Strategies to decrease nitrate leaching in the Brimstone Farm Experiment, Oxfordshire, UK, 1988-1993: the effects of winter cover crops and unfertilised grass leys

摘要

Nitrate losses in drain flow were measured over five years on eight hydrologically isolated field plots, pairs of which had the following cropping regimes: (a) a 3-year unfertilised, ungrazed grass ley followed by winter and spring cereals, (b) mixed cropping including winter cover crops, spring cereals, winter cereals, winter fallow and spring beans, (c) a similar sequence to (b) but with a winter fallow replacing the cover crop in the first year and a winter cover crop replacing the fallow in thethird year, and (d) continuous winter cereals (control plots). Less nitrate was lost in winter drain flow from winter cover crops than from the winter fallows, but over all five years less nitrate was leached from the continuous cereal plots than from those with mixed cropping. Most of the extra nitrate lost from the mixed cropping regimes probably resulted from mineralization of the cover crop residues, which occurred at times when subsequent crops could not take advantage of the mineral nitrogen released. Crops grown after the grass ley and cover crops did not benefit from their residues, in terms of either grain yield or of total nitrogen uptake. On heavy clay soils in the UK a cropping regime of continuous winter cereals offers the best compromisebetween profitable crop production and minimized nitrate loss to surface waters.