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

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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.