Paddy Soil Nitrification And Denitrification Potential And Its Relationship With Iron And Manganese In Major Rice Producing Areas Of Hubei Province

Agricultural soil nitrification and denitrification proceses,causing significant nitrogen loss and the greenhouse gas N2 O emission,have become hot research issues in recent years.The biogeochemistry cycles of iron and manganese have received much attention,due to their extremely lively variable valences and important roles in soil nitrogen transformation and associated N2 O emission under the circumstance of complicated changeable oxidation-deoxidization conditions in the paddy soil.In the present study,24 contrasting paddy soils were sampled from the major rice producing areas of Hubei Province(4 soil samples in Xianning City: X1,X2,X3,X4;4 soil samples in East and West Lake areas of Wuhan City: W1,W2,W3,W4;2 soil samples in Tianmen City: T1,T2;1 soil sample in Zhijiang City: Z;5 soil samples in Ezhou City: E1,E2,E3,E4,E5;5 soil samples in Qianjiang city: Q1,Q2,Q3,Q4,Q5;3 soil samples in the campus test field of Huazhong Agricultural University: H1,H2,H3)to investigate soil nitrification and denitrification potentials,analyzed the differences in nitrification and denitrification potentials between different soils,and discussed the coupling relationship between the soil nitrification and denitrification potentials and the soil iron,manganese contents as well as other influencing factors(soil pH value,texture,soluble organic carbon,organic matter,total nitrogen and inorganic nitrogen).This study could improve our understanding of the mechanisms underlying soil nitrogen transformation and its relationship with iron and manganese contents and forms,providing theoretical basis knowledge for paddy soil nitrogen use efficiency research in the Middle-lower Yangtze Plain.The main conclusions of this study are as follows:(1)There existed significant differences in nitrification potentials between the 24 sampled paddy soils,ranging from 0.11 to 17.22 mg N kg-1 d-1.Among all the tested soils,the higher the soil pH value and lighter the soil texture,the higher the nitrification potential is(T1,T2,Q1,Q2,Q3,Q4,Q5),while the lower the soil pH value,the lower the nitrification potential is(X2,X3,X4,E3,E4,E5,H1),except for some soil samples(W2,W3,W4)with relatively high nitrification potentials with pH values below 7.(2)There existed significantly positive correlation between the soil nitrificationpotential and the content of amorphous iron in the soil(p< 0.05).The increase of amorphous iron content was conducive to the process of soil nitrification.When the pH value was less than 6.5 in the soil,the amorphous iron content had a significant effect on the nitrification potential(p< 0.01),while the amorphous iron content did not have an obvious effect on the nitrification potential in the soil with pH value larger than 6.5.The soil with clay texture and high amorphous iron content could accelerate nitrification process,facilitating the transformation of NH4+-N into NO3--N.(3)There existed significant differences in denitrification potentials between the 24 sampled paddy soils which ranged from 0.13 to 0.97 mg N kg-1 h-1.The soils with higher organic matter content(X2,W2,W3,E3)had higher denitrification potential,while the paddy soil with lower organic matter content(T2,H1,H2)had lower denitrification potential.(4)The complex iron and amorphous iron in the soil have significant effect on the denitrification potential,while this was not for manganese.If only considering iron and manganese,the complex iron and amorphous iron contents are the most important factors affecting the denitrification potential(n = 24,p< 0.01,R2 = 0.454).