Skipping alfalfa ‘summer slump’ irrigation has pros, cons

Skipping alfalfa ‘summer slump’ irrigation has pros, cons

Robert Glennon of the University of Arizona suggests that alfalfa farmers not irrigate the crop during the 'summer slump' period and instead sell or lease the water to cities. Skipping the irrigation has its pros and cons - depending on location, soils, pests, and salt buildup. Some growers cannot afford to skip the irrigation due to market demand, including equine hay sales.

Usable water – there’s seemingly not enough for life around the globe despite the many conservation efforts underway to save it and prolongued drought.

Four consecutive years of epic drought in California continues to take its toll on available water supplies for users including the food and fiber industries. A ‘down under’ drought in Australia has stretched for nearly two consecutive decades with no immediate relief in sight.

Finding better ways to manage global water supplies and shortages is the focus of water proponents around the world, including Robert Glennon of the University of Arizona (UA). Glennon is a UA Regents’ Professor and Morris K. Udall Professor of Law and Public Policy and the author of two water books.

On the farming side of water use, Glennon advocates that agriculture should voluntarily lease or sell 4 percent of its available water to cities for municipal and industrial uses. With the escalating drought in the West, Glennon’s viewpoints may not gain much favor with growers compared to wetter years.

In the June 6 issue of Western Farm Press, Glennon penned a guest commentary on his water vision. He suggested alfalfa growers skip the irrigation cycle during the ‘summer slump’ period in late July into August and send the water to cities.

He contends the late summer irrigation is a poor use of water as hot summer temperatures can increase plant water needs and decrease yields.

“A modest reallocation of water from farms to cities need not jeopardize rural communities’ vibrant futures,” Glennon professes.

Glennon suggests another option - a water trade out. In exchange for taking farmers’ water, cities would pay for the installation of higher efficiency irrigation systems on farms.

“It’s a win-win option,” Glennon said.

If further improvements in water conservation were achieved, Glennon says alfalfa farmers could grow the same amount of alfalfa but with a little less water.

Glennon will share his water outlook ideas in more detail Dec. 3 during the 2015 Western Alfalfa and Forage Symposium in Reno, Nev.

Production impact

Skipping an irrigation may not be a good idea for some growers who, for example, grow and sell summer hay for equine.

On the production side, what is the impact of skipping the late summer irrigation on the alfalfa crop, the stand, and growers? Western Farm Press asked three western university alfalfa specialists for their input.

Certainly saving water and related costs is one benefit, says Mike Ottman, University of Arizona Extension agronomist at Tucson. He says a pro or a con, depending on the grower and the soil, relates to harvesting the summer slump crop.

On one hand, the grower could skip the harvest since yields could be lower. On the other hand, the grower may still choose to harvest the ragged-looking alfalfa in the field. The latter decision would negate harvest savings.

On the yield side, Ottman said, “If irrigations were skipped for an entire cutting cycle in the summer, the amount of hay produced may be negligible unless significant rainfall occurs.”

Stand loss odds

Can alfalfa growers lose a stand from skipping irrigation? Ottman says stand loss normally does not occur from skipping irrigations for a few cutting cycles. However, stand loss can occur in sandier soils or soils with poor water infiltration where scalding can occur when irrigation is resumed.

A drawback from skipping the water could be an increase in the soil’s salt content. Also, net water savings could actually be reduced if more water is required in the subsequent irrigation, particularly in dry, cracked soil.

Ottman says water-stressed alfalfa can attract insects, including lygus and the potato leafhopper, which may require pesticide treatment(s) and costs. However, these pests may be present anyway. The grower could decide not to treatment pests in non-irrigated alfalfa.

In a water-short year, a grower with alfalfa and cotton could pass on a summer alfalfa irrigation, and deliver the water to the cotton instead. In the end, this would mean no net water savings but the flexibility to maintain cotton productivity.

Soil and ET

Dan Putnam, University of California, Davis statewide alfalfa and forage Extension specialist, agrees that late summer water reductions can reduce yields, depending on the soil type and evapotranspiration at the time.

“With soils with very high water holding capacity and deep water supplies, the cessation of irrigations may result in only minor yield penalties for one cut, perhaps two, or even three after the irrigations stop,” Putnam said.

On soil types with poor water-holding capacity and the lack of subsoil moisture, he says plants can more rapidly shift into induced summer dormancy; appearing brown and with little growth.”

If a grower applies 50 percent of the annual water required by the crop by stopping irrigations in mid-summer, Putnam says the grower is likely to receive greater than 50 percent of the annual yield. 

“This is because yield and quality are typically quite a bit higher during the early harvests (1st, 2nd, 3rd cut) versus later cuttings in the season,” Putnam said. “A ‘dry down strategy’ takes advantage of the early high water-use efficiencies to maximize yield and quality and economic return.”

Additionally, alfalfa has such deep roots and can be sustained by water applied months earlier, even after the irrigations stop.

Drought-based water cuts

This year, some California alfalfa growers have done this out of necessity due to the drought and limited water supplies – halting alfalfa irrigation during the last months of production (from late June or July through the fall) to transfer the water to orchards or urban uses.

Putnam said, “In a very real sense, alfalfa enables growers a higher degree of flexibility during drought periods compared with crops which cannot be sustained on less than full irrigation applications. This is why we say alfalfa is the best crop to have in a drought.”    

Alfalfa no water hog

Ayman Mostafa, UA area Extension agent at Phoenix, says alfalfa is falsely accused as a large water using crop. He says 100 percent of the alfalfa plant is harvested and usable, making its water use efficiency high, compared to head lettuce, cotton, almond, and grains where parts of the plant are harvested and the balance remains in the field.

Mostafa says year-long alfalfa production in Arizona and California requires 4-6 acre feet of water annually; a similar amount per unit to produce cotton, almonds, and vegetables.

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