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Limited Irrigation Farming

Monday, January 1, 2001
filed under: Irrigation/Water Use

Limited Irrigation Farming

Less water, higher pumping costs has producers using water more strategically

Less water is becoming available for irrigation from the Ogallala Aquifer, and the rising cost of energy has made pumping water more expensive. Natural gas, widely used for irrigation, has about doubled in price over the past year. Thus, more producers in the High Plains are turning to limited (some would call strategic) irrigation during the growing season, watering crops when they need water most.

The Ogallala Aquifer sits beneath eight states in the High Plains, including much of Nebraska, Texas, and Kansas, as well as Colorado, New Mexico, Oklahoma, South Dakota, and Wyoming. One of the largest bodies of freshwater in the world, the Ogallala (also referred to as the High Plains Aquifer) is estimated to hold over one quadrillion gallons of water, a volume that would cover all of the 50 states in more than one and one-half feet of water, according to biologist Steve Overmann, Southeast Missouri State University. Much of the water in this aquifer is the remains of melt water from glaciers of the last ice age, and it’s estimated that at least 6,000 years were required to fill it.

It has served as a source of water for irrigation in the High Plains for over 50 years. But the water supply is slowly dwindling, as water recharge has not kept pace with water usage. Nearly 200,000 wells are withdrawing water from the High Plains Aquifer, according to Overmann, and estimates are that withdrawal rates are 10 to 50 times greater than recharge rates. In some areas, the water table has dropped 100 to 200 feet as a result of overdrafting of the aquifer.

Stan Murphy, district manager for the Plains and East Cheyenne Groundwater Management Districts, Burlington, CO, says that wells in parts of the districts he oversees are falling at a rate of one half to one foot per year. One well east of Burlington measured once a month since 1964 has dropped 37 feet in 33 years.

The Ogallala will have enough water to sustain municipal use, but eventually its draw-down may make irrigation prohibitive, unless other water sources are tapped.

A variety of approaches have been adopted over the years to prolong the longevity and effectiveness of the aquifer for irrigation, including permit restrictions, metered water withdrawl, using more efficient irrigation methods and technology, and scheduling irrigation according to crop needs, soil water depletion, and water availability.

To a certain extent, Mother Nature is doing a natural limitation. This past year a lot of irrigators had to renozzle sprinklers one, two, three, as many as four times throughout the irrigation season,” says Murphy. “As the water table went down, their gallons per minute went down, and so they had to operate sprinklers using lower pressure systems.”

Ron Meyer, Colorado State University area extension agent, Burlington, CO, says some producers are growing several crops in an irrigation circle—corn and sunflower, for example, watering the soil profile at planting, then at critical growth stages (see table). The critical yield period for sunflower generally occurs 20 days before and after flowering.

Some may irrigate sunflower only before planting. The sunflower plant is drought tolerant and has an extensive, heavily branched root system, which permits it to extract more deep soil moisture than corn roots. For this reason, preplant irrigations can have a longer benefit to sunflower than other crops, according to the Texas Agricultural Extension Service. Short periods of drought may not greatly reduce seed yield, because the crop is less stressed due to its large root volume.

“There are some guys that start the growing season with 600 gallons per minute of irrigation water in their well, and by August, are pumping only 400 gallons per minute, because the aquifer drops during the summer and it affects well performance. It would be optimal to see it at 700 to 800 gallons per minute or more, but when it falls under 600, they have to plant a drought-tolerant crop, and sunflower fits well into that,” says CSU’s Meyer. “You can produce good yields with limited irrigation of sunflower, which doesn’t like wet feet.”

One of the first lessons for new sunflower producers who irrigate, says Meyer, is that sunflower needs less irrigation than corn. Many producers who irrigate sunflower will generally apply two inches of water before planting, then another two inches at the bud stage. “It can depend on the weather. When it’s dry like the 2000 growing season, irrigating with three inches of water would be better,” says Meyer.

Ridge Till Compliments Limited Irrigation

Like many producers who irrigate, Dale Hansen has adopted technology over the years that has made irrigating his crops more efficient. From the 1970s to early 1990s, the Burlington producer converted from using surface irrigation with aluminum gated piping to center pivot sprinkler-irrigation.

Most recently, he began using Low Energy Precision Application (LEPA), which uses low-pressure nozzles and high irrigation efficiency in center pivot systems to minimize irrigated energy and water usage. LEPA systems are designed to match the amount of water application to the surface storage of the soil. LEPA nozzles are positioned close to the ground, usually no more than 18 inches above the crop, to minimize wind drift loss and evaporation.

