Abstract:

【Objective】 To provide a reference for scientific fertilization in the dry-land，present study on the changing trend of NO3--N leaching and the relationship between NO3--N accumulation and fertilizer rates in the farmland ecosystem based on data of the long-term fertilizer experiment. 【Method】Soil samples were collected per 20 cm in 0-300 cm soil layer, after being extracted with 1 mol?L-1 KCl, the NO3--N concentration in soil was analyzed with AA3 automated flow injection analyzer. 【Result】 When N fertilizer was applied alone, the accumulation peaks of NO3--N occurred in 80-100 cm and below 300 cm soil layer. If the annual rate of N reached 180 kg hm-2, total NO3--N accumulation amount in 0-300 cm soil layer was 8 times the amount of annual N application. When P fertilizer was applied alone, it had no significant effect on NO3--N distribution. NO3--N accumulation amount in the soil enhanced significantly with increasing N application rates. When N and P fertilizer was applied in combination, the application of P fertilizer alleviated NO3--N leaching and the positive effect increased with increasing N application rates. When N rates were excessive, even combined with P fertilizer, NO3--N penetrated into deep soil layer and accumulation peaks were found in 100-120 cm and 240-260 cm soil layers. Quadratic polynomial regression equation could reflect the relationship between NO3--N accumulation and N, P fertilizer rates. 【Conclusion】 When N fertilizer was applied excessively for 23 years, NO3--N penetrated largely into deep soil layer and two accumulation peaks were observed. However, NO3--N leaching could be mitigated by combined application of nitrogen and phosphorus. Long-term fertilizers application at rates for maximum yield would result in a great amount of NO3--N accumulation in deep soil layer in dry-land wheat field.

Key words: long-term fertilizer application, NO3--N leaching, dry-land, nitrogen, phosphorus