The use of cover crops to reduce nitrate inputs to the Hampshire Chalk aquifer

Nitrate concentrations in groundwater abstracted from the Hampshire Chalk have increased over the last 20 years. Concentrations at a public water supply are now close to or above the drinking water standard and additional treatment will be required. Investigations of land use and nitrate source apportionment indicate that the largest contributor of nitrate entering the chalk aquifer comes from arable agriculture. Modelling has shown that, under present land use conditions, nitrate concentrations will continue to rise until the latter half of the twenty-first century. South East Water have successfully engaged with land managers and have trialled the use of cover crops at two sites close to the public water supply. Cover crops retain nutrients in the soil and improve soil condition as an integral part of crop rotation. Trials included different crop mixtures such as a variety of Raphanus sativus (oil radish), Vicia sativa (common vetch) and Trifolium alexandrinum/Trifolium incarnatum (clover). Trials were calibrated using porous pot installations and water extracted from the pots was analysed throughout the cover crop growing season. Results indicate cover crops can reduce nitrate concentration losses to the subsurface by up to 80%. Widespread use of cover crops could reduce nutrient leaching to the aquifer and provide a sustainable solution to current groundwater quality issues.