Hansen produces irrigated and dryland crops. The dryland rotation is wheat, corn, confection sunflower, and fallow. His irrigated rotation is corn and confection sunflower, using 12 pivots from nine wells, two run on natural gas, the rest through electricity.

He ridge tills his silt-clay loam soil to use less water. Ridge till, explains the Kansas State University Extension Service, is a system in which seeds are planted into a seedbed that is prepared by scraping off the top of a ridge. The scraped-off ridge usually provides an excellent environment for planting. Ridges are formed during cultivation of the previous year's crop. Ridge till operations consist of planting in the spring and at least one cultivation to re-create the ridges for the next year. Rows remain in the same place each year, and any crop residue on the ridges at planting is pushed between the rows.

On poorly drained soil, seeds are planted in a warmer, better-drained seedbed than with most other tillage systems. Ridge till can greatly reduce erosion when compared to conventional tillage, especially when ridges are on the contour. Hansen leaves stalk residue to help catch snow over the winter, and doesn’t deep rip till, to conserve subsoil moisture.

Sunflower works well in the ridge till system, “but they do dry out the ground, so that’s why I water behind them,” says Hansen, and that’s why he follows dryland sunflower with fallow. A benefit with sunflower in his irrigated corn-sunflower rotation is that it has eliminated a $10-$18/acre insecticide cost to control rootworms in corn. The insect can be a problem in a continuous corn rotation, but doesn’t overwinter well when corn is followed by a different crop. “Rotation with sunflower helps,” Hansen says. On the other hand, the stem weevil is an insect that can be a problem in sunflower, which means rotating back to corn is beneficial too.

Unexplainably, in 1999 the irrigated sunflower he prewatered, then watered again at prebloom yielded several hundred pounds less than his dryland confection sunflower. He heard of other cases of this happening in 1999 too. Perhaps it rained during the prebloom irrigation, and the sunflower received too much moisture, or perhaps a disease came into play, he theorizes. At any rate, the phenomenon goes against conventional wisdom, which recommends watering sunflower before planting and again before bloom. “Maybe it was just one of those weird things that just happens sometimes,” he shrugs.

Hansen says his irrigated confection ‘flowers get the biggest boost from prewatering. He usually waters 2” per foot to fill the soil profile so it soaks to about 5 feet deep, monitoring with a soil probe to evaluate the water fill. Then he’ll focus on irrigating the corn, which he also prewaters before planting.

Most producers recognize that irrigated water is a limited resource, he says, and the switch away from flood irrigation is proof of that. There will be enough water for irrigation from the Ogallala for at least several more decades, and it’s possible technological advancements by then will make up for the reduction or loss of using Ogallala water. New irrigation technology already exists which automatically senses variable soil dryness across a field and waters accordingly, he points out. And years from now, genetically-engineered crops might be grown that are drought tolerant.

Hansen looks at the cost of irrigating—about $3/acre for flood irrigation in the 1970s, compared to about $50/acre now—and sees what might be an even bigger threat to the viability of irrigation than the water itself. “I think energy costs could get us before the depletion of water,” he says.—Tracy Sayler

High Plains producers facing limited irrigation try to water crops when they need moisture most.

Critical growth stages for major crops1.

Crop Critical period Symptoms of water stress Other considerations

Alfalfa Early spring and immediately after cuttings Darkening color, then wilting Adequate water is needed between cuttings

Corn Tasseling, silk stage until grain is fully formed Curling of leaves by mid-morning, darkening color Needs adequate water from germination to dent stage for maximum production

Sorghum Boot, bloom and dough stages Curling of leaves by mid-morning, darkening color Yields are reduced if water is short at bloom during seed development

Sugar beets Post-thinning Leaves wilting during heat of the day Excessive full irrigation lowers sugar content

Beans Bloom and fruit set Wilting Yields are reduced if water short at bloom or fruit set stages

Small grain Boot and bloom stages Dull green color, then firing of lower leaves Last irrigation at milk stage

Potatoes Tuber formation to harvest Wilting during heat of the day Water stress during critical period may cause cracking of tubers

Cool season grass Early spring, early fall Dull green color, then wilting Critical period for seed production is boot to head formation

Sunflower Preplant, bud and bloom Leaf wilting Most sensitive to moisture stress during flowering; least sensitive during vegetative period (emergence to early bud)

1 NRCS Colorado Irrigation Guide, NDSU, CSU

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