A comparative study of nitrate leaching from soils of differing textures under similar climatic and cropping conditions

Abstract

This study reports a direct comparison of nitrate leaching on a field scale from a sandy soil overlying a relatively impermeable glacial till ( K sat = 30−50 mm day −1), with that from a clay loam soil overlying a similar glacial till ( K sat = 2−8 mm day −1), under nearly identical climatic and cropping conditions. Drained plots were installed at each site, and N application rate on the plots, which grew spring barley, varied from 0 to 210 kg N ha −1. Nitrate concentrations in drainage water from the two sites were measured using a simple flow-weighted sampling device and drainflow was measured using tipping bucket flow meters. Total leaching losses (including an estimate of deep percolation) in the first year of the comparison were not significantly higher on the sandy site (38 ± 11 kg N ha −1 at 150 kg N ha −1 N fertiliser application) than on the clay loam site (27 ± 4 kg N ha −1). In the subsequent 2 years, leaching losses increased at the sandy loam site. At the clay loam site leaching losses were much lower (7–11 kg N ha −1) in the final year). Timing of cultivation was an important factor influencing the amount of leaching in the clay loam soil. The effect of applied N fertiliser on nitrate leaching was small at both sites, except in the final year at the sandy site, which leached 105 kg N ha −1 at the highest fertiliser rate. The interpretation of these results was aided by concurrent chloride leaching experiments. These experiments showed that the residence time of a substantial proportion of chloride (40–50%) was longer than 1 year. This may be because of diffusion and slow convection into the glacial till horizons, where the residence time is long.