Quantifying lower crop radiation availability in strip intercropping systems via UAV-derived canopy structural models

Abstract

• UAV-derived canopy model quantified radiation availability of intercropped soybean. • Shadow fraction method was developed to calculate direct, diffuse radiation and RUE. • RUE of intercropped soybean was higher than that in monoculture. • Fraction of diffuse in intercropping was slightly lower than that in monoculture. • Other factors leading to the higher RUE of soybean in intercropping systems. Shading is an unavoidable phenomenon in strip intercropping systems for lower crops, which affects the amount and component of solar radiation, and thus the radiation use efficiency (RUE). The higher crop is usually treated as a homogeneous block instead of the actual canopy structure to calculate lower crop radiation availability (block-based method, BM), which underestimates the amount of light passing through gaps in the canopy. Here we proposed a new shadow fraction method (SFM) to separately quantify direct and diffuse radiation on lower crops. The SFM considered shadow fraction dynamic and view factor within a day, which was calculated based on UAV-derived canopy structural models. To test this method, UAV images and crop data were collected from a maize-soybean intercropping experiment with six planting configurations. For daily total radiation, as the width of the soybean strip decreased from 3.8 m to 1.6 m, the relative difference between BM and SFM increased from about 11.10% to 20.36%. Accordingly, the RUE of soybean calculated by the SFM was 0.2–0.3 g/MJ lower than the BM. Consistent with previous studies, the RUE of soybean in strip intercropping systems (1.36–1.61 g/MJ) calculated by the SFM was higher than that in monoculture (0.98 g/MJ). The higher RUE was usually attributed to the increasing fraction of diffuse in strip intercropping systems. However, SFM showed that the fraction of diffuse on intercropped soybean (ranged from 37.42% to 38.58%) was slightly lower than that in monoculture (39.48%), implying that other factors, such as light intensity and quality, may have an impact on soybean performance and warrant further investigation. The SFM was theoretically more accurate than BM as it considered the actual 3D canopy structure. This method can enhance the understanding of light distribution and use efficiency in intercropping systems, which can be integrated with crop growth models or functional structural plant models to optimize intercropping configurations for improved resource use efficiency.

Plant phenotyping relevance

UAV由来の3Dキャノピー構造モデルを用いて、下層作物の光環境を推定する新しいshadow fraction法を開発・検証しており、植物キャノピー構造と放射利用効率の定量化が研究の中心である。

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