In studies of the most economical level of fertilizer to be applied to a crop, it is usual to assume that the price which the crop will command is a known constant. This assumption may not be realistic where the price structure is related to the quality of the crop; for example where a premium is payable according to a measurable quality characteristic, and this characteristic is influenced by the fertilizer dose. Previous work developed a Bayesian approach to finding the optimum fertilizer level when the crop price is constant. That approach incorporates expert knowledge of the crop and soil conditions, and can encompass a choice of variety and fertilizer level. The procedure is extended to model the distribution of the quality characteristic, and hence that of the crop value, at a target location. An example is given in which a premium is offered for barley grain with low levels of nitrogen. The choices of fertilizer level and variety are found to be robust to changes in the dose-response functions for yield and grain nitrogen concentration and in the prior distribution of variance components.