Effects of red and blue light treatment on water, microclimate, soil and tomato crops in California

Recent advances in agrivoltaic systems (AVSs) have revived interest in understanding the effects of not only light intensity but also different light spectra on plants and overall land productivity, with research showing plant carbon assimilation being more efficient under red light, while the more energetic blue light would be more effective for producing solar electricity. AVSs are highly efficient in harvesting solar radiation for the cogeneration of food and solar electricity, thus resulting in higher land productivity, compared to single-use alternatives, i.e., agriculture or utility-scale solar. This is particularly advantageous in arid and semi-arid areas with abundant sun and limited land and water. The question becomes: how much light and what particular spectra of light are more efficient for food and for energy conversion, and how can any light treatment impact water, soil, microclimate and plant productivity? This study explores the potentials of spectrally selective PV panels by testing the performance of field grown processing tomato with the focus on red and blue light treatments. The study evaluates crop productivity and water savings by monitoring microclimate, soil, and plant responses under two specific wavelength patterns (red and blue filters) compared to the full unfiltered light spectrum (control). The red and blue treatments, applied on processing tomatoes in Yolo County (California), yielded 67 % and 58 % of the control, respectively. However, changes in the microclimate - particularly the reduction in solar radiation -resulted in a significant decrease in evapotranspiration. Consequently, the potential water use efficiency (WUE) for the blue and red light treatments compared to the control was improved by 10 % and 13 %, respectively. Overall, our study suggests that benefits from renewable energy and reduced water usage could offset yield reductions, making spectrally selective AVSs a potentially viable and sustainable land-use option, especially in water-scarce regions.