Planting dates and water use for sorghum in the southern Plains

Some compare sorghum and corn as apples to apples when it comes to water use in the southern Plains; however, at the recent Red River Crops Conference, Jason Warren, Oklahoma State University plant and soil sciences professor and water conservation management Extension specialist, explained how sorghum could be manipulated for more efficient irrigated water use by selecting the right planting date.

Grain sorghum prices are booming at the moment so farmers are looking into growing it more than ever, especially since it can complement certain crops in a rotation. However, the bottom line in the sorghum versus corn debate is that sorghum is just more cost-effective to grow.

“Sorghum is always more profitable per inch and that’s because the input costs are lower and seed costs are at least $50 less per acre,” Warren said. “You can spend $100 per acre easy on irrigated corn seed and you’ll only spend about $10 to $12 on irrigated milo seed and with the current distribution of price, milo wins in every situation. The gross revenue of corn is higher, but when you start thinking about net and how much it costs to grow 220-bushel corn, the milo wins because it’s just so much cheaper.”

Additionally, it can fit in nicely with other crops commonly grown in the southern Plains and adapts well to the climate.

“There’s a lot of opportunities for rotations depending on how the water situation is set up to share water, gain some residue and organic matter in some of the these continuous low-residue systems like soybeans and cotton,” Warren said. “One thing about milo is that it’s extremely resilient to drought and heat stress compared to corn and that’s why I like growing it as an insurance against some really rough times.”

However, one issue sorghum and corn share is that they require a lot of moisture and are often grown with irrigation.

“Milo requires as much water per bushel as corn and that’s a fundamental physiological fact, but the rooting depth and water stress recovery mechanisms make it much more efficient with irrigation water, especially under heat stress,” Warren said.

The question is, how much water does sorghum need and how can farmers plan out the growing process to use less water and support other crops at the same time? Part of the answer is planting time, which can affect the evapotranspiration or ET, which is the amount of water a crop uses through a combination of evaporation and transpiration.

“When we plant in April in Altus, Oklahoma, our peak ET is going to be about 26 hundredths of an inch per day and it is going to occur between June 16 and June 30,” Warren said. “In contrast, if we’re planting in June, it is going to occur at the end of the July and the peak ET will be 23 hundredths of an inch.”

This is important for when considering water sharing and the months cotton uses the most water.

“In July, we’re going to get into heavy irrigation of cotton and start to really push it so if we’re going to share water we need to consider what type of capacity is needed,” he added. “This 26 hundredths of an inch is about 600 gallons a minute that we’re going to be pumping to keep up with fully-irrigated milo. In contrast, we could get by with 350 gallons a minute if it was planted later and that’s what we see a lot in the Oklahoma Panhandle. They’ll plant milo in June and they can get by with a lower capacity on that milo because, due to the physiology of the plant, the peak ET is actually occurring before or during the booting stage and the plant starts to go into full reproduction afterwards.”

Additionally, Warren said planting in June means the ET during the early part of the season is about 0.1 to 0.12 inches per day due to evaporation of the soil surface. This planting time sets growers up to hit peak ET during the boot stage.

“There are two different times when we want to make sure milo is well-watered and that is at the growing point differentiation—about 30 days after emergence—and at the boot stage,” Warren said. “The reason for this is because at the growing point differentiation we can determine how many berries per head we have and at the boot stage if we have a full well-watered profile, it sets us up to go into flowering and really extra large heads to get them pollinated.”

On the flip side, early planting can offer some benefits as well. In fact, Warren said if he could plant sorghum in March, he would.

“If we plant at April 15, our ET is much lower earlier in the season with an estimated 0.06 to 0.09 inches per day,” Warren explained. “That’s the difference in evaporation between April planting and a June planting.”

Planting sorghum in April means the peak ET will occur after the boot stage, which determines how much water will be left in the profile after flowering.

“If we can plant it early, get it to boot or flowering and then divert water to that other summer crop. I’m not pumping so much water to get it to boot when I plant in April and if I plant in June I’m pumping a lot of water to get it to flowering, but it keeps the water profile full,” he explained. “With an April planting I’m pumping through flowering and my ET is going to subside quite rapidly and I will have an easier time keeping up with moisture demands.”

Finally, Warren said shorter season varieties are the best way to go when considering water sharing strategies, depending on how much grain you want to make versus cotton or soybeans.

Lacey Newlin can be reached 620-227-1871 or [email protected].