Combining mechanical control of couch grass (Elymus repens L.) with reduced tillage in early autumn and cover crops to decrease nitrogen and phosphorus leaching

Abstract

Methods for control of couch grass (Elymus repens L.) with reduced tillage and cover crops to achieve low risk of nitrogen (N) and phosphorus (P) leaching were investigated. Treatments with reduced post-harvest tillage (one or two passes with duckfoot cultivator), hoeing between rows in combination with a cover crop, and a cover crop mown twice during autumn were compared with treatments with conventional disc cultivation and the control without tillage or cover crop. The study was conducted on a sandy soil in Sweden with measurements of N and P leaching. A 2-year experimental protocol was used, repeated twice. Treatments were implemented in the first year, and effects on couch grass (shoot density, shoot and rhizome biomass) were measured during autumn and in the second year. Significant effects of a single duckfoot cultivation and cover crop strategies were observed on couch grass shoot density in autumn but persistent effects were not verified. In conclusion, a single cultivation after harvest instead of repeated reduced the risk of N leaching and a cover crop in combination with hoeing or mowing effectively reduced it. Repeated cultivations resulted in mean annual N leaching of 26 kg N ha−1 compared with 20 kg in the treatment with one cultivation, 17 kg in the control, 16 and 12 kg in cover crop treatments with mowing and hoeing, respectively. The P leaching was small (0.04–0.09 P ha−1 year−1), but there were indications of increased P drainage water concentrations in the treatment with a cover crop which was mown.