Using MicaSense Altum to Monitor Water Stress in a Kiwi Orchard.

A Chilean company decided to test whether an aerial thermal sensor could help detect water deficit in kiwis through the CWSI (water stress index.)
NutriGis team with drone
nutriGIS team getting ready to fly over the kiwi orchard with the Matrice 200 and the MicaSense Altum.

Chile is the first biggest exporter of kiwis in the Americas and the fourth worldwide. To supply both the internal and external demand, the country has a total of 8,700 hectares planted, 37.7% of which are in the O’Higgins Region.

However, in recent years the consequences of climate change have become a threat to kiwi production and the country’s commercial well-being. An uninterrupted annual rainfall deficit has prevailed in central Chile since 2010, with the O’Higgins Region being one of the most affected areas.

In 2019 the region experienced the driest winter of the last 60 years. The municipality of San Fernando, located within the O’Higgins region, presented a 65% rainfall deficit with only 67.60 mm of rainfall when the normal is 126.60 mm.

Due to these prolonged dry conditions and other effects of climate change, farmers in Chile are looking for ways to optimize their use of water while minimizing the impact of drought on kiwi production. nutriGIS, a Chilean company that provides engineering services and technological solutions for agriculture, decided to test whether an aerial thermal sensor could help detect water deficit in kiwis through the CWSI (water stress index.)

The CWSI index measures the transpiration rate of a crop on a scale from 0 to 1, by estimating the canopy temperature and the vapor pressure deficit. When the temperature of the leaf exceeds the air temperature by 4 to 6 ° C, the resulting number is closer to 1 and the plant is determined to be under water stress.

Equipped with the MicaSense Altum and the Matrice 200, the nutriGIS team flew over a kiwi orchard (Hayward variety) in San Fernando in November 2019.

For comparison, nutriGIS also used a Scholander pressure bomb to measure the water potential of plant tissues. The use of a Scholander pressure bomb to measure water potential is a widely known method to establish the water status of plants and it is currently used to estimate water conditions in kiwis. In this particular case, nutriGIS selected thirty leaves from ten randomly chosen trees to test in the Scholander bomb.

By analyzing the images captured with the MicaSense Altum and comparing them with the xylem water potential obtained with the Scholander bomb, two zones, “Zone 1” of low stress and “Zone 0” of high stress, were identified.

The team also established a correlation between the data captured with the Altum thermal band and the water potential obtained with the Scholander bomb, which led them to conclude that Altum is a powerful tool for assessing water stress.

Table
Water potential data in kiwi leaves in correlation to stress zones.

The use of a thermal sensor like the MicaSense Altum allows growers to more accurately detect cases of water stress in kiwis. Instead of using a sample to generalize results, the whole field can be mapped and individual trees under water stress can be identified. With Altum, growers can not only deal with the impacts of climate change but also plan water use strategies at the tree level.

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