End of Project ReportThirty years of research involving phosphorus (P) fertiliser rates
(0, 15 and 30 kg/ha/yr) on pastures has been completed. Beef
performance on pasture at relatively low and high stocking rates
was determined by weighing beef animals (mean wt = 260kg) at
the beginning and end of each grazing season for 18 years. Soil
samples were taken at various times and at various depths. Live
weight gain (LWG) was greatest at the high stocking rate (HSR)
compared to the low stocking rate (LSR). LWG maximised at 15
kg P/ha. Maximum beef production took place with a soil test of
6 mg P/l using the Morgan’s procedure. Most of the soil P and
fertiliser P, as measured by both the Morgan’s and Total P
procedures, were in the top 10cm. However, a significant portion
moved below that to the 10-20 cm layer, as determined by both
Total and Morgan’s P in both P treatments. Soil P and fertiliser P
as determined by the Morgan’s procedure moved into the 20-40
cm layer but no lower. Work done on the 30 kg/ha P treatment
and on another site at Johnstown Castle showed that significant
amounts of P moved off the plot with water in overland flow and
the loss was related to the soil test (Morgan’s) for P. The amount
of P lost per unit of Morgan’s was calculated to be 175g with a
Morgan’s soil test of 4 mg P/l and 281g with a soil test of 17 mg
P/l.
A mass balance procedure was attempted for the 30 years’ work
to determine how much P was exported in beef, lost in overland
flow or retained in the soil. This showed that fertilising beyond
15 kg/ha gave no increase in beef production and that the extra
P was found in the soil, or lost in overland flow. When 15kg P/ha
was applied annually for 30 years it was estimated that 20% and
4% of P applied was removed in beef or lost in overland flow,
respectively. It was calculated that 76% of the P applied stayed
in the soil
