Irrigation Update: Hedging Against the Next Drought

hedging against the next drought micro irrigation web

The six-year drought that afflicted much of the western United States was one of the worst in California’s history, including a four-year span, 2011 to 2014, that was the driest since the state’s recordkeeping began in 1895. According to a study led by researchers from the University of California-Los Angeles, Central Valley farmers, lacking traditional access to flows from the melting Sierra snowpack, drilled more wells and extracted an astonishing 25 cubic miles of groundwater from the aquifers beneath the valley. 2,400 of those wells were pumped dry during the drought.

California farmers’ fortunes changed abruptly last winter: By May 2017, the state’s rainy season had set a record, establishing the wettest year on record, and many Central Valley growers raised record-breaking crops. On April 7, Gov. Jerry Brown declared the drought to be over.

The months since have been every bit as unsettled in California: The state has suffered the most destructive wildfires in its history and, last year, received very little rainfall in what is traditionally one of its two wettest months. And in four Central Valley counties containing most of the wells that dried up during the drought, farmers were buying water for delivery to above-ground tanks. According to NASA and Stanford University scientists, many of those underground water sources will never recover.

The climatic fluctuations underscoring the need for long-term stewardship of agricultural water resources are perhaps most pronounced in California, but they are by no means confined to the Central Valley. In August and September 2017, farmers on the high plains of Montana and the Dakotas were suffering from a so-called “flash drought” – a relatively new term denoting a period of sustained high temperatures and little rain – that ravaged the region’s wheat crops. The National Weather Service declared it the driest period in the region’s history. Farther south, in the High Plains region of western Kansas and eastern Colorado, some rain had fallen, bringing the area back into the average range of annual precipitation, but much of the area remained in moderate to severe drought. The Ogallala Aquifer, one of the world’s largest underground bodies of water, continues to be depleted at a rate significantly faster than it’s being replenished – and that rate is accelerating.

It’s grim news, but not yet apocalyptic. Farmers and their supporters in the scientific and research communities, aware that dramatic changes in water use will be required to weather the future uncertainty of precipitation, are experimenting with solutions involving the two primary factors in agricultural water consumption: soil and irrigation.

 

Soil

The intensity of industrial agriculture often compounds the risks of drought. It degrades organic matter that can help retain moisture, accelerates evaporative losses, encourages runoff, and reduces soil infiltration rates. All of these factors increase the amount of water needed to produce a crop.

preparing for drought no till web

Conservation tillage practices like no-till allow farmers to plant cash crop seeds with little disturbance to the soil, which protects the habitat for billions of the soil’s microorganisms. USDA NRCS photo

A growing body of research suggests that heavy plowing or tilling of agricultural soil actually decreases its ability to hold water and nutrients, and increasingly farmers are responding with conservation tillage (leaving crop residue in the field after harvest) to encourage infiltration and reduce evaporation, or, increasingly, no-till farming.

In spring 2017, South Dakota State University researchers evaluated different tillage methods on five fields. Among the results: The average time it took for an inch of water to soak into the soil in a cornfield that had not been tilled at all, and aerial-seeded with a cover crop of cereal rye the previous fall, was 27 seconds. In a cornfield that had been harvested and deep-ripped the previous fall, and then field cultivated and planted the day before the test, the average time for absorption was 9 minutes and 45 seconds.

Given the inconstancy of precipitation, farmers are also looking specifically at ways to prepare fields for unusual rainfall events. Stovers and wattles can maximize the amount of water that remains in the field by slowing runoff velocity, absorbing the energy of rainfall, and reducing the amount of soil particles swept away by flowing water, thereby allowing more time for infiltration. Plant residues also reduce evaporative losses by protecting from wind and high temperatures.

In the Mediterranean climate of western Marin County, California, which receives virtually no precipitation during the growing season, David Little has developed a dry-farming technique that allows him to lock in enough moisture to raise potatoes on the 30 acres of land he calls Little Organic Farm: Beginning as early as possible in the spring, when the ground is still wet from winter rains, he disks and plows his fields, and then smooths the surface with a light roller, leaving a crust that seals in moisture. Little compares it to a sponge wrapped in cellophane. “The water wants to percolate up,” he said, “even though that might seem counterintuitive. It rises up into the root zone and stays there. … I’ve tilled in March and then scraped the crust with my foot in August, and there is still some moisture under there.”

 

Irrigation

Dry farming is a suitable approach for certain soils and crops, but it tends to produce smaller fruits and vegetables and lower overall yields, which can work for a farmer earning a premium for organic produce, but can be difficult to scale up for large producers. It wouldn’t work, for example, for an almond grower in the Central Valley, where the traditional method of flood irrigation echoes how things used to be: In its former life, the valley was a long chain of wetlands, swamps, and sloughs that collected Sierra snowmelt and held it long enough to recharge massive underground aquifers. In areas with this hydrogeology, flood irrigation can be good for both farms and aquifers.

