Nitrate leaching from ploughed pasture and the effectiveness of winter catch crops in reducing leaching losses

Abstract

The effect of five catch crops (ryecorn, ryegrass, mustard, lupin, bean) on nitrogen (N) leaching following the autumn ploughing of a grass ley was compared with N leaching from bare fallow soil. The concentrations of nitrate N and ammonium N in the drainage water and the quantities of drainage water from the various treatments were measured over a winter period using undisturbed soil monolith lysimeters. Nitrate was the dominant form of N leached. The amount of N leached from soils with the ryegrass catch crop (2.5 kg N/ha) was considerably less than that leached from fallow soil (33 kg N/ha). Nitrate concentrations in the drainage water from soils growing ryecorn and ryegrass were less than 10 mg N/litre, whereas that from lysimeters growing lupins or beans and from the fallow soil exceeded this value. Shoot dry matter yield for mustard (5.91 t/ha) and ryecorn (5.25 t/ ha) was at least twice that of the other crops and very much higher than the 0.49 t/ha produced by the weeds in the fallow treatment. Nitrogen concentrations in the shoots ranged from 1.9 to 3.3% for the mustard and control plots respectively with the other crops averaging 2.2–2.6%. Total plant uptake of N by ryecorn (170 kg N/ha) was significantly higher than that by ryegrass, bean, and lupin (111, 96, and 99 kg N/ha respectively) and very much higher than the 39 kg N/ha taken up by weeds in the fallow plot. © 1996 Taylor & Francis Group, LLC.