Amaral: Building Yield from the Ground Up – Soil Fertility Considerations for Georgia Cotton

Douglas Amaral, Assistant Professor & Extension Soil Fertility Specialist
Department of Crop & Soil Sciences, University of Georgia

Cotton production in Georgia has always required careful management of multiple moving pieces such as variety selection, planting conditions, pest pressure, and weather. But one factor that quietly influences every one of those decisions is soil fertility. As the newest soil fertility and plant nutrition specialist with the University of Georgia Extension Cotton Team, my goal is to help growers optimize nutrient management strategies that support yield potential while protecting long-term soil productivity as cotton remains one of Georgia’s most important row crops and plays a critical role in the state’s agricultural economy.

My Background and Role at UGA
Prior to joining UGA, I spent 10 years with the University of California Cooperative Extension, where I worked on plant nutrition and soil fertility management in specialty cropping systems, including tree nuts and other high-value crops. That experience reinforced the importance of developing nutrient management strategies that are both scientifically sound and practical for growers. In December 2025, I joined the University of Georgia as an Extension Specialist in Soil Fertility and Plant Nutrition with the Department of Crop and Soil Sciences. My program focuses on improving nutrient management efficiency across major agronomic crops including cotton, peanut, corn, and soybean. My work combines applied field research with Extension outreach to help growers make practical, science-based fertility decisions. That includes evaluating nutrient management strategies, fertilizer sources, soil amendments, and emerging technologies that improve nutrient use efficiency. In Georgia’s Coastal Plain soils which are typically sandy and prone to nutrient leaching effective fertility management can be the difference between average yields and top-end performance.

Start with the Soil Test
One of the most important tools in cotton fertility management is still the soil test. Without it, fertilizer decisions become little more than educated guesses. The UGA soil testing program provides recommendations tailored to Georgia soils and production systems. Maintaining proper soil pH is often the first priority. For cotton, the target pH range is generally around 6.0-6.5, which supports nutrient availability and healthy root development. When pH drops below or above this range, nutrient availability can be affected. Lime applications are often one of the most cost-effective investments a grower can make.

Plant Nutrition: Finding the Balance
Nitrogen management in cotton is a balancing act. Too little nitrogen reduces yield potential and fiber quality. Too much nitrogen can create excessive vegetative growth, increase boll rot risk, delay maturity, and complicate defoliation. UGA recommendations generally base nitrogen rates on yield goals. For example:

These recommendations should always be adjusted based on soil type, previous crop, and field history. Cotton following legumes such as peanuts or soybeans may require less nitrogen, while deep sandy soils may require a different nutrient management approach. Split applications are often beneficial, with a portion applied at planting and the remainder at sidedress to ensure nitrogen availability during peak crop demand.

Potassium deficiencies remain one of the most common fertility issues in Georgia cotton production. Adequate potassium is critical for boll development, fiber quality, and overall plant health. Many Coastal Plain soils have limited potassium reserves and can quickly become depleted under high yield conditions. This is why potassium and pH are often considered two of the most important numbers on a soil test report for cotton production. Maintaining adequate potassium levels helps support water regulation within the plant, improves stress tolerance, and contributes to strong boll retention.

Sulfur has become an increasingly important nutrient in cotton production over the past two decades. Historically, sulfur deficiencies were rare because atmospheric deposition from industrial emissions supplied a significant portion of crop needs. However, cleaner air regulations have significantly reduced sulfur deposition, and deficiencies are now more common, especially in sandy soils. Sulfur plays a key role in protein synthesis, chlorophyll formation, and nitrogen utilization. When sulfur is deficient, cotton plants may appear pale green or yellow, particularly in the younger leaves since sulfur is relatively immobile in the plant. These symptoms can sometimes resemble nitrogen deficiency but typically occur on newer growth first. Georgia’s sandy Coastal Plain soils are particularly susceptible to sulfur deficiency due to low organic matter and limited sulfur-holding capacity. Sulfur can also leach from the root zone during periods of heavy rainfall. In many situations, applying 10-20 pounds of sulfur per acre is sufficient to prevent deficiency in cotton. Sulfur is often supplied through fertilizers such as ammonium sulfate, ammonium thiosulfate, blended fertilizers containing sulfate, and gypsum. Including sulfur in preplant or sidedress fertilizer programs can help ensure adequate availability during early vegetative growth when cotton demand begins to increase.

