Soil phosphorus extractability and uptake in a Cirsio-Molinietum fen-meadow and an adjacent Holcus lanatus pasture on the culm measures, north Devon, UK

摘要

The seasonal pattern of extractable soil P and soil solution P was determined for topsoil samples taken from a Cirsio-Molinietum fen-meadow community, and also for an adjacent agriculturally improved pasture in Devon, UK. Phosphorus concentration was investigated using three methods during 1993; Olsen's reagent (sodium bicarbonate) for soil P, centrifuging and polymeric suction cups for soil solution P. Solutions were extracted at two-weekly intervals during the spring and at monthly intervals during the summer. Phosphorus removed from both sites by centrifuging was in the range 5-30μg/dm3 soil, in comparison with 1-6 mg/kg for Olsen P. Olsen P on the Cirsio-Molinietum was lower than on the improved pasture in mid-March and mid-June. The concentration of P in soil solution removed by suction cups was below the level of detection (<2μg/dm3) on the Cirsio-Molinietum. Suction cup P on the improved pasture peaked in April and May at 16-19μg/dm3 soil. Herbage yield and P concentration were measuredthroughout the growing season. Above-ground standing crop was greater on the Cirsio-Molinietum than the improved pasture at the beginning of the grazing season, because of the large litter component on the former. Total P content of this material was only 1.81 kg P/ha on the Cirsio-Molinietum, in comparison with 5.58 kg P/ha on the improved pasture. Phosphorus concentration of plant material obtained by repeated defoliation was～1.0 mg P/g DM on the Cirsio-Molinietum, whereas a clear seasonal trend, peaking at 3.5 mg P/g DM, was observed on the improved pasture. Phosphorus concentration of litter, grass and sedge from ungrazed plots on the Cirsio-Molinietum indicated distinct seasonal variations for the grass, with no seasonal pattern for the sedge component.