Combat Drought Conditions With More Efficient Water Usage

Weather stations that measure evapotranspiration can be used to estimate the water needs of vegetable crops.  Photo credit: Michael Cahn

Weather stations that measure evapotranspiration can be used to estimate the water needs of vegetable crops. Photo credit: Michael Cahn

In the West, we are accustomed to having emergency plans for surviving earthquakes, floods, and wild fires. Unfortunately, droughts are also a recurring problem. The drought in 1976-77 was a major challenge for growers in California when the urban population was about 60% of the present population, and when there were fewer mandated water allocations for protecting aquatic habitats.

With 2013 being the driest year ever in recorded California history, and the state heading into 2014 with little cumulative rainfall and minimal snow pack in the mountains, the current drought may become as serious as in the 1970s. Confronting a season that could be as dry as 2013, many vegetable growers are wondering what they can do to prepare. Both short- and long-term strategies can help farming operations during drought years.

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Convert To Drip, Sprinklers
Some of the strategies that can be put into practice immediately to use water more efficiently are to convert acres to more efficient irrigation methods such as drip and sprinklers, improve irrigation scheduling, and adjust existing irrigation systems so that water is applied uniformly. Often, opportunities do exist to save water in vegetable production. A significant portion of water used to grow many short-season, seeded vegetables, such as lettuce, is used for germination.
By either carefully monitoring soil moisture during these first irrigations or using transplants, growers can often save considerable amounts of water.

Most Western states have evapotranspiration (ET) data available on the Internet. Estimating crop water use from historical ET data can help growers determine the minimal amount of water needed for crops and estimate the acres they can farm with a limited water supply. Daily ET data can be used to guide irrigation scheduling by estimating the amount of water to apply to meet crop needs. Additionally, soil moisture sensors and flow meters are important tools for fine-tuning irrigation schedules.

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Deficit irrigation is often used for tree crops to conserve water. For some vegetables, such as processing tomatoes, applying less water than the crop ET demands may result in minimal yield losses while for other vegetables, such as celery, deficit irrigating could cause dramatic losses in yield and quality. Many vegetables can tolerate dry soil conditions during specific development stages without significant reduction in yield, such as between establishment and flowering in tomatoes.

Head lettuce can also tolerate minimal water applications from after germination to leaf cupping. Encouraging deeper rooting by holding back on water after establishment, or through practices that improve soil tilth, can also help crops use water that percolates deeper into the soil profile.

The Salinity Issue
The lack of winter rainfall means that salinity may be an important issue for vegetable growers in 2014. Normally rainfall pushes salts that have built up near the soil surface downward. Many of the first vegetable crops planted this year will begin growing at higher levels of soil salinity, and growers may experience germination and stand establishment problems. Also, growers switching to ground water this year should consider that dissolved salts in well water may be significantly higher than the salts in their surface water supplies.

Many vegetables such as lettuce, carrots, and onions are sensitive to salts, and may need extra water to leach salts below the root zone and minimize yield impacts. However, leaching without knowing the salinity level of the soil could result in over-applying and wasting water or applying an insufficient amount to prevent yield losses. Monitoring the salinity of the soil and irrigation water periodically throughout the season can be a valuable tool for judging how much water is needed for leaching.

Over the long term, the vegetable industry will need to breed varieties that are increasingly tolerant to drought and salinity. Additionally, farmers will need to develop new water sources, such as using recycled water from urban areas, to supplement their regular water supplies. Irrigators will need to be better educated and trained, and the irrigation industry will need to develop improved equipment and tools that growers can use to irrigate more efficiently.

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