Nitrogen leaching in an upland cropping system on an acid soil in subtropical China: lysimeter measurements and simulation

Abstract

The effect of rainfall and nitrogen (N) input on nitrate leaching in a rain-fed peanut–oilseed rape system on an acidic soil in subtropical China was investigated in a field lysimeter experiment from 1997 to 2000. Drainage and nitrate leaching were simulated using the Water and Nitrogen Management Model (WNMM). Nitrate concentrations in the drainage water and nitrate leaching increased with increasing N application rate. Annual leaching losses ranged from 21.1 to 46.3 kg N ha−1 (9.5–16.8%) for inputs between 0 and 150 kg N ha−1. Growth of oilseed rape decreased the nitrate concentration in the drainage water, but growing N fixing peanuts did not. Rainfall had a greater impact on nitrate leaching than crop uptake. Nitrate concentrations in the drainage water were relatively low (1.95–4.33 mg N l−1); this was caused by the high precipitation, the low nitrification rate, and the low residual nitrate in the soil. The loss of nitrate was low during the dry season (October–February) and in the dry year (rainfall 17% below average) mainly as a result of reduced drainage. WNMM satisfactorily simulated the inter-monthly variation in drainage and total nitrate leached, with respective relative root mean square errors of 42.7% and 70.2%, mean modelling efficiencies of 0.88 and 0.67, and mean relative errors of −3.82% and 21.8%. The modelled annual N losses were only 1–7% less than the observed values.