Irrigation timing can affect everything from weed control to yield and fiber quality, according to an on-farm study by Tom Barber, Extension cotton specialist for Arkansas, Phil Tacker, former irrigation specialist at the University of Arkansas and Paul Francis, agriculture professor at the University of Arkansas at Monticello.

The study, funded by Cotton Incorporated, looked at three initiation timings, two weeks prior to bloom, a week prior to bloom and at bloom. Several termination timings were also included — 300 heat units after cutout, 450 heat units after cutout and 600 heat units after cutout.

The study is based on research that once cotton starts squaring, demand for water begins to increase, climbing as the plant reaches bloom and peak boll fill.

Barber noted that irrigation research in the Mid-South is more difficult because rainfall can be so scattered, even in a single field. “We did have weather stations on the fields, but it was impossible to record every inch of rainfall that falls on a farm.”

The research was conducted on a 160-acre field belonging to producer Steve Stevens, in Tillar, Ark., and included both silt loam and silty clay loam soils. The variety planted on all the plots was ST 5458B2RF. Rainfall was variable during the course of the research.

The irrigation method was furrow, and researchers used the PHAUCET (Pipe Hole and Universal Crown Evaluation Tool) which helps farmers improve timeliness on fields with different row lengths. “It’s a great tool for saving water and preventing runoff,” Barber said.

Watermark soil moisture sensors were also used in the three year study which concluded in 2010.

The research indicated that much more plant structure was built by bloom with an early, (two weeks prior to bloom) initiation of irrigation versus late initiation. In terms of plant structure at bloom, there was no difference between plots where irrigation was initiated a week prior to bloom and two weeks prior to bloom. However, by the end of the year, the earliest initiated irrigation was ranker than the later timings.

An early initiation did hasten canopy closure, noted Barber. “This is important for us because we’re not only watering the crop, we are fighting resistant pigweed. If we don’t get that canopy closed early, and the sunlight hits the furrow, we’re not in a good position to control them.”

Barber noted that the crop did not canopy in any of the treatments in which irrigation was delayed to bloom or later.