Rooted in resilience

The approach to the intersection of soil health and irrigation is a significant step toward the goal of sustainable agriculture and the balance of crop productivity with environmental stewardship.

Cameron Ogilvie, a Soil Health Institute soil health educator, notes four points as to why healthy soil is essential for effective water management.

“First, healthy soils are better able to absorb water,” he points out. “When soils have been degraded, they lose their ability to absorb water. The pores and channels that allow water to infiltrate get plugged with soil as weak soil aggregates fall apart, or ‘slake,’ from rain or irrigation water.

“You end up with water running off the field or ponding on the soil surface. Healthy soils have strong aggregates that stay intact when they get wet, and there are open pores that allow the water to soak in and get to where the crops can use it.”

Second, healthy soils can hold more water in reserve for crops to use later. “Healthy soils have higher levels of soil organic matter and better soil structure and porosity — like a sponge,” Ogilvie says. “Once water has been absorbed into the soil, the higher organic matter and better structure means there’s more storage space for water to be held onto rather than draining out of the root zone.”

Degraded soils have lost soil organic matter and porosity, resulting in less storage capacity in the soil for water, he adds. “Through our research, we’ve demonstrated that a 1% increase in soil organic carbon — the carbon fraction of organic matter — can increase the water holding capacity of soil by as much as 5,300 gallons per acre in the top 6 inches,” Ogilvie says.

Third, healthy soils make it easier for crops to access water. “One sign of soil degradation is soil compaction, which restricts root growth,” Ogilvie says. “Healthy soils are less prone to compaction, and roots can grow more freely and access water stored in the soil.”

Finally, soils armored with crop residues lose less water to evaporation. “Crop residues act as a mulch, shielding the soil from the sun and reducing the loss of soil moisture,” Ogilvie says. “When we expose soil to the sun, the dark soil quickly heats up and we lose water that could have been used by crops.”

“Healthy soils are well-balanced soils rich in biological activity; have excellent soil structure such as porosity, bulk density and aggregate stability; and are rich in the elements required for building life — carbon and other macro and micronutrients,” notes Jackson Stansell, Sentinel Fertigation founder and CEO.

Irrigation can impact the physical, chemical and biological properties of healthy soil, he adds. “Irrigation with inappropriate water flow dynamics can disturb soil surface structure, leading to erosion and degradation,” says Stansell. “Overirrigation can saturate pore spaces, deoxygenating the soil and forcing microbial populations into anaerobic conditions that are select for certain organisms as well as alter nutrient availability dynamics.”

Underirrigation can impede biological activity and limit nutrient availability and crop uptake dynamics, Stansell notes. “Ultimately, healthy soils provide resilience against extreme conditions, even when it comes to water. Irrigators should seek to manage irrigation to maintain optimal soil moisture conditions to empower their soil to sustain resilience in these extreme conditions,” he says.

Water quality and management

Irrigation is important to soil quality because irrigation systems move more than just water into the cropping system, notes Glen Ritchie, PhD, professor of crop physiology and chair of the Texas Tech University Department of Plant and Soil Science. “Irrigation water quality is of utmost importance. Water with high levels of sodium and other salts can create long-term salt issues,” he says. “Furthermore, irrigation application can move salts away from the plant growing environment if done correctly, and proper irrigation prevents soil erosion, leaching of nutrients and other negative effects to the soil.”

Addressing how effective water management supports sustainable agriculture, “When I think of sustainability, the first word that comes to mind is resilience — the ability to continue to produce great crops even under difficult circumstances,” notes Ogilvie. “We’re seeing more extreme weather events these days: longer droughts and heavier rains. Improving soil health is the first step to building resilience into our farms so we can weather the weather.”

That largely comes down to “being able to manage water effectively and making the most of the water we do get: getting water to infiltrate into the soil, holding onto as much of that water as we can, minimizing how much of it gets lost and making sure that our crops have easy access to that water when it otherwise is limiting,” Ogilvie says.

In arid and semi-arid regions, irrigation is an important limiting component of agricultural production, Ritchie notes. “Water management impacts both current productivity and future crop production capability,” he says. “For example, in the Texas High Plains, water is drawn from the Ogallala Aquifer, which does not recharge in a timely manner in the region. As a result, every gallon of water withdrawal is considered a removal of a future resource, and management must be balanced for long-term productivity.”

