Effect of the application of cow slurry to grassland on nitrate levels in soil and soil water contents

The effect of a single heavy dressing of unamended cow slurry, applied to grassland in early spring (March), on nitrate levels and moisture contents in the soil profile have been examined for a 12 month period after the application. The slurry was allowed to remain on the soil surface until late autumn, when it was cultivated and a pasture re‐established. Nitrate accumulated in the slurry and surface soil over spring, summer and autumn: the amount found in the slurry and 0–20 cm depth of soil in October (172 kg N/ha) accounted for 9% of the total‐N originally added in the slurry. Significant leaching of nitrate into the subsoil did not occur until the soil was subsequently rewetted to field capacity in late autumn and winter. The layer of slurry on the soil surface restricted moisture losses from the soil during summer to less than one half of those under untreated grassland. Restricted aeration under the slurry is considered to be an important factor in delaying nitrification and stimulating anaerobic activity in the soil so that deep leaching of nitrate may not be likely for several months after a heavy application.