Optimal site-specific fertilization and harvesting strategies with respect to crop yield and quality response to nitrogen

Incorrect fertilizer decisions can be costly if quality of the output, in addition to yield, is influenced by the application rate, which contrasts the flat payoff function estimated for fertilizer by previous studies focusing only on quantity. This study aims at modelling economic potentials of the combination of site-specific fertilization and quality specific harvesting at the example of wheat (Triticum aestivum L.), in Germany. Crop yield and protein response data to different nitrogen fertilizer applications were used from 15 locations to simulate site-specific wheat management. Four different management strategies were compared using a step wise price function for wheat qualities: uniform management, completely separate management, site-specific fertilization with uniform harvest, uniform fertilization with quality-specific harvest. It was found that opportunity costs (>50 €/ha) may apply, if threshold values for crop qualities are missed. Separation of different qualities can reduce this risk and create incentives for producing higher qualities on heterogeneous fields. Completely separate management had an economic advantage of up to 30 €/ha for the gross revenue, while site-specific fertilization alone had only marginal economic effects. However, these advantages have to cover costs for the use of technologies used, to be economically preferable.