Comparison of nitrate leaching from oats and Italian ryegrass catch crops following simulated winter forage grazing: a field lysimeter study

Intensive winter forage grazing systems have a high risk of environmental impact due to nitrate (NO₃⁻) leaching from urine deposition on cool, wet, fallow soils. We investigated the effect of sowing two catch crops after simulated winter forage grazing on kale to potentially reduce N leaching losses from a winter application of labelled ¹⁵N-urine (350 and 700 kg N ha⁻¹) using field lysimeters. The experiment measured the capture of N by the sowing at recommended dates of either oats (Avena sativa) or Italian (It.) ryegrass (Lolium multiflorum) and the resulting ¹⁵N balance. Results showed that the sowing of an oats catch crop reduced nitrate leaching by 25% over the critical winter–spring drainage period compared with It. ryegrass. Relatively small amounts of the labelled ¹⁵N-urine (3–4%) were captured in the catch crops of urine treatments so the reduced nitrate leaching under the oats crop was attributed to lower drainage over the period