The impact on hydrology and water quality of woodland and set-aside establishment on lowland clay soils

Abstract

The hydrological and water quality implications of taking agricultural land out of arable production by establishing deciduous woodland and permanent set-aside, were monitored for 4 years, on clay soils in Cambridgeshire. Total runoff (surface and drainflow) from the woodland was between 20% and 30% of flows from adjoining arable land. Nitrate concentrations in drainage water from arable land were typically between 20 mg l −1 N and 70 mg l −1 N, whilst concentrations in measured ditchflow from set-aside were between 11 mg l −1 N and 15 mg l −1 N 1 year after conversion from arable, but declined to below 6 mg l −1 N the following year. Nitrate concentrations in drainage water from the woodland were always below 5 mg l −1 N. The results suggest that the lack of cultivation and deterioration of secondary drainage treatments associated with set-aside will increase soil surface compaction and surface runoff on clay soils. Large scale woodland establishment in mainly agricultural catchments may considerably reduce runoff whereas set-aside could increase flood risk. Both changes in land use reduced nitrate leaching losses.