PHOSPHORUS BUDGETS FOR 2 CONTRASTING GRASSLAND FARMING SYSTEMS IN THEUK

Phosphorus budgets have been compiled for two contrasting grassland fa rming systems in the UK; intensive dairy farming and extensive hill sh eep production. Balance sheets of inputs, recycling of P through the s oil-plant-animal pathway; and outputs are presented to determine the p otential rate of P accumulation in the two systems. A typical 57 ha in tensive dairy farm with 129 lactating cows imports 2.48 t P via fertil izer, bedding and concentrates, plus a small amount from the atmospher e, of which 0.98 t are exported in milk, calves and transfer from soil to the aquatic environment. Therefore 1.5 t of P are retained within the farm each year, which equates to an accumulation rate of 26 kg/ha in the plant-soil system. This surplus occurs despite a fertilizer inp ut of only 16 kg/ha. However, a large proportion of P, equivalent to 2 7 kg/ha, is imported in feed concentrates. For the typical 841 ha hill sheep farm supporting 694 Blackface ewes, P inputs and outputs are 0. 66 and 0.42 t/yr, respectively Therefore, approximately 0.24 t P are r etained within the farm, which is equivalent to an accumulation rate o f 0.28 kg/ha per yr. In comparison to the small annual inputs and outp uts of P on the hill farm, much P 2.48 t, is recycled through the plan t-soil and plant-animal-soil pathways on the hill sheep farm. For both farming systems there is a net input of P although the rate of accumu lation is ten times greater for the dairy farm where the annual retent ion of P represents 60% of the total P inputs, compared with 36% on th e hill sheep farm.