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Early-season corn irrigation

LITTLE ROCK, Ark. -- Arkansas corn acreage is estimated to be as much as 450,000 acres this season. By April 25, some of the corn will have been up and growing for three weeks or more.

Corn's daily water needs are relatively low (0.05 to 0.10 inch per day) in the first three to four weeks of vegetative growth, and rainfall usually meets the water demand during this period. However, if the crop emerged in pretty dry conditions and rainfall has been scarce in the first three weeks, irrigation may soon be needed.

Corn's vegetative growth stages are determined by the number of leaves having a leaf collar that is a visible, light-colored, narrow band at the base of the leaf. When corn has six to eight fully developed leaves (see figure) it is usually about knee-high, and the growth rate is set to rapidly increase.

The number of kernel rows per ear is determined at this time, so moisture stress should be avoided.

A side-dress fertilizer application is usually made prior to this time to meet the plant's increasing water and nutrient needs. Irrigation is often needed to activate the fertilizer and prevent moisture stress. This is especially important if the corn has a limited root system because of poor drainage and/or cool soil temperatures.

I hope your irrigation system is ready to go so the corn can be watered if you don't get a timely rain at this stage.

Pivot systems provide a good method for watering-in fertilizer and controlling the amount of water that is applied. A 1-inch irrigation usually avoids runoff and keeps the field from becoming too wet from rain soon after the irrigation.

Pivot irrigation should not be delayed to the point that the plant starts using the deeper moisture. This needs to be protected for the plant to tap into later in the season when water use can be 0.3 inch per day and it becomes difficult for the sprinkler to keep up.

Those who levee water know that it should really be a flush method to get the water across the field as quickly as possible. This is difficult on big, flat fields unless it is possible to put in a cross levee for better irrigation management on two smaller fields.

If this isn't practical, then providing multiple water inlets to the field can be helpful. A canal or flume ditch alongside the field can provide multiple inlets, but irrigation tubing may also be used.

The top levees can be watered from the pump discharge or riser and the tubing can be used to water the bottom levees. Some growers find that it helps to put spills in the levees so they don't have trouble building the levees back in time for the next irrigation.

I hope levee-irrigated corn is on a bed so it is less subject to potential problems if the field stays wet for longer than desired.

Some furrow irrigators consider watering every other middle on the first irrigation since the chance of getting rain at this time of the season is usually pretty good. Unfortunately, the middles usually become sealed over after a couple of irrigations causing water to move too fast down the field and not soak into the beds.

This factor and the labor required with plugging and unplugging the tubing is why most growers run parallel tubing lines across the field. This allows them to water each middle and better manage the multiple sets required to get across the whole field.

More information on corn irrigation and production is included in the new Corn Production Handbook, MP 437. The Arkansas Corn & Grain Sorghum Board funded its production and copies are available through Arkansas county Extension offices.

If you have questions or suggestions on topics please contact me: Phil Tacker, 501-671-2267 (office), 501-671-2303 (fax), 501-944-0708 (cell), or [email protected] (e-mail).

Phil Tacker is a University of Arkansas Extension ag engineer.

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