Dynamics And Leaching Characteristics Of Soluble Organic Nitrogen In Paddy Soils Under Long-term Different Fertilization Management

Soluble Organic Nitrogen(SON)plays an important role in farmland ecosystem for nitrogen cycling.In the paddy ecosystem,various amount and forms of nitrogen fertilizer were applied into soil in a long-term,yet the quantitative research and migration patterns of the SON remains unclear.Dissolved Organic Nitrogen(DON)in soil solution and drainage waters could be flowed into surrounding water with the surface runoff,or entered into groundwater by eluviation,resulting in environmental effects and ecological risks.Therefore,the aims of the present research were to study the dynamic changes of paddy soil SON with the paddy growth stage and the migration pattern of DON with depth profiles of four different long-term fertilization(no fertilizer(CK),fertilizer(NPK),fertilizer + cattlemanure(NPKM),fertilizer +straw(NPKS))in a red paddy soil.The paddy soil and soil leachate during rice growth period were collected,and the ebb and flow of relations between the SON and DON,and environment effect were analyzed.Based on physical and chemical properties of soil,the main control factors of dynamic change and migration of SON content under the condition of long-term different fertilization were discussed.The information provided basis for consummating the farmland soil nitrogen cycle theory and evaluating farmland nitrogen leaching risk and strengthening the management of field water.The results are as follows:(I)SON in paddy soil mainly existed in the surface layer,and had gradually migrating down.Before the paddy transplanting,SON content on the depth of 0-20 cm were107.78%-220.65%and 269.39%-374.06%higher than those on the depth of 20-40 cm and 40-60 cm respectively,SON content on the depth of 20-40 cm were 47.84%-77.78%higher than on the depth of 40-60 cm,these results implied that the same processing of soil SON between different depths appeared as 0-20 cm>20-40 cm>40-60 cm,and on the depth of 0-20 cm,soil SON concentration significantly greater than 20-40 cm and 40-60 cm,but between 20-40 cm and 40-60 cm,they were no obvious difference,with the deeper the depth,SON migrating down to decrease.(II)Soil physicochemical and biochemical properties had significant effects on the SON.Grey slope-correlation analysis showed that pH and the density had negative effects on soil SON,the others had positive influence on soil SON,and soil organic matter had most influence on soil SON,the influence degree of SON was found to be in the order of soil organic matter>Microbial Biomass Nitrogen(MBN)>total nitrogen>glutaminase>aeration porosity>protease>pH>the density.(III)In the paddy growth period,the overall trend of the soil in each treatment was fluctuation.SON concentration had difference between different treatments in different paddy growth period.Earlier stage:NPKM>NPKS>NPK>CK;Medium-term:NPKM>NPK>NPKS>CK;later period:NPKS>NPKM>NPK>CK.(IV)In the paddy growth period,the changes of DON concentration on flooded layer were influenced by fertilization.DON concentration of different treatmeats showed up NPKM>NPKS>NPK>CK on earlier stage.later period appears NPKM>NPKS>NPK>CK.NPK?NPKM and NPKS were significantly higher than CK,and had relatively consistent trend,both in 2-10d shrinking fast,rising after 15d,there was a small peak to 20 d,then reducing,finally tends to be stable.These indicated that DON content were obviously improved by fertilization,and the period that easy to lost mainly in paddy transplanted the first 20d,so field water management should be paid attention to in this period.(?)In the paddy growth period,DON concentration gradually reduced with the depth increased,DON concentration difference under different fertilization measures mainly appeared in 0-20 cm soil layer.The migration of DON showed there were obviously changes before 35d after planting,and no significant difference after 35d.Before 35d after planting,the SON concentration on the depth of 0-20 cm were 58.12%-1084.79%higher than those on the depth of 20-40 cm,SON concentration on the depth of 20-40 cm were 3.87%-388.67%higher than on the depth of 40-60 cm,these proves that the size of DON concentration showed 0-20 cm>20-40 cm>40-60 cm.