ABILITY OF A DYNAMIC MODEL OF PHOSPHORUS TO ACCOUNT FOR OBSERVED PATTERNS OF RESPONSE IN A SERIES OF PHOSPHATE FERTILIZER TRIALS ON PASTURE

摘要

A national series of rates x forms of phosphate fertilizer trials gas provided a large amount of data on patterns of response of pasture production and soil P tests to forms, rates and frequencies of P fertilizer application over time. A simple mechanistic model of P in pastoral systems has been developed in an attempt to account for the observed patterns. The model considers active P in the soil to be in one of two compartments: undissolved fertilizer P (P-F) and a pool of labile, plant-available P (P-A). P dissolving from P-F enters P-A, and P is lost from P-A by immobilisation in the soil and by net removal above ground through non-recycled uptake by plants. Both these transfers are taken to follow first order kinetics, with rate constants designated K-1 and K-2 respectively. Pasture dry matter (DM) production in any year is related to the mid-year value of P-A by the diminishing-returns Mitscherlich equation, with nil pasture yield being associated with nil P-A.