Abstract
Plant growth is directly related to levels of photosynthetic photon flux density, Qp. The improvement of plant-growth models therefore requires accurate estimations of the Qp parameter that is often indirectly calculated on the basis of its relationship with solar irradiation, RS, due to the scarcity of ground measurements of photosynthetic photon flux density. In this experimental campaign in Burgos, Spain, between April 2019 and January 2020, an average value of the Qp/Rs ratio is determined on the basis of measurements at ten-minute intervals. The most influential factor in the Qp/Rs ratio, over and above any daily or seasonal pattern, is the existence of overcast sky conditions. The CIE standard sky classification can be used to establish an unequivocal characterization of the cloudiness conditions of homogeneous skies. In this study, the relation between the CIE standard sky type and Qp/Rs is investigated. Its conclusions were that the Qp/Rs values, the average of which was 1.93±0.15 μmol·J−1, presented statistically significant differences for each CIE standard sky type. The overcast sky types presented the highest values of the ratio, while the clear sky categories presented the lowest and most dispersed values. During the experimental campaign, only two exceptions were noted for covered and partial covered sky-type categories, respectively, sky types 5 and 9. Their values were closer to those of categories classified as clear sky according to the CIE standard. Both categories presented high uniformity in terms of illumination.
Highlights
The portion of the solar spectrum that plant biochemical processes use in photosynthesis for converting light energy into biomass is a composite of wavelengths between 400 and 700 nm that are diffused within the visible light spectrum band (380–780 nm)
The analysis of photosynthetic photon flux density to broadband solar radiation ratios registered between April 2019 and January 2020 in Burgos, Spain, at ten-minute intervals, has shown a representative dependency on the sky type conditions classified by CIE taxonomy
The higher values of the Qp /Rs ratio were for overcast sky types, while the values were lower and more dispersed under clear sky conditions
Summary
The portion of the solar spectrum that plant biochemical processes use in photosynthesis for converting light energy into biomass is a composite of wavelengths between 400 and 700 nm that are diffused within the visible light spectrum band (380–780 nm). Solar elevation has no significant effect on PAR/Rs when greater than 10◦ [18,19] The variations of this ratio with sky conditions have been studied to develop weather-dependent functions. Most studies have concluded that the PAR/Rs ratio presents its highest values for cloud-covered skies [20,21] This fact is attributable to cloud-related absorption and diffusion of solar radiation across different regions of the spectrum. Experimental data on horizontal solar global irradiation, R ; photon photosynthetic flux density, Q ; and, the CIE standard classification for homogeneous skies; collected through experimental sky scanner measurements, were available for this work. Standard classification in Burgos during thebeexperimental as2.well quality filterssky applied to the experimental data will described incampaign
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
