Looking for the Right Nutrient Formula for West Texas
April 9, 2024 Across the High Plains of Texas, the majority of cotton acres are irrigated through system heavy irrigation. Roughly 75% of the region’s irrigated acres utilize center pivot irrigation. However, the number of acres now irrigated through subsurface drip irrigation (SDI) has dramatically increased over the last 20 years.
“In 1998, we had approximately 20,000 acres of subsurface drip irrigation,” reports Dr. Katie Lewis, Associate Professor with Texas A&M AgriLife Research and Texas Tech University in Lubbock. “Today, it’s estimated that we have over more than 650,000 acres. With that increase comes questions about how to fertilize through the subsurface systems.
“With SDI, we can do more with the water we have,” she says. “Cotton may be less stressed because we’re able to provide it with water on a more frequent basis. We know that if we apply fertilizer through the drip tape right into the root zone, it can be used more efficiently. But we want to do the most with the nutrients that we’re applying.”
How can that be accomplished most effectively and efficiently? That’s the question driving Lewis’ research to develop nitrogen and phosphorus strategies to help optimize cotton yield as well as the fertilizer return on investment.
“More specifically, I want to determine the frequency of application,” she says. “How many applications of nitrogen and phosphorus do we need to apply? Do we need to use a spoon-feeding technique, or does it need to be simply one or three applications of these nutrients throughout the growing season?”
A spoon-feeding approach applies very small doses of nutrients throughout the growing season, and there are some company recommendations that suggest nutrient applications every 10 days. Lewis notes that this may be a better approach for nitrogen because it will allow growers to make more timely applications. But it’s possible to carry nitrogen too late into the growing season, leading to potential issues from excessive plant growth.
With phosphorus, because of the way it moves in the soil via diffusion, spoon-feeding could potentially cause some issues. Applications of small doses mean less movement and less uptake of phosphorus using spoon-feeding.
Lewis’ research was conducted in the Lubbock area over the past few years. Treatments were replicated four times, with nitrogen applied equally at 150 pounds per acre and phosphorus at 45 pounds per acre for all treatments. The study compared results from one application at the beginning of the growing season, three applications every 20 days, and nine applications every 10 days.
Soil samples were collected at multiple depths (0-6 inches, 6-12 inches, 12-24 inches, 24-36 inches) prior to planting and fertilizer application to determine existing elemental concentrations. Plant growth and health were evaluated throughout the season. Plants were collected at first open boll and separated into plant parts, dried, and weighed to evaluate nutrient partitioning within the plant.
Lint yield and fiber quality were also evaluated.
Based on results, the study suggested that different management approaches are likely needed for nitrogen and phosphorus when fertigating with SDI. More frequent applications of nitrogen resulted in greater uptake and higher yield response. However, with phosphorus, greater yield response was seen with fewer applications. More frequent applications increased phosphorus uptake but demonstrated possible antagonism with zinc that could limit yield potential.
“Based on the data we do have, I feel that very different management strategies are needed for nitrogen and phosphorus,” says Lewis. “I think growers can be more efficient with spoon feeding nitrogen as long as it’s not carried too late into the growing season.”
GET THE NEWSLETTER TODAY!
