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Irrigating Corn

We have finally gotten some much needed dry weather. This has really allowed us to finally get in our wetter fields and finish needed preparations for spring planting.
Most of our corn crop is nowhere near V8, but Dewey Lee’s point should be well taken. We need to make sure we take the time to manage soil moisture.  This was adapted from an earlier post by Dewey Lee.
By Dewey Lee, Extension Agronomist, University of Georgia,
 Little to no rainfall has fallen in the last week and weather conditions have been bright and sunny.  A good, well fertilized, healthy corn plant that is V7 to V8 is using about .2 inches of water per day.  Five days have passed and that usage would amount to 1 inch of water.  The holding capacity of a Tifton sandy loam soil ranges from 1 to 1.2 inches per foot of soil.  If you look at the root system of a V7- V8, it is quite extensive and therefore can explore most of the top soil.  However, if it sits in saturated conditions (water fills all the pores leaving no room for air), root growth is slowed due to low soil oxygen conditions. When it resumes, it likely has a slightly smaller root mass and thus will exhaust the smaller portion of soil it explores. Within this period of time, it can exhaust 5 to 6 inches of soil moisture and thus begin to suffer some stress.  Remember, this is an important time of developing the yield potential.  The number of rows is generally set during this stage, making it susceptible to loss of yield potential if the crop undergoes any stress.
Roots of a V7 plant that has exhausted the moisture in the top 5 inches of soil.
The plant in this picture (taken April 24,2015) comes from a field where moisture sensors are located.  The first sensor is set at 8 inches and shows us that there is still good soil moisture however, the roots are not fully exploring this area.  Upon digging near the row, you can tell that the soil is dry where the majority of roots (in this case 5 to 6 inches) are located therefore introducing the possiblity of stress.  Though the roots are beginning to explore the area below, it is not able to keep up with the demand.  If you were to conduct a soil squeeze test and check the soil at 8 inches, you could keep the ball of soil from breaking apart, however, this would not be true for the root zone. Remember, when irrigating corn its best to get out into the field and look at the roots and check the soil moisture in the root zone.
Squeeze some soil from the  area of interest and see if it will hold together.
If you are using the check book method, the scenario I have described will suggest some irrigation but in this case, sensors at 8 in. depth indicate there is good moisture.  Again, both are right.  Corn is a plant that is a little unforgiving.   Reducing stress is certainly the key to capturing yield potential and profit.  In this case, the leaves in the whorl were beginning to show a little stress. We certainly want to be wise with our resources yet in this case, when the plant is at a critical stage of setting the number of rows, I will irrigate ever time if I know that the plant is moving rapidly towards a stressful condition.

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