Effects Of Biochar On Acidity And Nitrogen Transformation And Related Response Mechanism Of Microbial In Soils With Different Tea Cultivation Years

Soil acidification is becoming worse in tea garden as long-term overuse of nitrogen fertilizer and metabolism of tea tree under many tea cultivation years.This change produces great impact on yield and quality of tea production.Meanwhile,nitrogen leaching caused by excessive nitrogen fertilizer and its unbalanced application in tea gardens are also the main reasons for non-point source pollution and eutrophication in the surrounding water bodys of tea gardens.To achieve the win-win goal for the improvement of tea yield and quality and the protection of water quality,seeking economic and effective measures to improve soil acidification,ehance nitrogen utilization rate of tea tree and reduce nitrogen loss has become a hot topic in the research of tea garden production and non-point source pollution control.As an environmentally friendly material with special physical and chemical properties,biochar has been shown to be a promising application prospect in reducing soil nutrient loss,improving soil quality and increasing crop yield.Based on pot experiment in unheated greenhouse,biochar?application rate:3%and 6%?was added to two soils with different tea cultivation years?20 years and 60 years?.The main findings are listed as follows:?1?The biochar addition significantly increased soil p H but decreased the total amount of exchangeable acid,exchangeable H⁺and exchangeable Al³⁺in both soils.Furthermore,the more biochar was added,the greater effect was on the acidity of tea soil.For the treatment with 6%of biochar application,compared with no biochar addition,the soil p H increased by 1.06-1.10 and 0.75-0.99 units and the exchangeable Al³⁺content decreased by 50.7-61.3%and 49.4-67.2%in soil with 20 years and 60years of tea planting,respectively.These results indicates that biochar addition can improve soil acidification and reduce the toxic effect of aluminum on crops in tea garden effectively.?2?The biochar addition reduced the leaching losses of NH₄⁺-N,NO₃^--N and total nitrogen?TN?by 26.5-91.9%,32.6-69.2%and 38.7-72.2%,respectively.The greater the amount of biochar addition,the greater the reduction in leaching nitrogen.The results of leaching experiment show that inorganic nitrogen was the main form of nitrogen leaching from tea garden soil,accounting for 66.4-74.1%of the total cumulative nitrogen leaching,and the concentration of NO₃^--N in the leaching solution was significantly greater than the concentration of NH₄⁺-N.Compared with the soil with 20 years of planting tea,biochar had a better effect on reducing TN leaching in soil with 60 years of planting tea.?3?The biochar addition increased the soil total nitrogen content in both soils,which was beneficial to soil nitrogen sequestration.Based on the ¹⁵N labeled urea,the resulst exhibited that the proportion of fertilizer nitrogen to leaching loss,soil residue,plant absorption and gaseous loss were 14.6-47.9%,30.7-48.5%,2.25-4.91%,and13.9-38.9%.The biochar addition reduced the leaching loss of fertilizer nitrogen and increased the residual amount of fertilizer nitrogen in the soil,but also enhanced the proportion of fertilizer nitrogen lost in gaseous form.?4?The biochar increased the activities of urease,N-acetyl-?-D-glucosidase,and nitrite reductase in both soils.The 3%biochar addition significantly increased the?-glucosidase activity in both soils.While the 6%biochar addition reduced the?-glucosidase activity in soil with 20 years planting to a certain extent,but increased it in soil with 60 years planting.?5?The Chao and Shannon index in soil with 20 years planting were higher than in soil with 60 years planting.The biochar application significantly increased the Chao index and Shannon index in soil with 60 years planting.The dominant bacteria in the tea garden soil were Proteobacteria,Acidobacteria,Actinomyces,Pachyphyta,and Campylobacter.The redundant analysis results showed that soil urease activity,total nitrogen content,microbial biomass carbon,nitrite reductase activity,and p H were closely related to the soil bacterial community in the tea plantation.