| Biochar,which is produced by the pyrolysis and carbonization of biomass?such as crop straw?under complete or partial anoxic conditions,has a rich carbon content,developed pore structure,stable nature,and high aromatization.Returning biochar to farmland can not only realize efficient utilization of waste biomass resources,but also improve soil.As the most widely distributed cultivated soil in the lower reaches of China's Huaihe river and Loess Plateau,tillage loess has many shortcomings,some of which include:poor water retention,low organic matter content,poor structure,as well as poor nutrient and fertilizer retention.Sulfur is an essential nutrient for plant growth and development.In recent years,with the increase of agricultural production and the extensive use of sulfur-free fertilizers,the content of sulfur in soil has decreased.This has led to an increase of sulfur deficiency in plants.Soil sulfur deficiency has become a new problem affecting agricultural production.At present,there are many studies on the effects of biochar on nitrogen and phosphorus in soil,however there are few studies regarding biochar's effects on the transformation of sulfur in soil.Biochar pyrolyzed at 300°C and 600°C?BC300 and BC600?was applied at applications rates of 0%,1%,3%,and 5%to loess.The treatments were incubated at a constant temperature for 15 weeks in order to study the effects biochar had on the physicochemical properties,sulfur transformation,and microbial community structure of loess.Samples were taken at 0,3,6,9,12,and 15 weeks in order to determine the physicochemical properties and the content of various forms of sulfur in the soil.The effects biochar application had on the physicochemical properties of tillage loess and the conversion of various forms of sulfur in soil were studied.After 15 weeks of incubation,16S rDNA amplicon sequencing technology was used to perform high-throughput sequencing of soil samples to study the effects of biochar application on OTU abundance,microbial diversity,species composition,and the dominant flora distribution of soil microbes.This study provides a theoretical reference for the improvement of tillage loess and tillage loess fertilizer?sulfur fertilizer?with biochar.The main findings are as follows:?1?The effect of biochar on tillage loess properties is related to the incubation time and the pyrolysis temperature and application amount of biochar.The application of biochar from corn straw into loess can improve soil pH value,EC value,organic matter content,urease and catalase activity.The higher the application of BC300 and BC600,the higher the soil pH value,EC value and organic matter content.After incubation for 15 weeks,soil pH values were 5.70,5.86,5.94 and 6.01 when BC300 was applied at 0%,1%,3%and 5%,respectively.The conductivity EC values were 0.6,0.73,0.93 and 1.12 ms·cm-1,respectively.The content of organic matter was 1.96%,2.34%,2.64%and 2.57%,respectively.When the dosage of BC600 was 0%,1%,3%and 5%,the pH values of soil were 5.70,5.90,5.96 and 6.07,respectively.The conductivity EC values were 0.6,0.91,1.0 and 1.15 ms·cm-1,respectively.The content of organic matter was 1.96%,2.16%,2.40%and 2.52%,respectively.The effect of BC300 and BC600 on soil urease and catalase activity changed with the change of incubation time.At week 9,BC300 and BC600 showed the most significant increase in soil urease and catalase activity.In addition,the increase of soil pH value and urease activity by BC600 was more obvious than that by BC300,and the increase of soil organic matter content by BC300 was more obvious than that by BC600.The effect of 3%BC300 and 5%BC600 on the improvement of catalase in soil was the strongest,respectively.?2?The content of various forms of sulfur in tillage loess changed with the passage of cultivation time,and the influence of different pyrolysis temperature and amount of biochar on the content of various forms of sulfur in soil was different.The total sulfur content in soil decreased after BC300 and BC600 were applied.At week 15 of incubation,when the application amount of BC300 was 0%,1%,3%and 5%,the total soil sulfur content was728.12,692.00,707.59 and 686.14 mg·kg-1,respectively.When the amount of BC600 was1%,3%and 5%,the total sulfur content in soil was 654.90,680.50 and 631.89 mg·kg-1,respectively.When BC300 and BC600 were applied,the content of water-soluble sulfur in soil increased,and when the amount of BC600 was 1%,the increase of water-soluble sulfur in soil was the largest.At the initial stage of cultivation,both BC300 and BC600 could increase the adsorbed sulfur content in the soil,and when the amount was 3%,the increase of adsorbed sulfur in the soil reached the maximum.When the amount of BC300 was 1%and 3%,the soluble sulfur content of hydrochloric acid in soil could be significantly increased.When the amount of BC600 was 3%,the soluble sulfur content of hydrochloric acid in soil was increased most significantly.According to the change of inorganic sulfur content in soil,application of BC600 can facilitate the transformation of water-soluble sulfur in soil to adsorbed sulfur and soluble sulfur in hydrochloric acid.The content of organic sulfur in soil decreased after BC300 and BC600 were applied.At week 15 of incubation,when the application amount of BC300 was 0%,1%,3%and 5%,the total soil sulfur content was286.55,257.51,262.26 and 251.0 mg·kg-1,respectively.When the amount of BC600 was 1%,3%and 5%,the content of total sulfur in soil was 200.32,249.53 and 177.75 mg·kg-1,respectively.The decrease of total sulfur content in soil is attributed to the decrease of organic sulfur content in soil.When the amount of BC600 is 5%,the decrease of organic sulfur reaches the maximum.?3?After the application of BC600,the number of unique OTUs in soil samples increased.Higher application rates of BC600 also led to an increased amount of unique OTUs.The application of BC300 at 1%and 3%,as well as the application of BC600 at 5%was seen to reduce the number of microbial communities in the soil.The application of BC600 at 1%and 3%saw increases in the number of microbial communities.After the application of BC300 and BC600,the relative abundance of Proteobacteria increased and the relative abundance of Gemmatimonadetes decreased.As biochar application rates increased,the relative abundance of Actinobacteria and Planctomycetes increased.However,the relative abundance of Bacteroidetes,Acidobacteria,and Verrucomicrobia decreased with higher application rates.The relative abundance of Chloroflexi and Euryarchaeota increased as application rate of biochar increased.After application of BC300 and BC600,the microbial community diversity in the soil increased.When biochar was applied at 3%,the microbial community diversity in the soil was the highest.When biochar application rates were lower,the community richness of microorganisms in the soil was increased.After application of biochar,the distribution of species tended to be more uniform.Out of all the biochar treatments,the application of BC600-3 was seen to improve soil bacterial richness the most.The effect of BC600 on soil species composition was greater than that of BC300.Higher biochar application rates led to a greater impact on the microbial species composition in the soil. |
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