Defining the relationships between pasture production and soil P and the development of a dynamic P model for New Zealand pastures : a review of recent developments

Abstract A database was constructed comprising records from 2255 pasture phosphorus (P), potassium (K) and sulphur (S) field trials, of which 1799 included one or several rates of P. Subsets of this data were selected based on predetermined criteria to define the relationships between relative pasture production and available soil P (0–75 mm, Olsen P in μg P cm–3 soil)—the P production functions—for the major soil groups in New Zealand. These relationships, and their 95% confidence intervals, were defined using Bayesian statistics. For those soil groups for which there was sufficient data, the production functions were well defined and gave reasonably precise estimates of the relative pasture yield for a given Olsen P. For example, for the volcanic soils, the relative pasture production is most likely (P < 0.05) to be in the range 88–94% at Olsen P 25 and 98–100% at Olsen P 50. The shape of the production functions was similar for all soil groups—the relative pasture production increased with increasing O...