Crop rotational effects on soil structure, root development and yield formation of winter wheat

Winter wheat (Triticum aestivum L.) is one of the most important staple food crops worldwide and commonly grown in crop rotations to obtain high grain yields and overcome increased disease pressure which is caused by monoculture cultivation. However, based on the high economic advantages of wheat production, in several cases wheat is also grown after wheat (stubble wheat or monoculture). It is hypothesized that lower grain yield of wheat, grown after wheat is caused by differences in the root development of the plants, which might be triggered by changes in the soil structure or an infection with the fungus Gaeumannomyces graminis var. tritici (Ggt). This thesis investigated the effects of the crop rotational position of winter wheat on soil structure at the beginning of the growing season, possible differences in wheat biomass formation at this timepoint, as well as the effects on above-ground biomass formation, root development and nutrient acquisition during the growing season, a possible take-all occurrence, and, finally, wheat grain yield. The root development was investigated with destructive soil core sampling at two timepoints and with biweekly scans of minirhizotron tubes throughout the growing season. The third study further aimed to adapt an existing Convolutional neural network (CNN)-based segmentation method for high-throughput image analysis of minirhizotron images of wheat as well as to investigate a possible effect of the presence of the minirhizotron tubes in the soil environment on root development. The crop rotational position of winter wheat did not cause differences in soil structure in April and therefore was not related to differences in wheat biomass formation by this date. Root length density in subsoil at later growth stages was higher for winter wheat grown after oilseed rape compared to after winter wheat, which was independent of take-all infection and corresponded well to a higher biomass formation and finally a higher grain yield. The root development of winter wheat, especially in the subsoil, might thus be the key to understand biomass and yield formation of wheat in different crop rotational positions. The minirhizotron image analysis based on the adapted CNN showed that the presence of the minirhizotron tubes affect the root development only if the tubes are not installed with a good soil-tube contact, which can be achieved by slurrying. Further investigations are needed to identify processes, related to biomass formation of winter wheat cultivated after winter wheat pre-crop in detail and which properties of the pre-crops affect the root and overall biomass development of the subsequent crop. Possibly, research on the rhizosphere microbiome and the related processes, also in the early development phase of the plants, can present beneficial genera of bacteria which might be able to overcome wheat yield decline.

2025-02-21