Long-term phosphorus grassland experiment for beef production - impacts on soil phosphorus levels and liveweight gains

Phosphorus is essential for plant and animal health. The aim was to determine the impacts of P fertilizer on changes in Morgan's soil test P (STP) and liveweight gain (LWG) of mature beef animals over the last 10 yrs (1999-2008) of a 40 yr P experiment on temperate permanent grassland in north-western Europe. There were three original treatments: 0 (P0), 15 (P15) and 30 (P30) kg/ha/yr P for 40 yrs (1968-2008), and three new treatments on the same area that started in 1999: P0 for 30 yrs then 30 kg P/ha/yr for 10 yrs (P0-30), P15 then 5 kg P/ha/yr (P15-5) and P30 then zero P (P30-0). Six plots (0.18 0.27 ha) per treatment were rotationally grazed by beef animals from April to October. The STP levels on the three original treatments were stable over the last 10 yrs and averaged 2.4 (P0), 5.8 (P15) and 16.0 (P30) mg/L soil. The STP decreased from 18.0 to 8.5 mg/L in the P30-0 treatment, from 6.5 to 5.0 mg/L in the P15-5 treatment and increased from 2.4 to 4.8 mg/L in the P0-30 treatment. Liveweight gains were lowest on P0 but similar on the other treatments (mean of 651 compared to 988 kg/ha/yr). It is concluded that of the order of 4-6 mg/L STP and a fertilizer input of 810 kg/ha/yr P was adequate for beef production on a grazing system under the conditions of this experiment.