,indicating that a certain level of biochar application may increase the stability of the soil environment.（4）The activities of soil urease,alkaline phosphatase and sucrase were significantly increased by the addition of biochar,and catalase was promoted mainly in the later stage.However,when the addition of biochar was high,soil enzyme activity was slightly inhibited.The total enzyme index（TEI）of the soil was found to be greatest at 4.0%biochar addition for the two soil types,and the TEI in the grey desert soil was higher than that in the aeolian soil for all treatments.Redundancy analysis showed that soil enzyme activity was influenced by soil available nutrients and microbial biomass,of which NO₃^--N,MBC,AP,DOC,and MBC/MB were the main factors,and the ranking of each influencing factor for the two soils were NO₃^--N>MBC>AP>DOC>MBC/MBN and MBC>NO₃^--N>AP>DOC>MBC/MBN.（5）The addition of biochar had a significant effect on soil enzyme kinetic parameters.After biochar addition,V_max and V_max/K_m of four soil enzymes was increased,while K_m varied inconsistently,with increased K_m for urease,alkaline phosphatase and sucrase,and decreased K_m for catalase.The addition of biochar increased the catalytic capacity of soil enzymes,but the effect on their affinity with substrates was related to different factors,indicating the complexity of the action between biochar and soil enzymes,which may also be related to the function of soil enzymes.The soil enzyme kinetics parameters V_max and V_max/K_m showed a trend of continuous increase or increase followed by decrease with increasing biochar application,while there was no consistent pattern in the response of K_m to biochar.The response of K_m to biochar showed no consistent pattern and fluctuated with the increase of biochar application.In addition,the enzyme kinetic parameters changes in incubation time and soil type was depending on the enzyme species.The redundancy analysis showed that soil enzyme kinetic parameters were influenced by soil biochemical factors,among which soil p H,AP,NH₄⁺-N,NO₃^--N,DOC,MBC,MBN and MBC/MBN had significant effects on soil enzyme kinetic characteristics.In conclusion,by studying different types of soil chemical properties and soil microbial biomass carbon and nitrogen response to the applying biochar and its content,observation of enzyme activity and kinetic parameters with the change of applying biochar content,combined with the economic benefit of agricultural production,4.0%biochar seems best effect to the promotion of two kinds of soil quality.