Economic control of fertilizer in highly productive pastoral systems. IV. An appropriate model for a stable upgraded state

Abstract

Data from a stable upgraded grass-clover system were used to show that an exponential model, based on the ideas of Liebig and Mitscherlich, may be simplified to permit a prediction of yields over years through three constant parameters for the fertilizer effect and one varying parameter for the climatic effect; this result is in accord with the Mitscherlich relative yield theory. When the model was applied to an economic analysis of the data, the result emphasized the importance of the concept of an average year in calculating fertilizer recommendations; also, it became apparent that completely unfertilized plots should be excluded from field trials intended as a base for such economic advice.