Preplant irrigation not just ‘fill ’er up’

For generations, irrigated producers on the Texas High Plains figured “fill ’er up” was the best way to preplant irrigate. When irrigation pumping capacity was more robust, specialists encouraged farmers to fill the top 3 feet of the soil profile.

Now, producers can’t splurge on preplant water. Ideally, fields would have full soil profiles going into July, but “banking” soil water by pouring it on before planting squanders the resource.

Key Points

• Research shows “recharging” profile with a pivot may not be an ideal solution.

• Preplant applications to fill soil profile yield less return than later watering.

• A change in management is needed as pumping costs rise.

“Under pivot irrigation, losses from wind and low humidity when preplant watering are huge. Less water may be used filling the soil profile following planting. Some prewatering as close to planting as possible may be necessary,” says Leon New, ag engineer and irrigation consultant with the North Plains Groundwater District at Dumas, Texas. “Filling the soil profile following planting provides an opportunity to receive help from rainfall and reduces system application and evaporation losses significantly.”

Cotton strategy

Jim Bordovsky, agricultural engineer and research scientist at Halfway, collaborated with Dana Porter, Texas AgriLife Extension Service agricultural engineering specialist, and Jeff Johnson, AgriLife Research economist, both of Lubbock, for the past two years, seeking optimum water use efficiency on cotton.

“It’s a fight to put water in the ground versus the environment trying to take it away. A high percentage of water can be lost in preplant irrigation with pivots. When a season starts dry and you’re trying to add water to the soil profile, things can get tough. With preplant irrigation, we’re exposing water to the environment a long time. Under low irrigation capacity, we have to start pumping earlier to get any water in the soil profile. High Plains producers clearly saw the detrimental effect of this during the past two years,” says Bordovsky.

He says overall pumping capacity during the growing season and potential water volume limitations, as well as soil water-holding capacity and the irrigation system type, all must be considered. “We don’t want cotton plants to suffer from planting to first bloom, but data from the past two years of field experiments show little gain from overwatering during that period. Excess water appears to be lost to the environment, or is immediately used to grow a large cotton plant that can’t be supported with available irrigation later in the growing season,” Bordovsky says.

Seeking maximum production per unit of water, Bordovsky and colleagues tested in-season irrigation levels from 0 to 17.6 inches in 2011. All plots received 3 inches of preplant irrigation using the LEPA method, and an additional 2 inches of water sprayed from the pivot to germinate the crop, for a total of 5 inches preplant.

Irrigation applied following the accumulation of 950 heat units, or following July 11, garnered more than 100 pounds of lint cotton per acre-inch versus under 20 pounds per acre-inch from units applied during the early vegetative period in 2011. During the drought of 2011, trying to store water above the cotton crop’s needs during June proved ineffective — a result also realized in the good rainfall year of 2010.

Steiert writes from Hereford, Texas.

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WATER WASTE?: Excessive preplant watering to build moisture in the soil profile may not be as wise as once thought. Texas cotton research showed better use of irrigation water when applied later in the season.

This article published in the November, 2012 edition of IRRIGATION EXTRA.

All rights reserved. Copyright Farm Progress Cos. 2012.