Study On The Improvement Effects Of Wheat Straw And Biochar On The Tobacco Planting Cinnamon Soil In The Shandong Tobacco Region

At present,the problems of soil organic carbon depletion and soil degradation caused by lack of external organic carbon supplement and excessive application of chemical fertilizer are commonly occurred in tobacco planting area of Shandong Province.A two-year field experiment was carried out to study the effects of conventional fertilization combined with wheat straw incorporation and conventional fertilization combined with different amounts of straw biochar(2.25 t·hm-~2 and 4.5 t·hm-~2)on the physical and chemical properties,soil organic carbon fractions,bacterial community composition,development of tobacco plant,yield and quality of tobacco leaves,aiming to provide theoretical basis and technical support for the rational use of straw to improve the degraded tobacco planting soil.The main conclusions are as follows:1.Crushed straw incorporation significantly increased water-stable macroaggregate content and mean weight diameter by 16.53%and 42.53%,respectively,decreased soil bulk density and the fractal dimension by 14.00%and 5.5%,respectively.In comparison with conventional fertilizer,addition of 2.25t·hm-~2 and 4.5 t·hm-~2 straw biochar only significantly increased MWD by27.76%and 37.5%,respectively.2.Crushed straw incorporation significantly increased contents of alkali hydrolyzed nitrogen and available phosphorus,addition of 4.5t·hm-~2 straw derived biochar significantly increased contents of available phosphorus and available potassium.Continuous incorporation of crushed straw to field significantly increased soil microbial biomass C,hot water extractable carbon,labile organic carbon by 107.0%,252.4%and 68.9%,respectively,and significantly increased soil carbon pool management index by 73.5%,but did not increase the total organic carbon.Biochar addition at application rate of 2.25 t·hm-~2 and 4.5 t·hm-~2 significantly increased the content of soil total organic C,light fraction organic C and microbial biomass C by 74.9%-115.8%,153.5%-326.2%and 37.03%-143.5%,but did not increase soil carbon pool management index.Thus,soil microbial biomass C can make a quick response to SOC changes caused by straw crushing and returning to the field or the addition of biochar.Correlation analysis showed that in comparison with total organic carbon,labile organic carbon fractions,especially microbial biomass C,have a stronger correlation with most soil physical and chemical indicators.3.Crushed straw incorporation and addition of 4.5t·hm-~2 straw biochar significantly increased the number of OTUs and special OTUs,and significantly increased the Chao 1 index,ACE index and Shannon index of soil microorganism,improved the richness and diversity of bacterial communities.However,the effect of biochar at low application rate on bacterial diversity is negligible.Continuous crushed straw incorporation changed the soil bacterial structure and increased soil sucrase,urease and phosphatase activities;the addition of biochar changed the soil bacterial community structure,while had little effect on soil enzyme activity.Soil total organic carbon and available potassium were dominant environmental factors for changes in the bacterial community structure.4.Straw residue at the first year inhibited the growth and development of tobacco plants in the early stage,promoted the growth and development of tobacco plants in the later stage,and increased the yield and quality of tobacco leaves.Consecutive straw incorporation promoted the development of tobacco plants,increased the yield and output value of tobacco,improved the appearance quality,increased the potassium content of middle and upper leaves,but also increased the nicotine content of upper leaves.Biochar addition with different application rate improved characteristics of tobacco plants,increased the yield and output value of tobacco leaves,improved the appearance quality of middle leaves,but increase of the yield,output value and appearance quality scores of tobacco leaves are lower than those in straw incorporation treatments.5.The general scores of soil quality in straw incorporation treatment was higher than that of biochar treatment and conventional control.There was a significant positive correlation between soil quality score and tobacco yield(R~2=0.6298,P<0.01).The correlation between soil carbon pool management index and tobacco yield was poor(R~2=0.2543,P<0.01).The method of principal component analysis is more reliable than the index of soil carbon pool management.In conclusion,the effect of crushed straw incorporation on the improvement of soil quality is more obvious,and it is more conducive to the improvement of tobacco yield and quality.Straw biochar addition is more conducive to the storage of total organic carbon in soil.