By: Wesley M. Porter, Extension Precision Ag and Irrigation Specialist
Cotton can be one of the most difficult crops to manage irrigation on throughout the season. Obviously, as with any crop, a lack of soil moisture will reduce yield. However, excessive soil moisture will reduce yields just the same, thus, a scientific irrigation scheduling method is strongly recommended to maximize yields and best match water requirements to irrigation applications.
As is typical, it has been a challenging year, especially from the perspective of water management. Beginning last September, we moved into a drought period and did not receive significant rainfall until recently. However, even with the recent rains, depending on which area of the state you are in, we are still behind on what is called a Water Balance. This may bring up the question of what is a “Water Balance”. It is calculated based on the amount of rainfall minus evapotranspiration. Simply put, we evaporate a certain amount of moisture everyday based on environmental conditions such as solar radiation, humidity, wind etc, and rainfall is our only way to replenish the evaporation. For example, if you use the UGA Weather Station Water Balance Calculator (Georgia Weather – Automated Environmental Monitoring Network Page) you can select a location and a time period and see where the water balance currently stands. For the Tifton Weather Station, from September 1, 2025, until June 22, 2026, we are at a -5.49-inch water balance or a 5.49-inch deficit. The entire state of Georgia is still classified into a D1 to d3 drought category. Thus, even with the rain, we need to remember that we are still in drought conditions.
The good news about the recent rainfall is that it has come at an appropriate time, especially if cotton were planted during May. Early May planted cotton is around 50 DAP and physiologically the crop planted during this time should be reaching the first flower stage. On average, the water requirements at this stage are 1.0 inches per week. The requirement will increase for about three more weeks or until the crop reaches the 3rd to 4th week of bloom. Peak water requirement corresponds with peak bloom and then drops off until cutout.
Even if you have a later planted crop, it is important to track crop age and estimated water requirements. As we are moving into an El Nino Enso phase, the near-term predicted forecast is for it to become dry again in July until late fall. While it’s never guaranteed either way, I suggest being prepared for a dry July and have a plan in place to ensure you do not fall behind on soil moisture during the critical periods. I would stress that currently, we have received more rainfall than we need for the crop. The downfall of this is that data have shown over-irrigation or excessive moisture will reduce the yield potential of cotton. This is because the plant will put more energy into biomass production than into fruit production. Thus, do not over irrigate the crop, especially with the recent rainfall we have been receiving.
It can be difficult to keep up with water requirements during peak bloom via irrigation alone so if it becomes dry during July, ensure that you have a scientific irrigation scheduling strategy in place.
The UGA Checkbook for Cotton water requirements is shown in Figure 1. The checkbook is a good guide, but it was developed based on a historical average ET across a 15-year average starting on May 1 each year. Thus, years that do not fall into the “average” category will not match the checkbook. Thus, I suggest using an irrigation scheduling strategy that helps you compensate for the seasonal variability that we observe every year.
As always, if you have any questions or need help with irrigation management on cotton reach out to your local UGA County Extension Agent.
Figure 1. Weekly cotton water requirements, with the corresponding growth stages.