When does a water deficit affect cotton yield the most? According to a study conducted by Derrick Oosterhuis, professor of cotton physiology at the University of Arkansas and Dimitra Loka, doctoral graduate student at UA, cotton is sensitive to water-deficit stress at all stages of growth, but particularly during reproductive development, from first square to peak bloom.

Oosterhuis discussed the impact of water stress on cotton at Cotton Incorporated’s Crop Management Seminar, in Tunica, Miss. Here’s a closer look at what happens to cotton when water becomes scarce — both above and below surface.

Planting to emergence. “Water is critical for germination, noted Oosterhuis, “but prior to first square, there’s not much impact from drought stress or water stress on yield.” Oosterhuis noted that pre-irrigation at this stage “reduces the possibility of seedling disease compared to irrigation shortly after planting.”

At this stage, the most critical development of the plant is taking place under the ground, Oosterhuis noted. “Once seeds have germinated, there must be sufficient water for root proliferation. Often times, we don’t pay enough attention to roots. But it’s critical for us to understand what the roots are doing and where the water for the plant is coming from.”

Cotton seedling root systems develop early and rapidly during this stage, growing up to 2 inches per day.

Emergence to first square. Water demand at this stage is low, according to  Oosterhuis, but root development is still important. “The plant is partitioning a tremendous amount of its resources into the root at this time.”

Oosterhuis noted that unless the soil water deficit is extremely severe, irrigation during this stage contributes relatively little to yield.