Introduction. In traditional farming, fertilizers are applied homogeneously on the agricultural fields taking into account the average crop recommendation. As most fields are not homogeneous, this results in overfertilization of certain zones and underfertilization of other zones. The excess of nitrate leaches to the surface and groundwaters which causes problems with the water quality. Precision fertilizer management has been proposed to reduce these negative effects. However, most studies on precision fertilization focused on the use of chemical fertilizers with known concentration of nutrients, while many farmers involve animal manure in their fertilization practice. Therefore, the goal of this research is to assess the crop yield and environmental responses for different scenarios of precision manure management.

Materials and methods. In this study, seven agricultural fields in Flanders with different soil types (sandy, loamy) were selected. Using soil maps, NDVI time series, and maps of electrical conductivity, 2-3 management zones with a potentially different crop productivity were identified in each field. In the spring of 2020 and 2021, field trials with maize were set up in these zones to investigate the best fertilization strategy. Fertilization scenarios included conventional practice, +20% and -20% of fertilizer dosage compared to conventional practice. At the end of the growing season, the maize yield was quantified for each trial plot and residual nitrate in the soil was measured to assess the potential environmental impact in terms of nitrate leaching after the harvest.

Results and discussion. For most fields, yield results demonstrated a good correspondence with historical NDVI maps and clear differences in yield were observed between the management zones. In most zones with a lower crop productivity potential, 20% reduction in fertilization did not result in a significant yield reduction, but resulted in a significantly lower residual nitrate at the end of the growing season. On the other hand, increased fertilization of the zones with a high crop productivity potential, generally resulted in a higher yield and did not cause a change in the residual nitrate.

Conclusion. The field trial results indicate that in most fields where significant historical variation was observed, precision fertilization outperformed conventional practice in terms of yield and environmental effect. In most cases, higher manure fertilization in the zones with higher soil productivity and lower fertilization in zones with lower soil productivity showed the most favourable results.