Ground-Based Thermal Imaging for Assessing Crop Water Status in Grapevines over a Growing Season

Zheng Zhou,Sushma Thapa,Geraldine Diverres,Qin Zhang,Chenchen Kang,Manoj Karkee,Markus Keller

doi:10.3390/agronomy12020322

Zheng Zhou, Sushma Thapa + Show 5 more

Open Access

https://doi.org/10.3390/agronomy12020322

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Abstract

The quality of wine grapes in dry climates greatly depends on utilizing optimal amounts of irrigation water during the growing season. Robust and accurate techniques are essential for assessing crop water status in grapevines so that both over-irrigation and excessive water deficits can be avoided. This study proposes a robust strategy to assess crop water status in grapevines. Experiments were performed on Riesling grapevines (Vitis vinfera L.) planted in rows oriented north–south and subjected to three irrigation regimes in a vineyard maintained at an experimental farm in southeastern Washington, USA. Thermal and red–green–blue (RGB) images were acquired during the growing season, using a thermal imaging sensor and digital camera installed on a ground-based platform such that both cameras were oriented orthogonally to the crop canopy. A custom-developed algorithm was created to automatically derive canopy temperature (Tc) and calculate crop water stress index (CWSI) from the acquired thermal-RGB images. The relationship between leaf water potential (Ψleaf) and CWSI was investigated. The results revealed that the proposed algorithm combining thermal and RGB images to determine CWSI can be used for assessing crop water status of grapevines. There was a correlation between CWSI and Ψleaf with an R-squared value of 0.67 for the measurements in the growing season. It was also found that CWSI from the shaded (east) side of the canopy achieved a better correlation with Ψleaf compared to that from the sunlit (west) side around solar noon. The created algorithm allowed real-time assessment of crop water status in commercial vineyards and may be used in decision support systems for grapevine irrigation management.

Highlights

Irrigated agriculture is the biggest consumer of freshwater in arid and semi-arid areas, with a share of 70–80% of the total consumption
The rectangular Region of interest (ROI) was set in the canopy region of the masked thermal image (Figure 3d) for further analysis and crop water stress index (CWSI) calculation
Canopy temperatures in the same ROIs were manually extracted from thermal imaging, with visual inspection to validate the Tc determination

Summary

Introduction

Irrigated agriculture is the biggest consumer of freshwater in arid and semi-arid areas, with a share of 70–80% of the total consumption. Many vineyards are located in semi-arid areas which require precise regulation of the water supply [1] Since both the yield and quality of berries are sensitive to changes in water availability to vines [2], precise and robust methods to accurately and precisely detect grapevine water status are becoming increasingly important in commercial vineyards. Traditional measurement approaches, such as pressure chambers, used to measure leaf water potential (Ψleaf), are time-consuming and require skilled operators.

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