Proper irrigation is a science, but implementing it on-farm is less precise.
Crop moisture serves two purposes: it cools the plant and transports nutrients needed for development. When nature doesn't provide enough water through rain, irrigation systems can compensate.
Jim Thomas, agricultural engineer with the Mississippi State University Extension Service, says there are no fixed initiation or termination dates for irrigation in Mississippi.
“You need to know the needs of the crop, the soil moisture status and the crop stage of growth. Then trust your instincts,” Thomas says. “If you wish your fields would get an inch of rain, then it's probably time to turn on the irrigation.”
In Texas, cotton farmers start irrigating at square set and continue until they can no longer meet crop demand from the soil and supplemental irrigation. In Mississippi, cotton farmers usually start irrigating July 1, or around first bloom. They usually terminate the irrigation in mid-August, or within two weeks of the first open boll.
Mississippi producers usually do a better job with furrow irrigation than with pivot irrigation, says Thomas.
“We typically don't put out as much water with pivots as we do with furrow irrigation,” he points out. “We turn the pivots off after three or four days because the ground looks wet. But pivots are usually designed to meet daily crop demand for water and should be run 24/7.”
Thomas recommends producers with pivot irrigation make at least three circles, and then check soil moisture in the field. On average, three circles are equal to one furrow irrigation.
“Pivot irrigation making a three- to four-day circle on a four- to five-day return cycle gets 80-85% of the water to the plant, and only meets 60-65% of the plant's needs,” Thomas says. “Cotton irrigated with a pivot three days out of seven can run a deficit for three days or more on average.”