But this is increasingly not the case, obviously, as groundwater supplies continue to decline in the Central Valley. Flood irrigation is sometimes used for coastal row crops in places such as the Salinas Valley, where it’s not appropriate, and it’s being used at an expanding scale, during the hottest summer months, leading to unsustainable losses.

Flood irrigation is, by definition, imprecise, and researchers at the University of California-Davis and other institutions are working with almond growers on ways to optimize it. These partnerships are currently developing a distribution uniformity test, which will check to make sure an irrigation system is performing properly, and a continuous leaf-monitoring system that measures plant stressors to help estimate each plant’s water status. A growing number of almond producers and Salinas Valley vegetable growers are switching to micro-emitters rather than flood irrigation. A 2009 study by the Pacific Institute, a global water think tank, suggests that using such technologies, along with the soil moisture monitors now widely available, could allow farmers to calibrate water requirements and cut back on irrigation during drought-tolerant growth stages – saving as much as 6 million acre-feet (about 1.78 cubic miles) during a dry year.

preparing for drought soil health web

The Aggregate Stability Comparison display at a USDA Natural Resources Conservation Service soil health demonstration event uses two clear pipes with water to demonstrate the structural stability of healthy soil that has organic matter from cover crops and aeration created by worms and roots versus soil that is mechanically tilled on a regular basis and falls apart in water. Throughout the event, the no-till soil with organic matter maintained its structural integrity, while the high-till soil continued to fall apart in the water. Crops planted in soil that is better able to retain moisture require less irrigation. USDA photo by Lance Cheung

On the semiarid High Plains of Finney County, Kansas, where farmers tap the Ogallala Aquifer, several farmers are likewise working with the Kansas Water Office to operate demonstration farms combining wireless soil moisture monitors, well telemetry, flow meters, and several types of high-efficiency irrigation technologies – drip emitters, bubblers, and low-hanging circular sprinklers – that can be adapted to fit existing center-pivot irrigators and apply water closer to the ground, allowing greater penetration and less evaporation. One of the so-called Water Technology Farms, T&O Farms, is owned by Tom Willis, who grows wheat, sorghum, soybeans, and forage crops such as alfalfa and triticale. By avoiding evaporative losses and slowing the rate at which he pumps from the aquifer, Willis, in his second season, has been able to cut his water use by 40 percent. “What I’m seeing is that where I was able to slow my wells up,” said Willis, “the static water level on the first of August was 10 feet to 12 feet higher than it was the year before.”

Dwane Roth’s Big D Farm in Finney County receives water from two sources: underground, from the Ogallala, and surface water from the Arkansas River. He decided to operate one of the experimental farms at the urging of his friend – essentially, his landlord. He’d known of the programs and assistance available from the state over the years, but he’d mostly kept to himself, even refusing the offer of wireless soil moisture probes from the water office. “I was too damn smart,” he said. “This program has really opened my eyes. You know when you get into a lull, where everything’s good enough, just because it’s the same it’s always been? But the most precious resource we were using – I wasn’t doing my best with it.”

Roth is in his second season of growing corn in three row circles, each using a different applicator attached to the pivot span. The scheme of tracking moisture with probes and adjusting well output to match water needs, he said, “has really opened my eyes. … Out of the aquifer this year, on one circle, I used 5 and one-half inches. My cousins, right across the road, used 10 more inches than I did. They didn’t have the probes. I grew 241 bushels of corn, and they grew 233.” Like Willis, Roth has seen the static water levels in his wells rise over the last year, though he cautions that in a drier season, it will be far more difficult to avoid depleting the aquifer further.

Still, the Water Technology program’s first two years are encouraging. CropMetrics, the company supplying Roth’s moisture probes and helping him to make data-based decisions, has calculated that the technologies and water management support used on Roth’s acres resulted in the application of about 25.9 million fewer gallons per field, for a savings of about $4,266 in irrigation costs per field and, all told, an average increase of more than $45 in profit per acre.

Those numbers should be enough to convince anyone to become a more careful steward of water, but recent studies of the Ogallala Aquifer might lend a sense of greater urgency: Kansas State University researchers recently reported that at the current rates of extraction, 70 percent of the Ogallala will be gone by 2060 – and once depleted, depending on the location, it will take 500 to 1,300 years to refill naturally.

“We didn’t know how bad we were overwatering before,” Roth said. “In western Kansas, you can’t bet on the rain. I think this program has us on the verge of really changing the way we do things.”

Caption for top photo: spray water from a low height for several feet to keep water on the trees’ root zones, and water is sprayed at a predetermined rate to customize the efficient irrigation of each tree. USDA photo by Lance Cheung

This article was originally published in the 2018 edition of U.S. Agriculture Outlook.

Leave a Comment

  • (will not be published)