Freshwater Scarcity and Saline-Water Irrigation
Diminishing freshwater resources and related issues of saline intrusion and saline soils aren’t just regional issues reserved for desert climates. These global concerns mandate changes, not only in how agriculture uses water, but also in the water it uses and the crops it grows.
In response to these challenges, a research team comprised of members from Clemson University, University of Florida, and the USDA’s Agricultural Research Service is tackling the problem with a CEA twist: the development of a hydroponic platform to grow salt-tolerant crops with saline-water irrigation, without negative environmental impact.
Boosted by a $10 million USDA National Institute of Food and Agriculture grant, the project led by agricultural scientist and project director Dr. Raghupathy Karthikeyan, Clemson’s Newman Endowed Chair of Natural Resources Engineering, and co-project director and environmental engineer Dr. Gary Amy, Dean Distinguished Professor in the Clemson Department of Environmental Engineering and Earth Sciences, launched about one year ago.
CEA to the Rescue
Dr. Amy noted that people often think about climate change–induced drought in places like California, Texas, or the Middle East. However, low elevation makes places like South Carolina and Florida vulnerable to climate change-induced saltwater intrusion into aquifers, as well as river deltas and estuaries.
As sea levels rise and the so-called “salt line” moves inland, every aspect of crop production must adjust. Finding ways for traditional agriculture to use saline water to irrigate salt-tolerant crops simply creates more problems.
“You’re using marginal-quality saltwater and you’re putting it on the land and you’re salinizing the soils,” Dr. Karthikeyan explained. “The rough estimates are if you put one gallon or one liter of saltwater in the soil, it could take anywhere from 30 to 300 liters to flush it out depending on the site. That is why we are using this hydroponic system.”
With a hydroponic CEA platform, water is recycled, brine is controlled, saltwater is controlled, and growers know exactly where saltwater irrigation will be captured, reused and recycled. “That’s why we are advocates of hydroponics in this particular application,” Dr. Amy added.
A New Desalting Paradigm
The current desalination mindset focuses on drinking water, not agriculture, Dr. Amy explained.
“It’s looking at achieving very, very low levels of salt that are consumable by humans. We’re looking at an opposite perspective here,” he said. “We’re looking at salt-tolerant crops that can tolerate higher levels of salinity where maybe we have to do what we call partial desalting.”
While the energy footprint and unit costs of complete desalination for drinking water are high, Dr. Amy said, partially desalting is much less energy intensive.
“We’re thinking about a new paradigm for how we desalt for salt-tolerant crops,” he said.
The research goes deeper than overall salinity to explore nutrient optimization of saltwater sources; for example, by retaining beneficial ions such as calcium in the desalting process, while minimizing others.
CEA’s complete control is integral to the idea.
“The crop water use in CEA could be 1/10 to 1/100 of conventional systems,” Dr. Karthikeyan said. “So it’s not only that partial desalination is cutting energy, but obviously we’re not going to be treating humungous volumes of water. The water we are going to be using is also very small, very minimal.”
Hydroponic crops under study include mustard greens, cucumbers, and tomatoes.
Photos: Hydroponic image (combined by Dr. Karthikeyan): Mustard greens. (c) Branham, Clemson University. Cucumbers. (c) Kousik, USDA-ARS. Tomatoes. (c) Ling, USDA-ARS
Target Crops, Tailoring Salinity
The research focuses on three crops — mustard greens, cucumbers, and tomatoes. Chosen not for existing salt tolerance, they represent high-value crop families from Brassicas and leafy greens to high water-usage crops to tomatoes, an obvious choice, Dr. Karthikeyan said, as it is the number one vegetable crop that is consumed.
Still early in the project, the team is now focused on pre-breeding and phenotyping well over 1,000 lines of the three vegetables for salt acclimation. The screening ranges from wild and landrace types to stable, commercially available varieties, accumulated from all over the world.
Ultimately, the program will develop new varieties with varied levels of saline tolerance for commercial production and further breeding. CEA growers will be able to choose varieties suited to saline levels in their irrigation water or tailor saline irrigation levels to match their crop.
“In terms of salt tolerance, this is not a cliff. It’s a continuum,” Dr. Amy said. “As you lower the salinity, you get a greater yield. But it costs money to lower the salinity, and then we have to think about the desalting investments we have to make in order to achieve that.”
In the end, the researchers aim to find that sweet spot of optimum crop yield and nominal desalting energy and costs. At the core will be hydroponic CEA facilities using naturally occurring saline water to grow food crops — without jeopardizing freshwater resources or salinizing soils.
This article is part of our inaugural edition of CEAg World Insights. Click here to view the entire interactive report.