Mitchell County Ag News

Irrigation In Corn

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Our earliest corn in the county will be approaching tassel soon. There are lot of areas planted that are in need of some rain or irrigation. When corn progresses past V6 stage the amount water taken up everyday increases. Now is a critical time in crop development and yields are being established. Growers that wish to have high yields in their corn crop need to eliminate all periods of drought stress in order to achieve that yield potential.

Many growers may be using moisture monitors or other technology to determine when and how much to irrigate.  If you do not use one of these methods, consider using the checkbook method for scheduling their irrigation events. Below are tables from the “checkbook method” from the 2016 Corn Production Guide:

Corn Water Use At Various Growth Stages

EstimatedWaterUseInCorn-Table-10

Water Holding Capacities of Coastal Plain Soils

WaterHoldingCapacities-Table-11

Checkbook Method Example

This example shows how to use the two tables above and the “checkbook method” to determine when and how much to irrigate.

Step 1. The soil type of the corn field is a Tifton soil series. In Table 11, look at the average available water holding capacity in in/ft increments. Assuming a rooting depth of 24 inches (2 ft), the total available water is 2.2 inches (2 ft x 1.1 in/ft)

Step 2. The corn crop is 65 days old. From Table 10, the daily water use is about .31 inches/day

Step 3. Determine the irrigation by setting a lower limit of available water due to soil tension. For this example use 50% of allowable soil water depletion. In other words, only half of the water in the root zone will be allowed to be depleted. Therefore, 1.1 inches of water will be needed to replace the soil water that was either used or lost.

Step 4. Determine the amount of irrigation to apply by dividing the amount replaced by an irrigation efficiency. Assuming 75% as the irrigation efficiency, the amount of irrigation to required is 1.1/.75 = 1.47 or 1.5 inches.

Step 5. Determine the frequency of irrigation by dividing the amount of water replaced by water use per day. An example of frequency of water (either rainfall or irrigation) need: 1.1 in /.31 in per day = 3.5 days.

Step 6. Therefore, it is necessary to apply 1.5 inches of water every 3.5 days to maintain 50% available water for 65 day old corn.