Phosphorus budgets for two contrasting grassland farming systems in the UK

Abstract

Abstract. Phosphorus budgets have been compiled for two contrasting grassland farming systems in the UK; intensive dairy farming and extensive hill sheep production. Balance sheets of inputs, recycling of P through the soil–plant–animal pathway and outputs are presented to determine the potential rate of P accumulation in the two systems. A typical 57 ha intensive dairy farm with 129 lactating cows imports 2.48t P via fertilizer, bedding and concentrates, plus a small amount from the atmosphere, of which 0.98t are exported in milk, calves and transfer from soil to the aquatic environment. Therefore 1.5t 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 input of only 16 kg/ha. However, a large proportion of P, equivalent to 27 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 0.24t P are retained within the farm, which is equivalent to an accumulation rate of 0.28 kg/ha per yr. In comparison to the small annual inputs and outputs of P on the hill farm, much P, 2.48t, is recycled through the plant‐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 accumulation is ten times greater for the dairy farm where the annual retention of P represents 60% of the total P inputs, compared with 36% on the hill sheep farm.