Evaluation of mapping and on-line nitrogen fertilizer application strategies in multi-year and multi-location static field trials for increasing nitrogen use efficiency of cereals

Mapping and on-line (sensor) variable rate nitrogen fertiliser application strategies were tested in static field trials for three years and in several locations. We determined whether they can enhance nitrogen use efficiency of cereals as compared to optimal uniform nitrogen application while still maintaining yields. In general, high yields were found on field sites representing moderate infield variability. Despite highly contrasting weather conditions between years, similar responses were observed between lower and higher yield zones and the effects of the different strategies were found to be relatively consistent. The results indicate considerable potential to increase nitrogen use efficiency while simultaneously maintaining yields. The mapping approach, which considers the long-term yield potential, indicated substantial gains for the environment in areas of lower yield productivity and fertile colluvial deposit zones with average savings of 34 and 17 kg N ha^-1, whereas the sensor approach led to a reduction in nitrogen application on sites with high yield productivity of about 8 kg N ha^-1. A combination of the approaches could further increase the benefit for the environment and represent a new standard for the good code of agricultural practice in heterogeneous fields.