Short-Term Irrigation Level Effects on Residual Nitrate in Soil Profile and N Balance from Long-Term Manure and Fertilizer Applications in the Arid Areas of Northwest China

Abstract

A field experiment was conducted to determine the effects of long-term applications of fertilizers and manure (1982 to 2003) and short-term irrigation level (2002 and 2003) on accumulation of nitrate nitrogen (NO₃-N) in soil at Zhangye Oasis, China. The treatments included manure (M) and no manure (M₀) as main plots; check (Ck), nitrogen (N), nitrogen + phosphorus (NP), and nitrogen + phosphorus + potassium (NPK) as subplots; and two amounts of irrigation (I₁ and I₂) as subsubplots. The application of N alone resulted in large NO₃-N accumulation in soil, accounting for 6% of the applied N, and the lowest crop N recovery. Application of manure resulted in increased NO₃-N in the soil profile compared to treatment with no manure, and the MN treatment resulted in the greatest amount of NO₃-N in soil. Nitrogen applied with P and/or K reduced the amount of NO₃-N in soil in both manure and no-manure treatments compared with N only. The unaccounted N was greatest (60%) in the N-alone treatment and lowest (30%) in the NPK treatment. When manure plus fertilizer were applied together, the unaccounted N ranged from 35%–42%. Based on results from only 2 years, greater amounts of irrigation (I₂) caused greater leaching of NO₃-N in the soil profile compared with I₁, especially in treatments receiving manure. The implications of these findings are that these high amounts of accumulated NO₃-N in surface and subsoil layers can be a potential threat to surface water, underground water, and air quality in the long run. This accumulated N in the soil profile can be used as a source of available N for future crops and should be recycled by using proper crop, soil, fertilizer, and water-management strategies/practices. The findings also suggest the need for further research to make an effective and efficient use of this accumulated NO₃-N in the soil profile in order to save cost of N fertilizer application to future crops.

Keywords:

• Apparent N recovery
• groundwater
• irrigation
• long-term fertilization
• manure
• nitrate accumulation and leaching
• N balance

Acknowledgments

We thank Prof. Xing Guang Xi for the helpful review. This research was funded by the Key Technologies Research and Development Program of China (2006BAD05B01 and 2006BAD04B06) and the importing talent support from ZAAS.