Patience a Virtue When Scheduling First Irrigation of Cotton

Mother Nature is sure taking us on a roller coaster ride in the San Joaquin Valley. It’s warm and sunny one day. Cool and rainy the next.

The unseasonably cool and wet weather lately has left cotton growers sitting on the sidelines, anxiously waiting to irrigate their young crop for the first time this season. Normally, the first irrigation comes around the end of May or the first week of June. This year, the first irrigation might be 7 to 10 days later than usual.

My advice to growers: Be patient. Scheduling your first irrigation too early could hurt you in the “bucket” at harvest time. Watering too soon will lower the soil temperature by 3 to 8 degrees and slow plant development and growth. It can lead to vegetative plants using up valuable nutrients and make it difficult to manage the crop. In the long, this translates into lower yields in the fall.

Looking at the 10-year average, we should be seeing 6 to 8 true leaves or nodes this time of the year. Today, I’m seeing plants at 4 to 5 true leaves, with some showing the 6^th leaf.

University of California researchers indicate the proper timing of the first irrigation is crucial and can boost yields by up to 400 pounds per acre. Air temperatures, wind and plant root development are among the factors that go into the decision.

As a general rule, growers schedule the first irrigation when moisture in the soil is six inches from the top. Currently, I’m finding moisture at 4 to 5 inches deep. We’re close to the irrigation threshold, but not there yet. We'll have to see what the impact will be from the rainfall over the weekend.

Bob Hutmacher, University of California at Davis statewide cotton specialist, reminds us this spring’s roller coaster weather requires growers to be vigilant about monitoring soil moisture and assessing root development in making irrigation decisions. A good ’ol shovel comes handy for monitoring, he says. To read about crop conditions and irrigation decisions, download a pdf (64.7 kb) of Bob’s recent Cotton Field Check publication.