Quantifying the effects of light quantity and the red: far-red ratio on morphology and physiology of intercropped soybean
Plant Physiology
Final Report Abstract
This project focused on the morphological and physiological response of intercropped soybean. Soybean is often grown in association with a taller species, mainly maize, which results in a strong competition for light. This decreases not only the quantity of available light, but at the same time changes the spectral ratio of red to far-red radiation which generally induces shade adaptations in plants aiming at an increased light interception. Finally, the degree of light competition and the induced plant responses will influence the productivity of the shaded crop. Therefore, the first aim of this project was (i) to experimentally create a gradient of light competition for soybean, and (ii) to measure the induced response in morphology and physiology and the resulting final yield. Further, we included two soybean cultivars in the experiment to evaluate genetic variability in these responses. We conducted a field experiment for two years at the experimental station ‘Ihinger Hof' of the University of Hohenheim in Southwestern Germany (48°44’N, 8°55’E). The gradient in light competition was created by planting maize and soybean in alternating strips. Measurements were conducted in several rows across the maize and soybean strip comprising biweekly architectural measurements (dimensions and orientation of individual organs) and continuous measurements of photosynthetically active radiation (PAR) and red to far-red ratio above the soybean canopy. At final harvest, yield and yield components were determined in all individual rows across the strips of maize and soybean. The results showed that the shaded soybean plants increased mainly their plant height by internode and to a minor extent petiole elongation, and the leaf area was slightly increased. These responses clearly aimed at a higher light interception. Shaded soybean plants had a lower maximum assimilation rate, but lower dark respiration and light compensation point. Maize plants did only exhibit differences in plant height across the strip, but leaf area index was not affected. The intercropping yield was only comparable to monocropping in one year, on the other year lodging severely reduced the yield of the intercropped soybean. Based on the acquired data, the hourly light availability was satisfactorily simulated with a functional-structural plant model (FSPM). Next, the observed response to the light regime will be added to gain process-understanding of these responses, i.e. the quantitative response to changes in light quantity and red to far-red ratio. This finally enables to adapt inter-cropping systems with the aim to optimize productivity including both the temporal and spatial arrangement of crops and the selection of specific cultivar characteristics.
Publications
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(2018): Functional-structural plant model for testing the effect of maize architecture on hourly light distribution in strip-intercropping systems. 6th International Symposium on Plant Growth Modeling, Simulation, Visualization and Applications (PMA), Hefei, China, pp. 115-119
Munz, S., Henke, M., Graeff-Hönninger, S.
