LONG-TERM FERTILIZER FIELD TRIALS - COMPARISON OF 3 MATHEMATICAL RESPONSE MODELS

Accession to the European Union caused a drop of nearly 60 per cent fr om 1994 to 1995 in prices of wheat, barley and oats in Finland. The ec onomic use of fertilizer therefore decreased accordingly. To calculate the effect of the price changes on the economic optima, the physical production function must be known. Three physical production functions , the quadratic, the linear response and plateau (LRP) and the exponen tial function were estimated for this purpose. The models differed lit tle in respect of the R-adj(2) value (0.82-0.90) but the calculated op timum varied, depending on the production function. Data on a long-ter m field trial (21 years) were analysed. The field trial was establishe d in 1973 to demonstrate the effect of mineral fertilizer in crop prod uction. The crops grown in the trial were barley, wheat and oats. Diff erent varieties were included in the models.