We have been dry here for the last few days and most area corn fields could use some water. Most of the corn in the area is at growth stage v6 or bigger and is in that very critical stage of growth when the yield potential of the crop is being determined. Growers that wish to have high yield potential 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 are not using one of these methods, growers should consider using the checkbook method for scheduling their irrigation events.
The following tables and “checkbook method” example are from the 2015 UGA Corn Production Guide. You can find the entire guide at the following link: http://www.caes.uga.edu/commodities/fieldcrops/gagrains/documents/2015CornProductionGuide.pdf
Corn Water Use at various growth stages
This table shows the water use of a corn crop and different growth stages.
Water Holding Capacities of Coastal Plain Soils
This table shows the water holding capacities of some of the common soils in the area.
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.
If you have any questions about using the checkbook method to schedule corn irrigation, contact your local county agent for more information.