Nitrate Leaching from Intensively Grazed Swards

Keywords: Nitrate leaching, Grazed grass, Pasture, Cut swards.

The effect on nitrate leaching of a change in management of intensively grazed swards was tested on three sites for two or three years. Cattle were allowed to graze throughout the season, or removed in either June or July, with subsequent grass growth cut for silage. It was hoped that the reduction in nitrogen returns via dung and urine, at a time of year when grass uptake of nitrogen is falling, would reduce the quantity of nitrate in soil in autumn, and hence the quantity of nitrate leached. Nitrogen removal in herbage varied from 6 to 257 kg/ha. Yields were severely restricted by drought in some years. Nitrate leaching was on average reduced, but the effect was variable, especially for the intermediate treatment where cattle were not removed until July.

Earlier work on a clay soil in an area with higher average rainfall had indicated potential for significant impact on leaching. It is concluded that the effect of cutting instead of grazing in late summer may be less reliable on droughty soils and in dry areas. Detailed comparison with alternative strategies, including spring cutting, is needed. Future studies also need to take into account the practical impact of poor grass growth on stock management and manure returns, to ensure that conclusions can be extended to the whole farm situation.

E I Lord, ADAS Rosemaund, Woodthorne, Wergs Road, Wolverhampton, UK.

28 pages, 6 figures, 6 tables, 17 references.