Rv. Smith et al., INCREASE IN SOLUBLE PHOSPHORUS TRANSPORTED IN DRAINFLOW FROM A GRASSLAND CATCHMENT IN RESPONSE TO SOIL-PHOSPHORUS ACCUMULATION, Soil use and management, 11(4), 1995, pp. 204-209
Because of the observed variability in soil available P (Olsen) conten
ts, phosphorus budgets were used to predict changes in the soil P stat
us of an intensively managed 6 ha grassland catchment in Northern Irel
and. The P accumulation rate of approximately 24 kg/ha/y suggested an
increase of soil available P (Olsen) of 1.0 mg P/kg/y. Soluble reactiv
e phosphorus concentrations in drainflow measured on a daily basis for
a two year period (January 1981 - December 1982) were compared with t
he two year period January 1990 - December 1991. The median concentrat
ion had increased by 10.0 mu g P/l in 1990/91 compared with 1981/82. T
his difference was only apparent in mean concentrations for the two ti
me periods, after data associated with high flow events, which were mo
re frequent in 1981/82, were excluded from the comparison. This rate o
f increase of 1.1 mu g P/l/y, which was interpreted as reflecting an i
ncrease in soluble reactive phosphorus concentration in soil solution,
is comparable to the increase in background soluble reactive phosphor
us of 1.5+/-0.54 mu g P/l/y which was reported recently over a 17 year
period from diffuse sources in the much larger (4400 km(2)) Northern
Ireland catchment of Lough Neagh.