Dr. Benjamin McKnight
Extension Cotton Specialist, TAMU Dept. of Soil and Crop Sciences, College Station, (979) 845-0870
After a dry start to the 2021 Texas cotton growing year, most of the production regions around the state have received much needed relief to drought conditions. The Texas drought monitor maps from the month of April puts into perspective how dry conditions were across the state, with approximately 90% of Texas in some form of moisture deficit. Currently in July, approximately 90% of the state is not considered to be in any form of drought. Abundant rainfall experienced in May across much of Texas left many production fields inundated, in some cases for an extended period of time. These events left growers with several questions regarding cotton management following prolonged inundated or saturated conditions.
How long can cotton plants withstand flooded conditions?
First, let’s examine what is happening in the soil environment under these conditions. A main component to soils is pore space that is typically occupied by water and air. When these pore spaces are completely filled with water, little to no air, including oxygen, is present in the soil pore spaces. Oxygen taken up by the roots of a cotton plant is a critical component for plant respiration. Without oxygen, normal plant growth and development is hindered and one of the possible consequences can be a reduction in cotton root growth. From the time a cotton plant emerges until first flowering, root growth and development is rapid and often exceeds the growth of above-ground plant tissue. Root growth inhibited by these conditions can reduce the plant’s ability to take up water and nutrients from the soil, ultimately impacting yield potential later in season. Additionally, a poorly developed root system may potentially decrease the drought hardiness of cotton plants if soil conditions become dry later in the growing season.
As environmental conditions for normal growth and development return, regular nutrient uptake will resume and nutrient deficiency symptoms observed in flooded conditions should go away. Because soil nitrates can be lost as a gas under anaerobic conditions, additional N inputs may be warranted in some instances to satisfy cotton N requirements for yield goals. While cotton plants can tolerate extended periods of flooding, one thing the plant cannot recover is the normal progression of growth and development that was lost during the time spent in flooded conditions, in turn, delaying maturity and delaying harvesting activities.
When should I consider making a plant growth regulator (PGR) application after flooded or saturated conditions?
This is a question several growers have asked as conditions have improved well enough to get spray equipment back into the field. It’s natural to suspect that cotton plant growth will respond to the abundant moisture with a rapid flush of growth and the desire to be proactive with PGR management will be strong. Keep in mind that under flooded conditions the synthesis of plant hormones necessary for normal growth and development have also been reduced. As conditions improve, it takes the plant time to restore the synthesis of these hormones to normal levels. Applications of PGRs made too early before the plant can fully restore normal growth and development, or an overly-aggressive PGR application, may result in a decrease in yield potential. Active scouting following flooded or saturated conditions will help growers determine when the appropriate time is to make PGR applications. Additionally, many commercially available cotton varieties respond in different ways to PGR management. Seed company representatives will be able to provide recommendations regarding PGR management for each of their respective commercial cotton varieties.
How should I manage a non-uniform cotton field?
In many instances, fields that endured flooded or saturated conditions did not drain in a uniform manner. Areas of fields that are lower than surrounding areas remained saturated for longer periods of time, thereby increasing the time for cotton plants within these areas to recover and resume normal growth. I observed several fields in the Coastal Bend earlier this year that had plant height differences of 10 inches or greater. Managing a cotton field with variable plant uniformity can present additional challenges to normal management practices. Thoroughly scouting a field to determine which portion of plants in the same growth stage are going to contribute the greatest to yield will help growers determine which growth stage to manage for during the remainder of the growing season. Another factor to consider when making this determination is what time of year it is. Depending on location, the onset of tropical weather systems and remaining compliant with stalk destruction deadlines may be important factors to consider in the decision-making process. Additionally, keep in mind that cotton plants have the ability to compensate for space. While plants in some areas of a field may be delayed considerably more than others, they still may be able to capitalize on the remaining growing season we have left and positively contribute to overall final yield.