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Changing cropping patterns spawning new irrigation studies

Dwindling water supplies and changing cropping patterns have growers rethinking their irrigation strategies on the West Side of California’s San Joaquin Valley. The fast farming area was once planted in cotton, melons and tomatoes as far as the eye can see. But as growers look to improve returns they are transitioning to crops that can offer consistently higher returns.

This change has come with drastically reduced surface water deliveries.

“We continue to have a dwindling supply of water on the West Side,” Dan Munk, an irrigation farm advisor with the UC Cooperative Extension in Fresno County, told growers at an irrigation field day at the West Side Research and Extension Center (WREC). “On the other hand, we are getting good prices and strong demand for our crops so we need to maximize our irrigation efficiency.”

Jim Ayars with the USDA’s Agricultural Research Service in Parlier is conducting replicated field trials on fall and winter vegetables grown on Panoche clay loam soil at WREC to develop crop coefficients specific to the West Side for many of the newer crops. These crop coefficients will help growers develop climate-based irrigation strategies to maximum use of available surface water on flood, subsurface drip and surface drip systems.

Tulare County UCCE Farm Advisor Carol Frate said growers are converting more acreage to corn in her area to capitalize on higher returns, but there is little research available on maximizing water use efficiency on corn for West Side producers.

Frate is also developing irrigation recommendations to determine if growers can get by with fewer irrigations when growing corn for grain or silage. She noted, however, that previous research indicates delayed irrigations that create stress in the corn plant and should be avoided at all stages of crop development.

“There is no good time to make your crop suffer if you are growing corn,” Frate said. “There is no safe time to stress corn.”

However growers may be able to get by with one or two fewer irrigations, particularly on silage corn, without hurting yields, as long as the deficit is timed to avoid crop stress.

During the vegetative stage, prior to tasseling, corn is most susceptible to the effects of water or nutrient stress, and withholding irrigations can have a significant impact on yield. Silking, when the reproductive stage begins, is also a critical time to avoid water or nutrient stress.

“The most critical time for grain yields is two weeks before and after silking,” Frate said. “That is also important for silage production because it will affect grain production and energy content in the silage.”

However, Frate said that growers may be able to save water on corn by withholding one or perhaps two irrigations once dent appears, typically about 35 to 42 days after silking and as the plant approaches black layer.

Frate said corn no longer uses resources once a black layer is formed at the tip of the kernel, and irrigation can cease from that point.

“If you have black layer you do not need to irrigate,” Frate said. “Once this happens the plant is going to die down, so if you have water in the soil to carry you to black line, that’s all you are going to need.”

Corn has a fibrous root system and only uses water in the top two to three feet of the soil profile. As a result, Frate said more frequent, lower volume irrigations are best for corn.

“So if you are a cotton grower who is now growing corn, you do not want to do those deep soakings that work so well in cotton. Lower volume, more frequent irrigations are better,” she said.

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