Employing deficit irrigation is one way for farmers to protect crops against dry conditions and achieve respectable yields, while not breaking the bank. 

Deficit irrigation is a supplemental irrigation strategy that focuses on applying less water than a crop’s full water requirements. 

North Carolina State University Extension water resiliency specialist Chad Poole is a believer in deficit irrigation when water supplies are inadequate, because it allows farmers to manage limited water and only irrigate when the crop is most sensitive to water deficit conditions. This can make a big difference in determining final yields. 

Water holding ponds 

One water source for deficit irrigation is water holding ponds that can channelize surface water into the pond to capture the water for irrigation during the dry periods of the growing season. Pond size and construction costs vary, thus limiting water quantities. 

Poole, colleagues Mohamed Youssef and Hossam Moursi, and graduate students at N.C. State have been conducting research on crop yield and water quality benefits of holding ponds for over six years now.  

Based on this research, NCSU researchers believe this system has a place in North Carolina. One of the research sites is at the Peanut Belt Research Station in Lewiston-Woodville, where a seven-acre pond provides an irrigation capacity of 725-acre inches of water. 

Poole said this is not a lot of water, considering the farm has irrigation capacity for approximately 250 acres of cropland. For each irrigated acre, it can supply less than three-acre inches of water without refilling, but he said the water can be targeted when corn or other thirsty crops need it most to maximize yields.  

He adds that the water quality in the holding pond is excellent. 

During the CHROME Ag Expo Aug. 21 at the Peanut Belt Station, Poole highlighted this research work on water holding ponds and emphasized the benefits of using deficit irrigation to improve corn yields. For corn, Poole said water is most needed from tasseling through milking to maximize yields. 

“Knowing when that ear is going to fill out and when it is pollinating makes all the difference in the world,” Poole said. 

Increasing nutrients and yields 

Poole said research from 2022-2023 shows that applying water when it was needed during these stages of growth boosted corn yields. 

In 2022, the research team saw a 116% increase in corn yield using deficit irrigation. The next year, they saw a 59% increase in yields. “The top end yields both years are pretty much identical,” Poole said. 

Importantly, Poole said irrigation allows the corn plant to take up more nitrogen and phosphorus than non-irrigated corn. “Not only can we increase revenue at the end of the season, but we can also make sure that fertilizer you’re putting out gets used to make that grain. Irrigation is allowing us to do that.” 

An added benefit of irrigation and the water holding ponds is that it helps minimize nutrient runoff downstream, a huge benefit to water quality. Poole said the pond at the Peanut Research Station averaged a 16% capture rate of runoff the previous two years even with pump repairs during the growing season.   

“That’s over 200-acre inches of additional water conservation on average without having to put in a well. That’s not a lot of water on a 300-acre farm, but at the right time it can make us a lot of money. More importantly, the fertilizer that we’re losing through the runoff is captured and treated by the pond. Nitrogen loss is reduced by over 40% and phosphorus loss is reduced by over 60%,” Poole said. 

Soil loss to offsite receiving surface waters is reduced by over 90% by having the pond at the station. 

Poole encourages farmers to participate in the Agricultural Water Resources Assistance Program, or AgWRAP, which is administered by the North Carolina Soil and Water Conservation Commission through local soil and water conservation districts. Poole said it is a cost share program that will pay up to 75% of the cost of a water capture pond.  

Poole pointed out that work at the Lewiston-Woodville station has been supported by a USDA Conservation Innovation Grant (CIG) and Cotton Incorporated.