By Brad Robb
After West Texas cotton growers were teased with several years of early-season rains, many made nutrient applications to capitalize on what looked to be a great start to each growing season. Some nutrients are likely still available for 2025. If Texas cotton growers were ever presented with an opportunity to save on up-front input costs at the start of a growing season, now might be the time.
“As our cotton growers prepare for planting, this is the best time to see a return on investment from soil sampling,” says Katie Lewis, Associate Professor, Soil and Fertility, Texas A&M AgriLife Research in Lubbock. “Because we had timely rains offering promising starts to the last several growing seasons, growers most likely applied fertilizer and other nutrients, fully anticipating having better than normal crops because of those early conditions. Then the rains stopped and the drought started, which is why farmers need to know the residual levels of those inputs.”
If fertilizer was applied before the drought and it never met the yield it was applied for, there will most likely be greater amounts of fertilizer in the soil than what may be anticipated. Because nitrogen and sulfur are extremely mobile in the soil due to their solubility, it’s possible these nutrients will be found deeper than six inches in the soil profile. Deeper sampling is necessary to better estimate what mobile nutrients might be accessible to the plant.
“That’s why it’s so important to take soil samples to find out exactly what’s left in the soil, and then credit that amount of fertilizer you need to apply,” Lewis explains. “I would even advise taking soil samples as deep as two feet to account for mobile nutrients that have been leached. Results from a sample that deep will give growers greater potential to save money upfront on next season’s nutrient requirements.”
Katie Lewis
Texas A&M AgriLife Research
Some fertilizer prices have eased, while others remained constant. Those variations create a financial consideration that supports her recommendation to take deeper core soil samples.
Across the Texas High Plains, it’s almost a 50/50 split of UAN 32 (32% nitrogen liquid) and urea (46% nitrogen dry prill) when it comes to a fertilization program. With approximately 40% of the High Plains cotton ground being irrigated and the rest under dryland production, 90-95% of those irrigated acres are under pivots.
When West Texas winds sweep across the High Plains and growers are making in-season fertilizer applications through pivots, the combination of high winds, alkaline soils and greater evaporative losses make the perfect environment for ammonia volatilization — a risk growers must consider.
Lewis always reminds growers about the “4Rs” of nutrient management that will reduce ammonia volatilization losses: right rate, right source, right time, and right placement. As long as fertilizer is incorporated more than 0.5 inches below the soil surface, volatilization losses will be dramatically reduced.
“While many cotton growers are putting most of their nitrogen fertilizer out through pivots, side dressing nitrogen remains an efficient method of application,” Lewis says. “We’re seeing more growers installing sub-surface drip systems every year, and they are fertilizing through the buried drip tape — an extremely efficient way to place the input right next to the root zone. This will result in greater plant uptake and less potential for losses.”
Dealing With the Drought
Despite early season rains in 2023 and 2024, conditions dried out again in mid-summer across the High Plains. At that point, Lewis knew that applying fertilizer late would do more harm than good, even for growers who were fortunate enough to get rain.
“With cotton being an indeterminate plant, I try to steer growers away from late August to early September applications of nitrogen,” Lewis says. “The likelihood of cotton putting more energy into vegetative growth rather than reproductive is always a possibility that late in the season, and excessive vegetative growth is the last thing you want when it comes time to defoliate and harvest. Hopefully, they had enough fertilizer out early on or there was sufficient residual nitrogen from the previous year to meet the demand of the crop.”
From a cost perspective, Lewis believes it is always better to apply what is needed for a specific (realistic) yield goal. With current fertilizer prices, apply a portion of what is needed up front and apply the remainder in-season. Research conducted across the High Plains demonstrated that a larger percentage of the nitrogen recommendation should be applied preplant, or closer to emergence when following a winter cover crop. This will increase nitrogen uptake and yield potential. It is always best to apply less mobile nutrients like phosphorus and potassium in closer proximity to the time of planting, and also closer to the root zone, to increase uptake by the crop.
Nitrogen Stabilizers – Conclusions from a Multi-Year Multi-State Study
Lewis and cotton researchers from Virginia, Tennessee, and Georgia collaborated in a multi-year research study evaluating fertilizer loss and the impact and value of nitrogen stabilizers. Initial results from the study confirmed up to 60% of a urea or ammonium-based fertilizer application can be lost through volatilization or leaching from the soil within a 72-hour period after it is applied.
“If a surface-applied application is made and not incorporated, or if some type of stabilizer product isn’t used to help keep that fertilizer in plant-available form, it could be a costly loss,” Lewis says. “Two options growers may consider are nitrification inhibitors and/or urease inhibitors, depending on the fertilizer source.”
Nitrification inhibitors help keep ammonium fertilizers from being transformed into a nitrate and leached through the soil profile or lost as a gas through a process called denitrification. Urease inhibitors temporarily limit the activity of the urease enzyme which converts urea into plant-available ammonium, thereby preventing loss through ammonia volatilization.
“The operative word there is ‘temporarily’,” Lewis says. “These products will help keep fertilizer in a form that will be less likely to be lost. It’s a microbially driven transformation and can last from up to 15 to 60 days depending on environmental conditions like temperature and field moisture levels.”
In West Texas, cotton planters begin rolling in May. Nitrogen uptake in cotton begins increasing 35 to 45 days after emergence and peaks around first bloom.
“Putting out a nitrogen application after first bloom or peak bloom is likely not going to be beneficial,” Lewis says. “Earlier is always better!”
Brad Robb is an agricultural writer based in Collierville, TN.
