Flooded and Waterlogged Conditions Impact on Cotton Management

by Bill Robertson, Cotton Agronomist - June 15, 2021

Producers in north Desha County received as much as 19 inches of rain last week. It’s the second-largest 48-hour total on record in Arkansas. They are in bad shape with thousands of acres underwater after this event. For some, the water drained but came back up. Some downstream who did not receive the record-breaking rain are now experiencing flooding because of floodwaters moving downstream. The cotton for some near Winchester is just now starting to have a healthier look and starting to grow (6/15). However, some report that floodwater currently is not receding very fast.

Waterlogged conditions reduce the crop growth rate by replacing the air in the soil with water. Clay soils can become depleted of oxygen after just 2 days of standing water. As roots become deprived of oxygen, plants are not able to maintain normal levels of respiration. Respiration is the process that the plant uses to provide energy and building blocks for growth. As soils are saturated and waterlogged, they become anaerobic. The effects on cotton plants may include chlorosis, yellowing, reduced shoot growth, reduced nutrient uptake, altered hormone levels, reddening leaves, and typical nitrogen deficiency symptoms.

Cotton can handle saturated soils for a short period of time. Typically, cotton roots grow 0.5-2 inches per day. Most of the root growth occurs the first 60 days after planting. In waterlogged soils, root growth slows, and roots will be near the soil surface where more oxygen is present. Reduced growth and shallow depth of the roots make plants more susceptible to drought stress later in the season. Monitor moisture in the zone where active roots are present. More frequent irrigations may be necessary with a shallow rooting zone.

For the cotton we are going to keep we must continue to evaluate insect and weed pests. Thrips and pigweed are here. A concern is that we will be tank mixing several chemistries that might be tolerated for the most part by a healthy rapidly growing plant but damage a weak slow-growing plant.  This will require more trips across the field to minimize additional delays to plant growth.  We cannot give up any more days.

Cultivation is an option used to address crusting that is often seen with flooding. However, producers should be careful when cultivating to minimize root pruning. Root pruning will further slow plant growth. Because of the impact on root growth and function, saturated soils also inhibit nutrient uptake, specifically phosphorous and potassium, along with nitrogen and other nutrients. An urge for some producers to do something may be to apply foliar nutrients to remediate observed or anticipated nutrient deficiencies. Foliar applications of nutrients may result in a slight improvement in appearance but are not likely to result in an economical yield increase as limited leaf area and slow uptake rates inhibit absorption.

Soil nitrates also can be lost from the soil once anaerobic conditions occur. As a result, supplemental N may be needed. For some, all the season’s nitrogen had been applied prior to flooding while others were about to make their final split. Do not add additional nitrogen beyond your planned rate now to make up for nitrogen that has been lost. If all the nitrogen has been applied prior to flooding, evaluate nitrogen loss and nitrogen needs as the season progresses and consider a supplemental nitrogen (approximately 20#N/A) application 7 to 10 days prior to cutout (nodes above white flower=5) or no later than July 20 to 25 whichever comes first. See the publication from Mississippi State University titled “How to Estimate Nitrogen Loss resulting from Saturated Soils”. The delayed nitrogen application will help ensure supplemental nitrogen goes to lint and seed production. Excessive nitrogen will delay maturity, attract plant bugs, complicate harvest aid programs, and further delay harvest completion

Generally, once waterlogged conditions pass, normal plant growth and nutrient uptake will resume, and nutrient deficiency symptoms usually will go away. Regardless, plants cannot compensate for lost time and crop harvest will be delayed as a result. However, cotton squaring today (6/15) is still on track to flower by July 4.

After the soil begins to dry out, there will likely be the urge to apply plant growth regulators (PGRs) to control plant size and possibly promote earlier maturation. However, we must keep in mind that waterlogged conditions also inhibit plant hormones, which contribute to growth and leaf expansion. So, be cautious about applying PGRs too soon after waterlogged conditions, because applications too early could further decrease the yield potential, especially for some varieties.

The 2021 season has been a challenge. The flooding and waterlogged soils will delay crop development. However, cotton can compensate for many adversities. So, do not give up on the cotton crop too early, timely management can still ensure a profitable outcome.