Nitrate leaching from grassland

Increased awareness of the economic importance of losses of nitrogen (N) from agricultural land, together with the recognition that nitrate in drinking water is potentially detrimental to human health, have stimulated research on nitrate leaching1–4. Various reports5–7 have suggested that the leaching of nitrate from arable land is the major source of nitrate to water supplies in east and south-east England. In contrast, leaching from grassland is thought to he small5,8–10. However, this conclusion has been based largely on studies of leaching below cut swards, which exclude the effect of ruminants (cattle and sheep) on nitrate loss. This effect is likely to be substantial as <20% of the input of N to grassland systems is recovered in products of the ruminant animal11. Our study demonstrates that the amount of nitrate leached below a grass sward grazed by cattle was 5.6 times greater than that leached below a comparable cut sward and exceeded the losses normally observed from arable land.