A look under the soil at subsurface drip irrigation –

ITS CURRENT USE AND FUTURE POTENTIAL AS GLOBAL WATER AVAILABILITY STRETCHES TO ITS LIMITS.

Written by Treena Hein
This article was first published in New AG International in September 2021, and is reproduced here with permission of the author.

Farmers have always battled the elements, and they’re increasingly turning their eyes towards irrigation. Subsurface drip irrigation (SDI, or subsurface drip fertigation, SDF) is of particular interest due to the very low volumes of water involved, and the way SDF can deliver the right nutrients at the right time directly to plant roots.

SDI piping is laid down 10 to 20 inches beneath the surface of a field, orchard or vineyard. The emitters release water, with various nutrients added at specific levels and times depending on crop, plant growth stage, existing soil nutrient levels and so on.

Because SDF can result in impressive yields and its costs have come down, it continues to gain traction, particularly in high-quality crops and in semi-arid climates where evaporation greatly reduces the efficiency of overhead irrigation.

“Climate change and the threat of drought are definitely driving interest,” says Dr. Willemijn Appels, the Mueller Applied Research Chair in Irrigation Science at Lethbridge College in Alberta, Canada, where she has led a team of SDI and SDF researchers since 2018.

Appels and her colleagues have collaborated with Canadian firm Southern Irrigation, which has pioneered SDI use in Canada and has worked with Netafim (U.S.) for 35 years. Netafim (Israel) introduced the concept of SDI to the world, explains Southern Irrigation SDI sales rep Kees Van Beek.

“We have used their driplines for nurseries, market gardens, vineyards and greenhouses,” he says. “We installed the first 40 acres of SDI eight years ago in Gem, Alberta.” Across Canada, there are about 1,500 acres under SDI, mainly in Alberta, with a little in British Columbia and Saskatchewan. Southern Irrigation installed its biggest SDI field, 620 acres, in 2020.

Worldwide, Van Beek reports that millions of acres are irrigated with SDI on a wide range of grain, forage and fibre crops including alfalfa, canola, corn, cotton, soybeans and sugarcane. He says India and the U.S. are large markets for SDI, with extensive use of SDF in U.S. states such as Iowa and Idaho for corn and soybeans. All Mideastern countries use SDI, he notes, and most new irrigation acres in Africa are also SDI.

In Van Beek’s view, the potential for further adoption is very large. Along with all its benefits, SDI avoids the limiting factors of overhead (pivot) irrigation. Wind, for example, causes huge evaporation losses with overhead systems. The regular water spray can also be a significant cause of foliar diseases and crop lodging. Compared to SDI, overhead systems also have more moving parts, which means more maintenance.

But in Van Beek’s view, “the main driver for SDI will be the water savings. We use 30 percent less water and we are 98 percent efficient.”

Low Flow

Emitters have become smaller over time so they can accommodate very low flow rates. “The smallest ones I’ve used emit 0.11 gallons per hour,” notes Appels.

Van Beek says Netafim is the only manufacturer that makes these. He explains that with the use of these emitters, “we can run longer driplines while not increasing the dripline diameter. This helps with keeping the cost down. This low flow emitter matches the soil infiltration rate better, and we can run longer irrigation cycles.”

Van Beek says he believes that in the future, we will even see lower flow rates. Emitters will keep evolving, he notes, “and so will be the products we can inject to control the various aspects of crop health.”

Appels also notes that emitter designs have been improved such that roots and soil particles cannot plug the lines. The emitter holes are not big to start with and they only open when there is water pressure. More sophisticated pumping and filtration systems have also emerged, she says, along with continued improvement to automatization and remote control.

Field Crop Use

Already, reports Van Beek, “we know how and when to fertigate on crops like corn, soybeans [and] alfalfa from U.S. data, and we are learning to boost yields on canola, various kinds of wheat and other crops not grown on SDI in the U.S. With SDF, we have seen yield increases of up to 58 percent compared to pivot irrigation.”

According to Appels, there is increased interest from large-scale agriculture in Canada to use SDF with high-value crops such as canola and wheat (durum and winter wheat), but also hemp, timothy, alfalfa, silage corn and pinto beans.

“It may seem crazy at first to install it in an 800-metre by 800-metre block where every metre has a dripline – that’s kilometres of dripline – and grow canola on it, but the net returns can be worthwhile,” she says. “With a pivot on a square field you are going to miss some corners, but with SDI, you cover all the land. And using less water than with a pivot you can still get a good crop. It’s easy to automate, but you need the research to know when to apply water and fertilizer, how much fertilizer and so on.”

Study Results

There are multiple SDF projects going on at Lethbridge College, some in collaboration with industry partners. Here are details on some of them.

Over the last three years, Appels’ colleague Dr. Rezvan Karimi Dehkordi has studied how SDF can be used to maximize yields in field crops. Working with Southern Irrigation and First Fruit Farms near Lomond, Alberta, she has tested different SDF applications on durum wheat in 2019 and pinto beans in 2020. The 2019 study found durum wheat crops treated with subsurface fertilizers had higher levels of nitrogen and phosphorus uptake as well as higher yields. However, the 2020 study was affected by wet weather, and no significant differences emerged between study and control crops.

“When we have a lot of rain, the management of fertilization is complex with SDF,” says Karimi. “Early in a wet growing season, you would apply fertilizer on top of the soil and when it dries out, you can use fertigation, perhaps using higher concentration of fertilizer.”

In 2021, Karimi did greenhouse experiments examining the effect of fertigation frequency on nitrogen use efficiency and microbial communities in canola (which has a taproot) and barley (fibrous root). Analysis of data is going on right now. In 2022, at the new Lethbridge College demonstration farm, Karimi and her colleagues will compare fertilizer applications using different ratios of solid fertilizer applied to the surface, to fertigation via SDI over time, and at what concentrations to best boost yield.

“We look at the elevations, soil structure, soil horizons, water source and quality, crop rotation and rodent pressures to ensure success and a long-term relationship with our customers with agronomy support.”

Water Availability

For any type of irrigation anywhere in the world, farmers must be part of an irrigation district, with all parties removing water (such as municipalities and other industries) requiring a license for specific volume withdrawals over time. Van Beek says that in Alberta, there are over one million acres irrigated through 13 districts. Wells, runoff and dugout water storage are used as sources for irrigation in central Alberta and increasingly in Saskatchewan, Manitoba and further east in Canada.

“In southern Alberta,” says Appels, “we irrigate with surface water from a reservoir or river, transported by canals and pipelines to all in the network. The volume of water available is very dependent on snowmelt. In the U.S. Midwest, they’ve had water volume problems because their licences were for too much water and in many cases, they use aquifers which recharge slowly.”

However, she notes that water availability problems happen with surface water sources too. “In Alberta this year due to lack of rain,” she says, “the Milk River level dropped and farmers had to stop withdrawing for irrigation.”

Aquifer use in Alberta wouldn’t likely be an option, adds Appels, as most of the groundwater is found too deep below the surface and the water may be salty.

Cost Comparison

At this point, the cost to install SDI is higher than pivot irrigation. Each potential SDI adopter must of course investigate their options closely with a focus on potential benefits and ROI. This analysis, says Van Beek, includes all input costs, past yields, crop rotation, soil classification and more. 

“We take a very detailed approach to new SDI projects,” he says. “We look at the elevations, soil structure, soil horizons, water source and quality, crop rotation and rodent pressures to ensure success and a long-term relationship with our customers with agronomy support.”

2021-10-08T11:22:17-07:00September 24th, 2021|Press Release, Subsurface Drip Irrigation|