Contrasting yield responses at varying levels of shade suggest different suitability of crops for dual land-use systems. A meta-analysis.

Moritz Laub,Sabine Zikeli,Lisa Pataczek,Arndt Feuerbacher,Petra Högy

doi:10.31220/agrirxiv.2021.00099

Abstract

Abstract Despite the large body of research studying crop growth parameters, there is still a lack of systematic assessments on how harvestable yields of different crop types respond to varying levels of shading. However, with the advent of agrivoltaic (AV) systems, a technology that combines energy and food production, and the new focus on agroforestry (AF), shade tolerance is becoming an important parameter for crop production systems. To address this research gap, a meta-analysis with data from two experimental approaches (intercropping and artificial shading with cloths, nets or solar panels) was performed to quantitatively assess the susceptibility of different temperate crop types to increasing levels of shading. Crop type specific yield response curves were estimated as a function of reduction in solar radiation (RSR), by estimating relative crop yields compared to the unshaded controls. Only studies that reported RSR and crop yield per area in temperate and subtropical areas were included. Using a random slope effect for each study, the specific variance components were accounted for. The results suggested a nonlinear relationship between achieved crop yields and RSR for all crop types. Most crops tolerate RSR up to 15%, showing a less than proportionate yield decline. However, significant differences between the response curves of different crop types existed: Berries, fruits and fruity vegetables benefited from shading up to RSR of 30%. Forages, leafy vegetables, tubers/root crops and C3 cereals showed initially less than proportionate crop yield loss. In contrast, maize and grain legumes experienced strong crop yield losses even at low RSR levels. The results provide first indicators for differences in crop type suitability to shading, and thus for AV and AF systems. Detailed yield response curves, as provided in this study, are valuable tools to optimize the output of annual crop components in AV and AF systems.

Highlights

With its goal to reach net-zero greenhouse gas emissions by 2050 (European Commission 2018), the European Union (EU) has recently made another clear commitment towards renewable energies
There is no evidence of a significant difference in the response of yield to reduction in solar radiation (RSR) between intercropping and shading-only experiments, or whether cloths, PV panels or nets were used for shading
We presented the results of a meta-regression by a mixed effects model, to estimate the susceptibility of different crop types to shading

Summary

Introduction

With its goal to reach net-zero greenhouse gas emissions by 2050 (European Commission 2018), the European Union (EU) has recently made another clear commitment towards renewable energies. One of the most cost-effective technologies, ground-mounted photovoltaic (GM-PV) systems, directly competes for land with agricultural production (Schindele et al 2020). Agrivoltaic (AV) systems enable the combination of PV and agricultural production on the same area of land (Dinesh and Pearce 2016), e.g., by elevating the PV panels to heights greater than five meter (Fig. 1). This allows for all agricultural activities to be performed in AV systems, maintaining most of the crop growing area. While AV systems come at higher costs compared to GM-PV, they may still allow for reasonable agricultural yields (Schindele et al 2020). Defining and delimiting AV in comparison to GM-PV was one reason to establish the specification (“pre-standard”) 91434 for AV systems in Germany

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