Effect Of Application Of Straw-derived Biochar On Denitrification And Anammox In Paddy Soil

Due to the long-term flooding environment in the paddy field,denitrification has become the main way of nitrogen loss in the paddy field,however the anammox process has also led to the loss of nitrogen in the paddy field.Because the end products of the two processes are both N₂,they are collectively called denitrogenation.Every year in our country can produce a large number of crop straw.Under the condition of hypoxia,the straw can be decomposed into biomass charcoal at high temperature,which is a winning way to realize the effective utilization of resources,the improvement of soil fertility,and the carbon sequestration and emission reduction.Application of biochar can alter denitrification and anammox process in the paddy field by changing physicochemical and microbiological properties of the paddy soil.This paper selects farmland soil in the Taihu Lake Basin,through 2 years of indoor and outdoor observation experiments,The surface soil and profile leakage water solution of rice fields were collected,and the use helium confined culture technology,membrane inlet mass spectronmeter and gas chromatography to study the addition of straw-derived biochar for many years(CK:each season 0 t ha^-1;1BC:each season 2.25 t ha^-1;5BC:each season 11.3 t ha^-1;10BC:each season 22.5 t ha^-1).The denitrification potential and anammox potential of the soil surface under different treatments,and the concentration of N₂O and ex N₂in the soil profile under0-1 m temporal and spatial distribution characteristics and influencing factors.The main conclusions are as follows:1.The denitrification potential range of each treatment in the surface soil during 2years is between?0.78±0.05?-?1.49±0.32?nmol Ng^-1h^-1,and the anammox potential range is?0.13±0.05?-?0.50±0.07?nmol Ng^-1h^-1,where denitrification potential and anammox potential account for?73.71±3.51?%-?85.63±1.27?%and?14.36±4.14?%-?26.28±3.51?%of the total nitrogen production,respectively.The denitrification potential of each treatment is much greater than anammox,and the contribution rate to nitrogen removal is also greater than anammox,indicating that the denitrogenation activities in paddy soil are dominated by denitrification activities.Therefore,the main source of N₂in rice fields is denitrification.2.Compared with CK,After adding biochar,the total denitrogenation potential of the surface soil was reduced in 1BC?5BC and 10BC for 2 years,and the denitrification potential decreased the most in 5BC and 10BC,indicating that the straw-derived biochar mainly reduced the denitrification effect,thereby reducing the total denitrogenation potential of the surface soil.3.The concentration of N₂O is higher in the soil 60 cm in depth in CK and ex N₂concentration decreased with soil depth in soil profile solution.N₂O and ex N₂concentrations in profile decreased with rising biochar application rate,thus being the lowest in treatment 10BC.Among them N₂O concentration decreased the most significantly in the soil 60 cm in depth and ex N₂concentration decreased with increasing soil depth.Biochar amendments had no obvious effect on inorganic nitrogen?NO₃^-+NH₄⁺?in the soil profile,but increased the concentrations of soluble organic carbon?DOC?,dissolved oxygen?DO?and redox potential?Eh?in 5BC and10BC.The variations of N₂O and ex N₂was related to DOC,NO₃^-and DO in CK,and to DO and Eh in the biochar treatments.4.The leaching amount of ex N₂?calculated by 1 m depth?is 2.3-5.5 kg ha^-1in CK,which was equivalent to 32%-34%of the leaching amount of inorganic nitrogen and organic nitrogen?DON?,while it was reduced to 1.7-3.7 kg ha^-1and 1.1-1.9 kg ha^-1in 5BC and 10BC.All the findings show that the leaching amount of N₂produced by denitrification with water can not be ignored,the amendment of biochar can improve aeration of the soil profile and increase DO and Eh,thus inhibiting denitrification and reducing the risk of leaching loss of its main gaseous products,ex N₂.