Effect of incorporated straw-nitrogen fertilizer on nutrient leaching in paddy soils

In a field experiment in Changshu Municipality of Jiangsu Province, the effect of incorporated straw-nitrogen fertilization on nutrient leaching in paddy soils was determined. The study shows that NH₄⁺-N, NO₃^--N and total N concentrations in leachate increase with increasing rates of nitrogen fertilizer. Compared with no-straw treatment, straw treatment presents lower NH₄⁺-N and NO₃^--N concentrations in surface water and leachate. Total N and NO₃^--N concentration in leachate collected from 30 cm soil depth is the highest in straw treatment, with the ranges of 1.09～12.76 mg·L^-1 and 0.76～3.74 mg·L^-1, respectively. Total P concentration in the leachate is in the range of 0.02～0.79 mg·L^-1 with higher concentration in leachate of 30 cm soil depth than of 60 cm soil depth. It is enhanced with increasing rates of nitrogen fertilizer. When nitrogen fertilizer application excesses 180 kg·hm^-2, NH₄⁺-N is the main form in leachate collected in 5～10 days after fertilization in the 30 cm and 60 cm soil depth. For all other times, NO₃^--N nutri-ent is the dominant form in leachate. Combined application of nitrogen fertilizer and wheat straw reduces nitrogen and phosphorus concentration in surface water and leachate, and improves fertilizer efficiency.