In an irrigation trial that lasted several years, strawberry and blackberry crops in Northern California were given different amounts of water to determine how to maximize water use efficiency without affecting yield.
Farm advisors found that deficit watering did not necessarily reduce the size of the fruit or sugar content by much, but it did impact taste — in a positive way.
Aziz Baameur is a retired small farms advisor with the University of California’s Department of Agriculture and Natural Resources (UCANR) who worked with specialty crops and small growers in Santa Clara County.
“Our initial focus was to see if current practices with the amount of water used is efficient, how to quantify it, and how do we research it if we think it could be done better,” he said.
Plants in different areas use different quantities of water to stay alive. The universal principle is transpiration, and Baameur used crop co-efficiency factors to calculate how much water plants lose depending on environmental factors, and how to replace it.
“We used a network of weather stations within the state, the California Irrigation Management Information System, which gives us information on how much water was lost in the previous few days, so I can plan my irrigation for the next few days,” he explained.
The trial involved four types of water applications.:
• Normal irrigation in which 100 percent of the lost water was replaced. This also functioned as the base measurement level for the trial.
• Deficit irrigation levels in which they went with 25 percent lower water replacement, watering the plants at only 75 percent of their water needs.
• 50 percent lower water, in which the berry plants were given half of what they needed.
• Surplus irrigation, in which 125 percent of the water needed was applied.
The surplus treatment was to help those farmers who like to use more water, and to see if it actually helped the fruits in terms of production and yield.
What they found was that yield did not vary as much as they expected. Even at 50 percent deficit watering, Baameur expected to lose half his yield but while there was some loss, it wasn’t significant.
So he said as long as growers stay within a reasonable range, production figures will not be impacted.
“Fruit size changed a little but not drastically,” he noted. “It was smaller by a few percent.”
The berries were harvested once a week and tested for sugar content and pH levels. He did not see significant differences in these measurements for the four different levels of watering, but there was a noticeable difference in taste.
“We took the fruit to farmers’ markets and asked people to taste the berries, look at texture and appearance, and give us their impression,” Baameur said.
Many folks responded that they liked the 50 percent deficit watered berries more than the 125 percent level fruits, but others said they found them to be fairly similar.
“So this tells you, even with reduced water, the fruits were not shabby looking,” he said. “In terms of texture and flavor, the 50 percent level fruit had better texture and flavor than the rest although the others were fine, but these came out a little higher.”