In order to realise a site-specific nitrogen fertilisation optimised for small fields, heterogeneous fields are subdivided into homogeneous areas which are cultivated individually. However, due to the interaction between the individual site and the climatic conditions it is exposed to in the course of the year, such a subdivision cannot be regarded as constant over several years and should therefore not rely on yield maps and soil differences only. Rather, it is more important to consider the differences in current growth and nutrition status of the plant population which do not necessarily correlate with the differences shown in soil and yield maps.
Destructive methods (soil and plant analyses) to identify homogeneous subdivisions are immensely labour and cost intensive when applied to large areas, they are therefore not suitable for this purpose. Therefore, this section of the project is intended to further develop and improve non-destructive procedures. For that purpose biennial field trials are being set up on sites with different yield potentials for winter wheat and maize. In these field trials, the cultivar, the N amount and, with maize also the seed rate, are varied. At various growth stages optical measurements are carried out, and, simultaneously, plant samples are taken and analysed. In this way the interaction is established between the spectral properties of the plant crop and its main parameters for biomass production and N uptake. Based on these analyses, a site-specific nitrogen fertilisation concept is to be designed for crops of different development and nutrition stages. Based on both the optical measurements and the empirical knowledge of the site, the aim is to gain a clear indication of nitrogen fertilisation at decisive growth stages.