Long-term changes in soil fertility and pasture production under no, low and high phosphorus fertiliser inputs

Abstract

Many hill country farmers have struggled to maintain fertiliser inputs in recent years. The long-term fertiliser and sheep grazing farmlet study at the AgResearch Ballantrae Hill Country Research Station provides invaluable insights into the benefits of continued annual inputs of phosphorus (P) fertiliser on production levels and the farm business, and also the implications to the production system when fertiliser is withheld. Since detailed monitoring stopped in 1990, the fertiliser treatments have been maintained, along with nominal sheep stocking rates and grazing practices. Occasional measurements of soil fertility have also been made on the farmlets that have received either no fertiliser inputs for 30 years, a low annual fertiliser input (125 kg superphosphate (SSP)/ha/yr), or a high input (375 kg SSP/ha/yr) for 35 years. In this paper changes in sheep stocking rate and soil fertility are reported and compared with earlier published data from this longterm site. This field study provides a valuable resource for ongoing research into nutrient requirements and cycling in hill land environments, and a visual demonstration of the continued importance of fertiliser application as a driver of hill country production. Keywords: Livestock production, P fertiliser, Olsen P, long-term sites