While nitrogen and potassium tend to receive most of the attention, micronutrients and secondary nutrients also play important roles in cotton production. Boron is particularly important for reproductive development and boll retention. In some cases, tissue testing during the growing season can help diagnose emerging deficiencies and guide corrective management decisions.

Potassium Nutrition and Cotton Jassid: An Emerging Challenge
One area of growing interest is the relationship between potassium nutrition and the two-spotted cotton leafhopper (Amrasca biguttula, known as cotton jassid) management. Cotton jassid is an invasive pest that has recently emerged as a concern in parts of the Southeast, and growers are actively learning how to manage its impact on yield and plant health. Cotton jassids feed by piercing plant tissues and removing sap from leaves. This feeding can cause leaf curling, yellowing, and reduced photosynthetic capacity, which ultimately affects plant growth and boll development. While insecticide tools remain important, there is increasing interest in understanding how plant nutrition influences plant tolerance to insect feeding.

Potassium plays a particularly important role in this interaction. Adequate potassium levels help regulate water balance, stomatal function, and carbohydrate movement within the plant, all of which contribute to plant resilience under stress conditions. Cotton plants that are deficient in potassium often show increased susceptibility to environmental stress and may recover more slowly from pest injury. In Georgia’s sandy Coastal Plain soils, potassium levels can decline quickly under high yield conditions, making regular soil testing and proper fertilization especially important. Ensuring adequate potassium nutrition may help maintain stronger plant growth and potentially improve the crop’s ability to tolerate stress caused by pests such as cotton jassid. Over the coming season, one goal of the soil fertility program in collaboration with the cotton team at UGA is to evaluate how potassium fertility programs interact with cotton jassid pressure, with the goal of providing growers with science-based recommendations that integrate nutrient management and pest resilience.

A Systems Approach to Cotton Fertility: The TRAP Principle
One of the biggest challenges in nutrient management is recognizing that no single nutrient works in isolation. Cotton yield is influenced by a combination of soil properties, nutrient balance, weather conditions, and management decisions. A successful fertility program should consider soil test levels, soil type and texture, crop rotation, yield history, irrigation and rainfall patterns, and nutrient interactions. By viewing fertility as part of a larger production system, growers can make more efficient fertilizer decisions and reduce unnecessary inputs.

For years, growers have relied on the 4R’s of nutrient stewardship (Right Source, Right Rate, Right Time, and Right Place) as the guiding principles to optimize fertilizer use. While the 4R’s framework provides a solid foundation, it is a bit abstract, and all the “Right” repetition doesn’t make it easy to remember what actually needs to happen hindering widespread adoption and practical implementation on many farms. To help guide nutrient stewardship decisions, my program focuses on what I call the TRAP principle, a simple framework that helps growers evaluate fertility decisions in a more integrated way. TRAP stands for:

Using a framework like TRAP encourages growers to think about fertility management as a complete system rather than a single fertilizer application decision.

Looking Ahead
My goal with the UGA Extension Cotton Team is to support growers with practical research and timely recommendations that improve profitability and sustainability. Over the coming seasons, our program will focus on evaluating nutrient management strategies that improve fertilizer efficiency, address emerging nutrient issues, and help growers adapt to changing production conditions. Building strong soil fertility foundations remains one of the most reliable ways to protect yield potential in Georgia cotton production.

Cotton production starts long before the planter enters the field, it starts with the soil. Strong crops start with strong fertility programs!