Soil and water

Optimizing the use of irrigation in sorghum

I kicked off last month’s column by saying that I keep amazed how quickly fortunes can change. I was of course talking about market opportunities compared to previous years rather than soil moisture, as most of the sorghum belt was sorely lacking in the latter. However, my statement of rapidly changing fortunes is as true today as it was a month ago. Drought appears to be easing for now, and while anyone can guess how long this trend will last, the outlook is much better than it was just 30 days ago.

Not all areas are flush, and there are certainly some dry spots where the soil profiles are far from field capacity, and are therefore sensitive to drought conditions later in the summer. Considering this situation and the fact that the acres of irrigated sorghum are on the rise in 2021, I thought this would be a good time for a reminder on optimizing the use of irrigation water in the sorghum. As is usually the case when I write about agronomic issues, check-off sorghum agronomist Brent Bean has provided the intellectual firepower for the business. Thanks for your advice, Brent!

Watering plan

Sorghum is increasingly irrigated as a stand-alone crop in many parts of the sorghum belt, given the irrigation water drops we continue to experience on the Ogallala aquifer. It produces its first bushel of grain 4 acre-inches earlier than corn, and it has a greater ability to withstand heat and hold out moisture. However, it is most often used in situations where the irrigation water available is not sufficient for a fully irrigated maize crop, for example. In these cases, sorghum really shines, as it can withstand short periods of stress with little loss of yield while its companion crop is irrigated to its full potential.

For farmers in either situation, remembering a few key points will ensure optimal water use and yields. First, the available soil moisture should remain above 50% within the first 3 feet of the profile, but if the availability drops to 30% to 40% for a short time, yields are unlikely to be affected or only slightly reduced. Second, it is important to keep in mind that the timing of application is critical (especially for those sharing water between sorghum and another crop). Ear formation begins 30-40 days after emergence, so it is important to have good soil moisture for large ears with an increased number of berries.

Start-up step

After this milestone, the next key developmental stage is the boot stage, just before the head emerges. Much of the research done on sorghum over the years has clearly shown the importance of this step and that sufficient soil moisture significantly improves yield. Finally, as with corn, a full kernel fill profile will pack the starch in the berries, increasing both test weight and final yields. A good rule of thumb is to irrigate while the grain begins to color. After that, any additional irrigation will not increase the yield, but it could increase the strength of the stems and improve harvest efficiency in dry environments.

Whether irrigated alone or associated with another crop, sorghum is an increasingly judicious choice on irrigated areas. For farmers preparing their wells for the summer, keeping the above points in mind will maximize your chances of success. And as always, please don’t hesitate to contact me or contact Brent Bean if you have any questions. The bean can be reached at [email protected].

Duff is Executive Vice President of National Sorghum Producers. He can be contacted by email at [email protected] or on Twitter @sorghumduff.

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