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Denise Neilsen explains how an atmometer is used in a cherry irrigation experiment at the Summerland research center in British Columbia.

Denise Neilsen explains how an atmometer is used in a cherry irrigation experiment at the Summerland research center in British Columbia.

The timing of irrigation can impact the growth of a cherry tree and the quality of the fruit, research in British Columbia, Canada ­suggests.

Drs. Gerry and Denise Neilsen, scientists at the Pacific Agri-Food Research Centre at Summerland, are conducting an experiment with sixth-leaf Skeena and Cristalina cherries on Gisela 6 rootstocks using a drip ­irrigation system and an atmometer to schedule the ­irrigation.

The atmometer simulates the rate of evapotranspiration in the block so that the irrigation controller can be programmed to automatically open and shut the valves to apply water as necessary. The crop coefficient used is 1.2 during the growing season but drops to 0.8 after harvest. The block is irrigated until October.

The Neilsens are comparing two irrigation treatments in a research plot with very sandy soil. One set of trees of each variety is irrigated once every two days. The other set is irrigated four times daily, but receives the same ­volume of water overall as the first treatment.

Gerry said the trees irrigated only once every two days are significantly smaller than the trees watered more ­frequently.

“It astonished us, because every two days seems not too bad,” he said. “Even though these are on Gisela 6, which is not as dwarfing as Gisela 5 or 3, they’re still very sensitive to water stress. Pulsed irrigation seems to have benefitted the initial growth. Even though they are dwarfing trees, you want them to establish quickly.”

Fruit quality

The trees are now in their sixth leaf. Last season, the Neilsens began to compare fruit from the two treatments and found that cherries from the less frequently irrigated trees have higher sugar levels, lower acid levels, darker color, and lower stem-pull force, suggesting accelerated maturity. “Those are all indications that the fruit development is stimulated by water stress,” Gerry said. But the cherries were also smaller.

“It’s interesting that when they’re stressed, you end up with more sugar,” he added. “You would not think that’s the case.”

The Neilsens will continue the study in order to gain a better understanding of how water stress affects fruit quality.