Effects of Glucose Addition on N Transformations in Paddy Soils with a Gradient of Organic C Content in Subtropical China

To better understand the interaction of N transformation and exogenous C source and manage N fertilization,the effects of glucose addition on N transformation were determined in paddy soils with a gradient of soil organic C content.Changes in N mineralization,nitrification and denitrification,as well as their response to glucose addition were measured by incubation experiments in paddy soils derived from Quaternary red clay in subtropical China.Mineralization and denitrification were changed in order of increasing soil fertilities: high>middle>low.During the first week of incubation,net N mineralization and denitrification rates in paddy soil with high fertility were 1.9 and 1.1 times of those in soil with middle fertility and 5.3 and 2.9 times of those in soil with low fertility,respectively.Addition of glucose decreased net N mineralization by approximately 78.8,109.2 and 177.4% in soils with high,middle and low fertility,respectively.However,denitrification rates in soils with middle and low fertility were increased by 14.4 and 166.2% respectively.The highest nitrate content among the paddy soils tested was 0.62 mg kg-1 and the highest nitrification ratio was 0.33%.Addition of glucose had no obvious effects on nitrate content and nitrification ratio.It was suggested that the intensity of mineralization and denitrification was quite different in soils with different fertility,and increased with increasing soil organic C content.Addition of glucose decreased mineralization,but increased denitrification,and the shifts were greater in soil with low than in soil with high organic C content.Neither addition of glucose nor inherent soil organic C had obvious effects on nitrification in paddy soils tested.