Effects of Land Use on Soil Nitrogen and Its Transformation in Yellow River Delta

To investigate the effect of land use on soil nitrogen and its transformation in the slightly saline soil,soils under four types of land use were employed,i.e.,orchard,vegetable,cropland and unused new sedimentation land in Kenli County of Yellow River Delta.The results showed that the greatest total nitrogen in top soil layer(0—20 cm) was in the cropland,followed by orchard and vegetable land,and the least was in unused new sedimentation land soil.The mean value from the greatest to the least was 1.42,1.17,0.97 and 0.57 g/kg,respectively.In 20—40 cm soil layer,the average concentration of the total nitrogen was 0.86 g/kg in vegetable soil,which is higher than that in the other three land use types.The average concentration of NO-3—N in 0—20 cm vegetable soil layer is 27.25 mg/kg,far higher than that in orchard,cropland and unused new sedimentation land,while NH+4—N in different land use types was similar,ranging from 2.65 to 4.09 mg/kg.Soil NO-3—N and NH+4—N concentration in 20—40 cm layer in different land use soils showed the similar changes as those in top layer(0—20 cm).Through the correlation analysis,the available nitrogen in vegetable soil was mainly from fertilization,and the available nitrogen in orchard and crop land soils was closely correlated with the total nitrogen and was little affected by environment change.The concentration and transformation of nitrogen in unused new sedimentation land soil reflected the initial status of the study area.