Sheep faeces in relation to the phosphorus cycle under pastures

Abstract

Faeces from sheep grazing naturalDanthonia pastures and improved subterranean clover pastures have been analysed for total phosphorus and inorganic phosphate over a period of 2 years. Both total and inorganic phosphorus contents (milligrams P per gram) varied widely with type of pasture and with season. The variation in organic phosphorus content (by difference) remained, relative to total phosphorus, fairly constant throughout. Total phosphorus content varied from 1.8 to 17 mg P/g whilst organic phosphorus varied from 1.5 to 4.0 mg P/g. Sheep grazing the improved pastures voided approximately 2.5–3 lb P as inorganic phosphate and 0.5–0.75 lb P as organic phosphorus per sheep per year. The inorganic phosphate was readily soluble in acid but not in water and was readily available to wheat grown in pot culture. The organic phosphorus was not readily available to plants and was not rapidly mineralized to inorganic phosphate. The contribution faecal phosphorus makes to the nutrition of pastures and to the reserve of soil organic phosphorus is briefly discussed.