Quantifying the effects of light quantity and the red: far-red ratio on morphology and physiology of intercropped soybean

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Agricultural systems including simultaneously more than one crop (intercropping) are regarded as a very important aspect within the global challenge of sustainable intensification of agriculture. For example, intercropping of maize and legumes is very common. In these systems shading by the larger maize crop modifies considerably the light quantity and as well the light quality - of particular interest the red: far-red ratio - for the legume crop, e.g. soybean. However, the effects of these changes on the productivity of these systems have been poorly understood. Therefore, understanding and quantifying these effects will facilitate to identify relevant morphological and physiological cultivar characteristics of soybean responsible for a high productivity. To achieve these objectives, this project will quantify the effect of light quantity and the red: far-red ratio on morphology and physiology and finally biomass and yield of soybean. A field experiment with maize and soybean intercropped in wide strips - to create a large gradient of light quantity and the red: far-red ratio - will be conducted, in which light quantity, the red: far-red ratio, plant architecture, photosynthesis, biomass and yield will be determined over the created gradient. Then, a recently developed functional-structural plant model will be parameterized and calibrated to account for the measured effects of light quantity and the red: far-red ratio to understand the basic processes involved in light competition. Finally, based on the new knowledge about the processes and the developed plant model, optimum cultivar characteristics can be identified to guide breeding programs. And, the potential productivity of intercropping systems with maize and soybean can be estimated. Moreover, the developed methodological approach will be applicable to other species and intercropping systems.