Effects Of Tillage And Fertilization On Anammox And Denitrification Rates In Paddy Soils

The nitrogen use efficiency of paddy soil was only half of that of upland,and the utilization rate of nitrogen fertilizer in paddy soil was only 28.3%.Various biochemical processes can occur regarding nitrogen cycle in paddy soils.Ammonia volatilization,nitrate leaching and denitrification,result in substantial N loss,yet a large proportion of N losse in unknown ways.Anaerobic ammonia oxidation?anammox?,a significant breakthrough in the field of N cycle in the new century may contributes to this unaccounted N loss.The presence and the contribution of anaerobic ammonia oxidation to N₂ loss in paddy soil are still unclear.The purpose of this study was to quest the existence of anammox in purple paddy soil and its contribution to N₂ loss in paddy soils under different tillage and different fertilization modes,and their denitrification rates.The soil samples were collected from the purple soil long-term experimental base of Southwestern University in Beibei,Chongqing.Eight neutral purple paddy soils were selected as experimental material including three soils under different tillage modes and five under different fertilization modes.Determination of denitrification rate and anaerobic ammonium oxidation rate in different paddy soils by15 N isotope tracer technique.Determination of denitrification potential and N₂ O emission rate of 3 paddy soils with different tillage models were assessed by acetylene inhibition method.The main results are shown in the following part:?1?Effects of different tillage patterns on denitrification potential and N₂ O emission rateAfter 50 or 100 mg N kg^-1dry soils NO₃-were added,NO₃-content in combining ridge with no-tillage paddy soils?LZ?decreased most rapidly,significantly higher thanthat of flooded paddy field?DS?and conventional paddy-upland rotation?CG??p<0.01?.Flasks with acetylene added,N₂0 content in LZ increased most rapidly,significantly higher than that of DS and CG(p<0.05.Selected the period from 12 h to 24 h when NO₃-was excess,to characterizate the denitrification potential and N₂ O emission rate.The order of denitrification potential of three paddy soils under different tillage modles were:LZ(4.93 + 0.55 mg N kg^-1 h-1)> DS(4.10 + 0.07 mg N kg^-1 h-1)> CG(2.40 + 0.14 mg N kg^-1 h-1),the difference was significant?p<0.05?.The N₂ O emission rate of LZ and DS were significantly higher than that of CG?p<0.05?,difference between LZ and DS was not significant.?2?Effects of tillage and fertilization patterns on denitrification rate in Paddy SoilsThe denitrification rate of different tillage paddy soil ranged from 2.85 to 4.20 nmol N g-1 h-1,while the denitrification rates in DS and LZ were significantly higher than that of CG?p<0.05?.As far the paddy soils under different fertilization modes,the denitrification rates were between 1.58⁴.00 nmol N g-1 h-1.The denitrification rate of no fertilizer input paddy soil?CK?was significantly lower than that of fertilized soils,while highest denitrification rates were found in soils with organic and inorganic fertilizer input?BS and ZL?.Denitrification rate was significantly correlated with soil organic carbon,total nitrogen and C/N?r=0.762?.?3?Effects of tillage and fertilization modes on anaerobic ammonium oxidation rate in Paddy SoilsAnaerobic ammonium oxidation occurred in paddy soils under different tillage and fertilization models.Anaerobic ammonia oxidation rates of DS and LZ paddy soils were1.09 + 0.18 nmol N g-1 h-1 and 0.82 + 0.33 nmol N g-1 h-1 respectively,significantly higher than that of CG?0.42 + 0.10 nmol N g-1 h-1??p<0.05?.The anaerobic ammonium oxidation rate of paddy soils under different fertilization patterns varied from 0.22-0.53 nmol N g-1 h-1,which increased with the increase of fertilizer application intension approximately.There was an extreme significant positive correlation between anammox activity and C/N,soil organic carbon?p<0.01?,while significantly correlated with soil total nitrogen?p<0.05?.The contribution of anaerobic ammonia oxidation to N₂ production was8.56²0.62%.In terms of paddy soils with different tillage patterns,the contribution of anaerobic ammonium oxidation to N₂ production was higher than that of paddy soils with different fertilization patterns.With the increase of fertilization intensity,the contribution of anaerobic ammonium oxidation to N₂ yield was higher.In this paper,isotope-pairing technique was used to measure the denitrification and anammox rates of different purple paddy soils.The denitrification potential and N₂ O emission rate of paddy soils with different tillage patterns were studied by indoor culture method.The main conclusions are as follows:?1?Denitrification potential of combining ridge with no-tillage paddy soil?LZ?was significantly higher than that of flooded paddy field?DS?and conventional paddy-upland rotation?CG?;?2?The anaerobic oxidation of ammonium?anammox?process has been observed in paddy soils with different tillage and fertilization pattens,suggesting anaerobic ammonia oxidation is an important way of N loss in paddy ecosystem;?3?The greater the intensity of fertilization was,anaerobic ammonia oxidation activity was higher.Anaerobic ammonia oxidation contributed to 18.65–20.62% N₂ production in LZ and DS,higher than the other paddy soils.The nitrogen cycling and N₂ balance need to be reevaluated in paddy ecosystem.