In Field Assessment on the Relationship between Photosynthetic Active Radiation (PAR) and Global Solar Radiation Transmittance through Discontinuous Canopies

Abstract

In many crop models, the process of radiation transmittance through the canopy is normally described as an exponential attenuation process (Beer's Law equation), which is assumed to be valid for canopies covering the ground with a random spatial distribution of leaves. However, for discontinuous canopies, where a distinctive row pattern of plant exists, there is a more complex situation because of the presence of gaps between individual plants. This must be accounted for when characterizing radiation relationships for these kinds of systems, in particular when short time-scales are of interest. Photosynthetically active radiation (PAR) transmittance (τPAR) is more commonly studied and reported than global solar radiation (Sg) transmittance (τSg). However, both PAR and Sg are important in radiative transfer sub-models used in plant growth simulation. In this work simultaneous measurements of τSg and τPAR under discontinuous canopies were performed, and the hourly changes in radiation transmittance for PAR and global solar radiation were characterized. Two methods were assessed to transform between τSg and τPAR. The two methods yielded similar results for low values of transmittance, but disagreement occurred for higher values of transmittance. The method based on a fixed value for the ratio of extinction coefficients for PAR and Sg outperformed the method based on a linear relationship between τPAR and τSg with average relative errors (RE) of 7.97% vs. 13.29% and 2.84% vs. 7.77% for hourly and daily time-scale, respectively.

Balanço de radiação de copas de cafeeiros em renques e suas relações com radiação solar global e saldo de radiação de gramado

“…Com a redução da área foliar e, concomitantemente, do autossombreamento das folhas, tem-se acréscimos nos valores do coeficiente angular "a", com bons ajustes para todas as condições de AF, de acordo com valores de R 2 (Tabela 2). Na figura 7 são observados bons ajustes exponenciais negativos desses coeficientes angulares com a variação da área foliar média por planta, o que pode explicar o bom desempenho de modelos matemáticos embasados na Lei de Beer, empregados tanto na estimativa da interceptação de energia radiante por copa de arbóreas (Angelocci et al, 2008;Oyarzún et al, 2011) (Silva et al, 2008).…”

Protected Fresh Grapefruit Cultivation Systems: Antipsyllid Screen Effects on Plant Growth and Leaf Transpiration, Vapor Pressure Deficit, and Nutrition

“…As tree canopy and LAI increased, the proportion of PAR intercepted by photosynthetically active canopy elements also increased. This relationship is often described by biophysical models derived from the Lambert-Beer law (Annandale et al, 2004;Oyarzun et al, 2007Oyarzun et al, , 2011. In general, PAR interception by a fruit tree foliage increases exponentially with increasing canopy width and LAI.…”

Rain Cover and Netting Materials Differentially Affect Fruit Yield and Quality Traits in Two Highbush Blueberry Cultivars via Changes in Sunlight and Temperature Conditions

“…This demonstrates that, when these types of covers are used, the PAR reaching the soil surface is lower in the sections closest to the inter-row. Based on discontinuous canopy, this indicates that the plants grown under these covers would present greater uptake of PPFD through the canopy, which is directly dependent on the increase in LAI [26]. In addition to light interception, blueberry yield is also determined by the efficiency of converting light into biomass by the plant, which largely depends on the photosynthetic capacity of the leaves [27].…”