Changes Of Nitrogen Mineralization And Nitrification And Denitrification In Northeastern China Black Soil Under Different Water Conditions

The black soil region of northeast China is located in the temperate semi-humid monsoon climate zoon.The farmland soil moisture changes frequently due to the climate characteristics making the different soil moisture history and drying-rewetting alternate phenomenon exsit generally.Soil water regime is a regulation factor of soil nitrogen transformation.Meanwhile,mineralization,nitrification and denitrification are important processes of nitrogen transformation which have certain impacts on it.The simulated experiments were conducted by using the black soil collected from the Key Observation Station with a laboratory incubation method to study the changes of mineralization,nitrification and denitrification rate under diffirent soil moisture,and explore the effects of different water conditions,especially the water history on the nitrogen transformation.In order to establish the reasonable evaluation of nitrogen transformation in balck soil,also providing the basis for soil nutrient management and environmental protectionIn the process of gradient increasing the soil moisture,the largest rate of mineralization and nitrification are both appeared at 80%WHC moisture content.At this point mineralization and nitrification have the strongest effect.The maximum denitrification rate appeares at 100%WHC water content.Nitrogen mineralization,nitrification and denitrification are more significantly influenced by four times than by once under diffirent N-application conditions.When the soil in the low water content,mineralization and nitrification play the leading role,with the increase of water content,the denitrification effect is more and more intense.In additon,the strength of mineralization,nitrification and denitrification could be different due to distinct antecedent water under the same water content.In drying-rewetting cycle experiments of 40%WHC and 80%WHC,compared with the constant 40%WHC and constant 80%WHC water content,the effect of dyying-rewetting cycle on mineralization is not obvious.Nitrification rate of soil samples treated by alternative drying-rewetting is lower than other samples.When deionized water was add to the drying-wetting cycle,and the water content was transferred to 80%WHC,nitrification rate has a decreasing tendency.Compared with soil treated by 80%WHC,drying-rewetting cycle is more conductive to the denitrification.Contrast to the same water content in two different processes,although the soil in the same soil water content,changes of mineralization and nitrification rate by dry to wet are significantly less than from wet to dry process.Meanwhile,denitrification variation is more than that from wet to dry process.It shows that dry wet alternation has a certain effect on nitrogen transformation.Five pre-water treatmented soil samples incubated at four different water contents,can be discovered that in the 60%WHC instant moisture content.the mineralization rate of fresh soil shows the most response to the soil moisture,nitrification second.Denitification is higher than low moisture soil but weaker than the other three pre-treatment soil samples.Although the difference of mineralization rates is not significant,the changes of nitrification rate and denitrification rate are obvious under five pre-water treatments.The history of soil moisture has a strong influence on nitrification and denitrification,while the effect on mineralization is small.It can be indicated that the antecedent water treatment makes a certain effect on nitrogen transformation.