A Dutch research group carried out a meta-analysis study on the tolerance of different types of berries to the shade produced by agrivoltaic systems. His work focused, in particular, on strawberries, blueberries, blackberries and black currants.

Meta-analysis consists of a statistical combination of results from multiple scientific research works focused on the same topic.

“This study provides the first yield response curves of individual berry crops to increased shade, also distinguishing between different radiation intensity environments,” the researchers said. “The response curves provide valuable information for the design of agrivoltaic systems and can help select optimal combinations of crops and panel density for different locations.”

The study began with 3.677 agronomic experiments, considering berry performance under at least two light levels. For their analysis, the scientists considered the entire spectrum of wavelengths of solar radiation, the main production season of the berry and temperatures.

“Radiation treatments are created with shade nets, natural foliage, or a vertical light gradient in a ladder-like vertical growing system,” they explained. “Radiation treatments created with closed impermeable covers, such as plastic tunnels or glass greenhouses, were excluded due to the insulation these materials offer.”

After applying the list of criteria, 22 scientific articles remained. From them, the scientists created individual observations, combining the year of publication, the crop variety and the relative shade rate (RSR). Through each observation, scientists were able to define the corresponding relative yield (RY), radiation intensity level (RIlev) and shadow type (ST).

“We fit a mixed-effects model to account for random differences between publications,” the scientists explained in their approach to data analysis. “The model response variable was relative performance, and we used a backward elimination process to determine significant fixed effects.”

Through this analysis, the scholars found that relative shading rate is a significant predictor of yield response, indicating that in most cases, low levels of shading are relatively less detrimental, or even beneficial, for berry yield than high levels of shade. “An exception to this is the response of strawberries with increasing yields to high rates of shade,” they emphasized. “Physiologically, this response is very unlikely and can probably be attributed to the limited number of data points with low shadow rates.”

Another finding was that there is a significant difference in crop yield response between environments with high and low radiation intensity. The analysis showed that yield losses as a result of shading are more substantial in low radiation intensity environments. “This suggests that successes in one region will not necessarily be sustained in another,” the group said.

“We conclude that, although classified as shade beneficial in previous literature, not all berries are equally shade tolerant,” they added. “While the yield of blueberries under high radiation intensities can benefit from up to 50% shade, other types of berries are better classified as shade tolerant, withstanding up to 35% shade without yield loss, but decreasing after".

They presented their findings in the study” Shade tolerance of berries for agrivoltaic systems: a meta-analysis ", published in Scientia Horticulturee . The group was made up of scientists from the Wageningen University and the Wageningen Research Foundation.

Relative performance response curves at low (blue line) and high (red line) radiation intensity levels
Image: Wageningen Plant Research, Scientia Hortícolae, CC BY 4.0 DEED