Research for Better Water Management: Not Too Wet, Not Too Dry

Mother Nature can be fickle when it comes to providing the right amount of water at the right time for North Carolina crops, and climate change is expected to make water management even trickier for farmers.

At North Carolina State University, Professor Mohamed Youssef and a team of engineers and students from the College of Agriculture and Life Sciences are developing and testing new methods of water management to achieve complementary goals – to help farmers increase their yields and to prevent water quality problems downstream.

“This research is for tomorrow’s agriculture – climate resilient, environmentally sustainable and resource efficient,” said Youssef, of NC State’s Department of Biological and Agricultural Engineering (BAE). “It applies the technologies that are available today to adapt and improve agricultural systems for tomorrow’s challenges – actually, for today’s challenges, because the too-wet conditions and too-dry conditions during the growing season are now upon us year after year.”

Building on Past Research

Some of the technologies the researchers are testing build on NC State-developed controlled drainage strategies that have been used for decades to manage water levels. Controlled drainage cuts the loss of nitrogen and phosphorus applied to farm fields. Nitrogen and phosphorus are important fertilizer components, but they can cause pollution when they flow with drainage water into streams, estuaries and oceans.

Thanks to state and federal cost-share programs, over 4,500 controlled drainage structures have been installed on Eastern North Carolina farms in the 1980s and 1990s and many continue to be used today.

Proper management of controlled drainage provides a healthy environment for crop growth while reducing nutrient losses to surface waters.

The practice uses control structures installed at drain outlets to regulate drainage from fields based on farming needs. Managing the drainage control structure is done by stacking wooden boards to the structure to store water in the field or removing the boards from the structure to release water from the field, depending upon the need for drainage. “Proper management of controlled drainage provides a healthy environment for crop growth while reducing nutrient losses to surface waters,” Youssef said.

But controlled drainage has a major drawback. Farmers have to manually add or remove the boards to control moisture in the field, and that can be time-consuming and physically demanding if the boards have swollen.

Two technologies, both featured at the 2020 Virtual Blackland Farm Managers Tour, represent particularly promising next-generation water management options.

Under Youssef’s leadership, the systems are being tested at two farm sites in Beaufort County, where the Pamlico and Pungo Rivers drain into the Pamlico Sound.

A Catch-and-Release Approach

Researchers are evaluating drainage water recycling as a practice that contributes to achieving climate resilient, environmentally sustainable. The practice involves the capture and storage of agricultural runoff, from both surface and subsurface flow, during wet periods in on-farm reservoirs. The water is reused for supplemental irrigation during dry periods of the growing season. Results at a Belhaven farm have shown that the practice can reduce nitrogen and phosphorus losses to downstream surface waters by about 50% and sediment losses by about 90% while increasing crop yield by about 30%.

At a farm in Belhaven, researchers are considering whether draining excess water from a field to a storage pond and then later using the water as a supplemental irrigation source during dry periods can increase yields. They are also studying how well the system effectively captures and reuses nitrogen and phosphorus in ways that improve the quality of downstream water bodies.

On the 65-acre site, Ph.D. student Hossam Moursi has been studying the drainage water recycling system for three years. The new system uses controlled drainage and subirrigation. During wet periods, water flows to a one-acre storage pond. The pond collects water from three areas – the experiment site, a control field without irrigation, and a nearby forested area. During dry periods, the collected pondwater is pumped into a tank, then feeds a subsurface irrigation system.

So far, the researchers have found that the automated system assimilates and recycles about 80% of the nitrogen and nearly 50% of the phosphorus that comes from the field to the pond, Moursi said. In addition, it reduces sediment by 90%.

Crop yield results have also been positive. In 2018, soybean yields were up 30%. In 2019, a particularly dry year, the field was planted with corn, and while the overall yield compared to the long-term average wasn’t high, the researchers did see benefits over what they saw in the control field.

We are comparing how much crop yield that you can get compared to how much area of agriculture land that you can take off of the farm.

Youssef characterized the results so far as “exciting.” Ongoing studies will give the researchers a better idea of whether the improvements will hold up over time and with different crops.

Meanwhile, researchers are using computer modeling to determine site-specific pond sizes that account for soil types and long-term weather conditions.

“We are also considering the area that you are taking out of production to build the pond,” Youssef said. “It’s a tradeoff, so we are comparing how much crop yield that you can get compared to how much area of agriculture land that you can take off of the farm.”

The researchers also want to explore whether the ponds could be managed to mitigate floods – an important consideration, given climate change, Youssef said. Scientists have predicted that with a warmer climate, hurricanes could intensify, producing more rainfall and leaving more floods in their wake.

Around-the-Clock Monitoring and Management

About three miles from the Belhaven site, on a 115-acre farm field in Bath, NC State has implemented a one-of-a-kind real-time water management system. The system is designed to help farmers keep soil moisture at levels that are ideal for plant growth – not too wet and not to dry – throughout the growing season.

The goals are similar to those with the drainage water recycling project – to raise yields and to cut the loss of nutrients from the field.

Doctoral student Ehsan Begheri is examining the effectiveness of the solar-powered real-time water management system in several scenarios involving free drainage, controlled drainage, and subirrigation.

The system consists of monitoring stations where instruments measure water table depths as frequently as every 10 minutes. The monitoring stations send signals to control stations engineered with gates that raise and lower the water level in the field.

“When the water table in the field gets too close to the field surface, the bottom gate will open and let the water be exported from the field, and when the water table in the field is getting too deep, the control unit will take action and close the outlet and pump water back to the field,” Begheri explains.

Begheri, who has worked on the project for three years, says that the computerized system responds based on a range of factors – the depth of water table in the field, the depth of water at the outlet, rainfall amounts, crop type and the crop growth stage.

The goal is a system that more than pays for itself by saving on energy, water consumption costs and nutrient use.

“This technology gives us the ability to know what’s going on with the water table in real time and to manage those levels in the field,” added Chad Poole, a water resiliency specialist with NC State Extension. “Essentially we’re taking the headache away from the growers of having to do this.”

Poole also initiated a field experimental study at the same site to determine which crop varieties perform best when it’s wet and which ones are best when it’s dry.

“We have a drip irrigation study going on, where we’re evaluating moisture meters that growers can use to trigger irrigation,” Poole said. “We basically saturate some of the varieties in one treatment and then keep the moisture consistent in another, and then let the natural conditions occur for one of them, and compare yields across. That allows us to be able to give farmers an idea of which varieties will respond to different soil and moisture conditions and what kind of nutrient requirements would be necessary for that variety to achieve optimal yields.”

The goal in these studies, Poole added, is to come up with a system “that more than pays for itself by saving on energy, water consumption costs and nutrient use.”

“What this technology offers farmers is a way to have a cost-savings on water. Ultimately, we want to use every drop of water that we receive first before we have to pump out of the aquifers or some other water source,” Poole said.

Youssef said that the real-time water monitoring project will continue for three or four years if funding is available, and the results could shape agricultural water management for decades to come.

A Quest for Answers

Professor and BAE Department Extension Leader Michael Burchell said that the researchers and students involved with the agricultural water management research aim “to find the most economical solutions possible, with the best results both for the farmer and for the environment.

“They’re trying to help farmers avoid the pitfalls of trial and error, which gets expensive,” he added. “Let the researchers do the trial and error, and then they can give the most definitive information to help them get it right the first time.”