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July Irrigation Thoughts

Things are hot and dry in the county right now. Minimal rain, if any, has fallen in parts of the county recently, so irrigation has been running. Hope to see more rain soon – keep praying!

Non-irrigated cotton in wilt
Non-irrigated peanuts (hoping to catch some rain from this pop-up shower)

Following is a summary on July irrigation from the UGA Irrigation Team members (Dr. Wes Porter, Cale Cloud, and David Hall).

COTTON – Cotton that was planted during May in Georgia should be squaring by now and approaching bloom, if it hasn’t already began blooming. Bloom occurs roughly 9 weeks after planting and water requirements really ramp up and approach peak demand during this time. Irrigation requirements and demands are very critical during the “First flower to first open boll” period of development. This growth stage takes place during weeks 9-17 after planting. Thus, based on when your cotton was planted, you will probably
enter peak demand during the month of July. During this stage, cotton may require up to 1.5 inches per week or 0.2 inches per day. Keep in mind that the Soil Water Holding Capacity of most of our soils is around 1.0 inches/foot of soil. The crop can only access water where it has roots and of this SWHC only about 50% of it is plant available. Thus, a cotton plant with an 18 inch rooting depth will have access to 0.75 inches of water at field capacity, meaning it will require irrigation every 3 to 4 days minimum based on rainfall and irrigation efficiency during this stage. It is important not to let your cotton crop experience water stress during the flowering stage, as stress during this stage can reduce plant growth which in return can reduce the number of fruiting sites that are initiated.
The main thing to keep in mind is that these water requirements are based on a historical average and that the crop may not necessarily need or use the amount of water as shown in the graph below. If you have cooler and cloudier or more humid days, your crop may not use nearly as much as it would if it would on a hot, sunny, and dry day. The graph below should give you a good idea of your weekly water requirements through the month of July IF you planted between mid-April and mid-May.

PEANUT – Most of our peanut crop in the state should be pegging and putting on pods by now and approaching peak water use. Please refer to the graph below to indicate where you are at with weekly water use in your crop. Remember this requirement is IRRIGATION and RAINFALL! Once peanuts begin blooming and pegging, they will use roughly 0.2” of water daily for ~20 days. By the middle of July, those early/mid May planted peanuts can use up to 0.3” of water per day, so it is important to not get behind on irrigation. It is also important to not let your soil temperature get to high with peanuts pegging. High soil temperatures can burn off pegs. If you are using a computer based scheduling model such as Irrigator Pro, it has a maximum soil temperature notification that will alert you whenever your soil temperature reaches threshold, informing you that irrigation may be required to cool your soil temperature, even if there is adequate soil moisture.

CORN – Much of the corn in the county is nearing full maturity (black layer). Some of the later planted corn is in the milk stage or beyond. Click here to see a recent article from the blog on “Irrigating Corn” (July 10, 2020).