In regions with fewer restrictions on water availability, the competing demands of agriculture with municipal and other needs make efficient use critical as well, Ritchie says, adding “effective water management in more humid regions includes minimizing runoff or leaching of water, which often has agricultural products in it.”

Stansell notes it’s important to define sustainable agriculture holistically, involving not only environmental stewardship but also the ability for a farm to produce fuel, food and fiber for a profit indefinitely.

“Understanding water management in the context of sustainable agriculture requires first understanding water quantity and water quality,” he points out. “Managing water quantity for sustainable agriculture means seeking to manage irrigation events in such a way that optimal productivity is reached without applying more water than can be recharged in the source water system over an acceptable recharge period.”

If only 30 inches of water can recharge over a three-year period, no more than 30 inches of irrigation should be used to grow crops during that period, Stansell adds. “Maybe this means exceptional management, as many growers are already achieving, and maybe this means selecting crops that are better adapted to low moisture conditions,” he says. “Water quality also plays a role. Understanding whether your water will increase soil salinity without the appropriate volume of water applied in each irrigation event is critical to maintaining the long-term productivity of the soil.

“Similarly, not overirrigating will help to preserve soil structure and nutrient content in the soil without driving water-soluble nutrients into water resources, potentially unlocking contaminants or resulting in eutrophication, among other impacts.”

Innovations

In terms of the latest innovations in soil moisture monitoring, Stansell notes some of the most interesting technology he has seen for soil moisture monitoring is leveraging remote-sensing data — including synthetic aperture radar and thermal data — to spatially map changes in soil moisture at landscape scale and sub-field resolution.

“What this allows is low labor soil moisture tracking for decision-making and even spatially variable irrigation management,” he says, pointing to Nave Analytics and Aperture Space as examples.

Several high-quality moisture monitoring systems are available commercially, and there are several accurate soil moisture sensors — many of which have been available for more than 20 years, Ritchie says. “Perhaps the most exciting innovations are the integration of these measurements with remote sensing, weather information, crop modeling and geographic data to allow decision-making that interpolates sensor data across fields, management systems and larger areas,” he notes.

Addressing the latest innovations in irrigation scheduling, Stansell notes remote soil moisture monitoring also is being integrated with in-field sensors and models to produce comprehensive insights on soil water availability and crop water uptake that can inform highly accurate forecasts of crop water demand, allowing producers to schedule irrigation events with more time for planning, citing Goanna Ag.

Ritchie notes most irrigation scheduling innovations with which he is familiar integrate soil moisture sensing and modeling with evapotranspiration measurements and in-season imagery to advise irrigation scheduling. “Wireless communication and uploads to the cloud have become standard for many of these sensor systems,” he says.

Addressing the latest technologies designed to balance crop productivity with environmental stewardship, Stansell says that outside of water quantity management, another major contributor to environmental stewardship is nutrient management.

“Several technologies have entered the market in the last 15 years providing nutrient management guidance, particularly for nitrogen management,” he says. “Many of these technologies have focused either exclusively on remote sensing to react and respond to nitrogen deficiency symptoms in crops or on modeling to estimate soil nitrogen availability and crop nitrogen uptake to inform application rates prior to or throughout the growing season.”

Each of those techniques has flaws, Stansell notes. “Remote sensing alone lacks the predictivity to inform the appropriate rate for a final nitrogen application during the season,” he adds. “It can be augmented with historical production and other data to improve recommendation outcomes. Models alone are often over-generalized, and due to their reliance on coarse weather data, can provide highly erroneous results.

“New technologies … fuse these two techniques to deliver a complete solution for comprehensive nitrogen management that is built to optimize for profit, efficiency and productivity, ultimately increasing or maintaining yields while limiting the risk of water contamination with nitrates.”

Most irrigation technologies are designed around reduced water application and maximizing production within a given level of irrigation, says Ritchie. “Work has been done to improve yields through both irrigation rate and timing to improve water use efficiency,” he adds.

Carol Brzozowski is a freelance writer with a specialty in environmental journalism based in Venice, Florida. She can be reached at brzozowski.carol@gmail.com.