Variability of Biomass Production and of N Status in Plants
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.
Basic prerequisite for a site specific plant production is to identify homogenous sites in a heterogeneous field. For that purpose several aids are available: yield maps of several years, soil maps, nutrient maps, information about slope inclination and exposure, aerial views, remote sensing etc.. Presumably a ranking of these sites based on yield, however, is not constant during any period of time because the yield is affected by the weather. Thus e. g. locations with lower usable field capacity (ufc) possess a higher yield potential in very damp years due to better draining than locations which tend towards water surplus caused by insufficient draining of gravitational water. Whereas in dry years the plants on locations with low ufc suffer very soon from water deficit, so that the yields turn out to be lower there (comp. Cluster 1 in fig. 1)
Therefore some further information besides the temporarily constant parameters has to be gathered for a site specific plant cultivation optimised in small fields - particularly for the nitrogen fertilisation, but also for the herbicide and fungicide application. These items of information reflect the yearly specific conditions. The two factors "site" and "yearly weather" essentially determine the status of the plants besides the management measures. Thus the plant itself can be regarded as a suitable indicator for the interaction of the respective environmental conditions.
In the past large-scale plant analyses were necessary for the quantitative assessment of a plant stand. To get along with without them in the future, therefore a touchless procedure for the plant appraisal is to be further developed in this subproject. Thus the information of an optic rating on the N status and the biomass production of the stand is of special interest.
In numerous trials of the Chair of Agronomy and Plant Breeding of the Technische Universität München an optimum N uptake curve of winter wheat to gain highest yields was found at the research station Roggenstein and at other sites (fig. 2).
As a function of the yield potential of a location the values defined for the N uptake of a plant stand at particular growth stages are to be kept. With the touchless procedure deviations of the actual N uptake from the requested one are to be diagnosed quantitatively and the two curves (actual and target uptake) are to be made congruent by putting the corresponding fertiliser amount.
Besides, current activities at the Chair deal with the optimum N uptake curve for the crop maize. The measure is also to be adapted to this crop. At a later date, an appraisal of this procedure is also intended in other cereal species and potatoes. Thus the superordinate goal of the subproject is a reasonable application of a site specific nitrogen fertilisation.
The opto-sensoric assessment relies on the measuring of reflection of the plant stand with a 2-channel spectral sensor system (fig. 3).
shows a course of the reflection in the range of wavelength of the visible
and the near infrared light, which is characteristic for plant stands. Such
measuring signatures as well as their mathematic processing allow to draw
conclusions from the condition of the stand. But the measurement is always
affected by disruptive elements (radiation geometry, lighting conditions,
characteristics of the crop, soil colour etc.), which must be recorded and,
if possible computationally eliminated.
You can reach the publications to this subproject here.