Nitrate leaching under spring barley is influenced by the presence of a ryegrass catch crop: Results from a lysimeter experiment

The influence on nitrate leaching of ryegrass (Lolium perenne L.) used as a catch crop in spring barley (Hordeum vulgare L.) was investigated during three successive years in a lysimeter experiment on a sandy loam soil. Four treatments were included with combinations of time of tillage (November/March) and handling strategy of the aboveground ryegrass biomass (return/removal). Reference plots tilled in March were sown to spring barley alone. The four fertilization levels initiated 15 years earlier were continued with barley either left unfertilized, or receiving 11 g N m−2 year−1 (1N) in mineral fertilizer or with 1N or image (16.5 g N m−2 year−1) in pig slurry. The ryegrass reduced nitrate leaching by 1.4–4.3 g N m−2 year−1 when incorporation took place in November. If incorporation was carried out in March, reductions in nitrate leaching were 2.1–5.6 g N m−2 year−1. The herbage cut of ryegrass had accumulated 1.0–2.4 g N m−2 year−1 and 0.9–2.1 g N m−2 year−1 in November and March, respectively. Nitrate leaching losses increased with higher rates of N both with and without a catch crop. At the highest N rate (image in slurry), the incorporation of the herbage cut of the ryegrass raised nitrate leaching compared with removal. At the other three fertilization levels, return of the herbage did not significantly affect nitrate leaching. Grain yield and N uptake of the spring barley were unaffected by a catch crop and the management strategy did not interact with N fertility level. The study showed that growing a ryegrass catch crop repeatedly for three years was effective in reducing nitrate leaching losses, but the retained N did not have any immediate beneficial effect on spring barley grain yield.