Effects Of Water Condition And Nitrogen Application On Nitrogen Transform In Paddy-Upland Rotation

Paddy-upland rotation is one of the most important rotation systems around Yangtze River, and plays an important role to ensure food security in our country. The transformation of soil nitrogen is affected by perennial drought alternating. It is not effective to know soil N supply by testing soil inorganic nitrogen concentration in paddy upland rotation system. Water and soil condition are the important factors affecting the transformation of soil nitrogen in this system. Combining the field experiment with culture test, it is said that the effect of N fertilizer on soil total nitrogen and organic nitrogen stock in paddy-upland rotation was studied compared with the other rotation system.In culture test, it is explored for the effects of N application and soil textures on transformation of SON and soil organic N.The main results are as follows:The concentration of total nitrogen in the soil was increased for N application,and was increased by 16.80%-24.97% and 13.57%-23.50% in the rice-rapeseed rotation and cotton- rapeseed rotation in 3 years.There is no significant difference in soil total nitrogen concentration, but the increase rate of N stock in a year in paddy-upland is higher than that in cotton- rapeseed rotation. It is difference to the effects of nitrogen fertilizer and rotation systems on soil organic nitrogen pool, AN,AAN and HUN were affected by N application.ASN concentration was affected by rotation systems, and it is more concentration of ASN in paddy-upland rotation than that in.the other rotations.The concentration of inorganic nitrogen in the soil was significantly increased by N application. And in the flooded conditions,the soil ammonium nitrogen concentration was significantly higher than that in dry land simulation processing. after three months of training, soil ammonium nitrogen concentration was decreased significantly for the flooded treatment being into dryland cultivation, but the nitrate nitrogen concentration in soil did not be increased significantly.The soil ammonium nitrogen concentration did not be increased for water conditions changed.The parts of soil organic N was affected by N application under water conditions.AN concentration and ASN concentration were increased by flooded water,and AAN concentration was increased in dryland condition.N in fertilizer would be transformed to AN first,and then would be into ASN and HUN.In the dryland condition,N in fertilizer would be into AAN,and it would be transformed to HUN.The soil organic N would be into ASN and AN for flooding.N transformation was significantly affected by soil textures under water conditions.The increase of soil AN concentration in sand and silty clay loam is mainlyaffected by water conditions.It is more significant to increase AN concentration in flooded condition for N application in the soil of clay loam.The concentration of AN in sand and clay loam was significantly decreased after the flooding changed to dry land.In the dry land,it is useful to increasing AAN concentration for N application in clay loam,but the concentration of AAN was decreased in the sand and silty clay loam.The AAN concentration was decreased about 80 mg/kg-100 mg/kg in silty clay loam and about 20mg/kg-40 mg/kg in sand.After that,AAN would be transformed into HUN in soils.