The effectiveness of cover crops during eight years of a UK sandland rotation

Growing cover crops during the winter before spring-planted crops is often suggested as an effective method to decrease nitrate leaching. A four-cours e crop rotation (potatoes-cereal-sugarbeet-cereal) was followed through two rotations on a sandy soil in the English Midlands. Three management system s were imposed on the rotation to test their effects on nitrate loss. The e ffects of cover crops on nitrate leaching and crop yields were compared wit h the more conventional practice of over-winter bare fallow before potatoes and sugarbeet. Cover crop N uptake was variable between years, averaging 25 kg ha(-1), whi ch is typical of their performance on sandy soils in the UK. The cover crop s usually decreased nitrate leaching but their effectiveness depended on go od establishment before the start of drainage. Over 7 years, cover crops d ecreased the average N concentration in the drainage from 24 to 11 mg l(-1) . Potato yield and tuber N offtake increased after cover crops. Ware tuber yield increased by an average of c. 8%; this was unlikely to be due to addi tional N mineralization from the cover crop because the potatoes received 2 20-250 kg fertilizer N ha(-1), and non-N effects are therefore implicated. Sugar yield was not increased following a cover crop. After 8 years of nitrate-retentive practices, there were no measurable diff erences in soil organic matter. However, plots that had received only half of the N fertilizer each year contained, on average, 0.14% less organic mat ter at the end of the experiment.