Dynamics of nitrogen in double-rice paddy soil under application of chemical fertilizer combined with manure

A six year field experiment was conducted in Quaternary Period red clay soil in double rice region of south Hunan province. Its purpose was to disclose dynamics and transferred characteristics of nitrogen under the application of chemical fertilizer combined with manure. Four treatments, namely, no nitrogen (PK), swine manure (M), chemical fertilizer (NPK) and swine manure applied combined with chemical fertilizer (NPKM) were selected to study the dynamics of total nitrogen and inorganic nitrogen in surface water, and as well as the dynamics of inorganic nitrogen in soil solution in different layers (25-30，55-60 and 85-90cm) and tillage soil. The results show that NH4+-N is the predominant inorganic nitrogen in red double rice paddy soil, and the ratio of NH4+-N/total N reaches to 0.5–0.9 in surface water within 1-3days after chemical fertilizer (NPK treatment) applied, while that of organic manure treatment is about 0.3. The peak values of nitrogen concentration are detected within 1-2 days in surface water and 3-5 days in soil solution in different layers after fertilizer application. The peak values of nitrogen concentration in surface water, in soil solution and in tillage soil are lower in organic manure (M), and chemical fertilizer applied combined with organic manure (NPKM) treatments than those of the other two treatments. The NPKM treatment achieves a 12.2 t/hm2 mean annual yield (68% higher than that of PK). The soil organic matter in tillage soil is increased by 18.5% during the six-year plantation at the NPKM which is significantly higher than that of the NPK treatment. Application of chemical fertilizer combined with organic manure is propitious to reduce environment load due to excessive chemical nitrogen applied.