Dry times and what they do to the sorghum crop

When Josh Lofton was invited to speak for the Sorghum U/Wheat U event Aug. 11 in Wichita, Kansas, it was dry in parts of the High Plains. At the time he wasn’t concerned, but by August, his mind had been changed. Lofton is the cropping systems specialist at Oklahoma State University.

“This was in about late May. I was like, oh, it’s a little dry. Nothing we don’t experience normally right?” he said. “How things have changed and really, truly looking back on this year made it very difficult to for me to kind of think of what we needed to talk about here today.”

Looking at drought and sorghum, Lofton shifted his focus more to the agronomics and physiology side of what happens to sorghum during dry conditions or periods of limited rainfall.

Crops need water to survive and that water has been limited this year. Lofton looked at the eight-week change in the drought monitor index in Oklahoma. From June 14 to Aug. 11, the majority of Oklahoma has gotten significantly worse going through the season.

“The only reason why I think the Panhandle isn’t worse is because it was already bad to begin with,” Lofton said. “When you look at Kansas, it looks a little better, right? There’s a little less browns and yellows, but once again, I think they have a west Oklahoma problem.”

When there’s no water in the soil, you can’t get less water in the soil. Lofton has gotten a lot of comments from people across much of the sorghum production region, especially in the southern Great Plains and into northern Texas—throughout Oklahoma, Kansas, Colorado and western Nebraska—about how dry it is.

Some areas of the state aren’t nearly as dry as western Oklahoma, but Lofton said it has to do with the soil make up. The soils in eastern Oklahoma aren’t typically able to handle droughts like others.

Many producers went through the drought conditions in 2011 and 2012 and Lofton said every season provides an opportunity to learn.

“Look at what at least moderately worked and try to take something or as much out of it as possible because while this is something that next year we might not experience, I guarantee in the next 10 years we’ll probably have another one just like this year,” he said. “We need to take as much out of these kinds of years as we possibly can.”

Stepping back and looking at sorghum over all, it’s often considered one of the more stress tolerant crops out there.

“(It’s) important that we just don’t denote it to drought,” he said. “This is just overall stress.”

Sorghum typically goes on tougher ground—ground that is not irrigated—for a reason. It’s also a C4 crop or one that is adapted to life in dry, hot climates. C4 plants are able to separate the processes of carbon fixation and the Calvin cycle into the mesophyll cell and bundle sheath cells.

“(In sorghum) we do have this inherent natural means to attempt to minimize water loss in the leaf as we continue on with our respiration,” Lofton said. “This is basically the plant survival mode. Where it’s trying just to survive. We’re not gaining anything positively out of it.”

The term “low input crop” becomes a tricky one with sorghum. Some people define a low input crop as one where “we just don’t put anything out.” Lofton said that’s just not true. You just don’t throw the seed in the ground and walk away.

“How I interpret a low input crop—whenever you look at it and your resources are lower, so we’re talking about moisture, nitrogen, various other things—when you’re at a low level, the response of sorghum is significantly higher than most of our other crops,” he said. “So when we’re at the bottom of the barrel and we add something to it, the response of sorghum is much higher than, let’s say, it would be in corn.”

For Lofton, looking through the literature about sorghum, he’s found a couple matters that needed a little deeper look. There’s often misconceptions like sorghum being a drought tolerant crop, needing less water than corn, greater rooting depth, physiological responses, nutrient uptake, and stress recovery.

As for the lower water requirement, Lofton had some information from Kansas State University looking at water use from individual crops and how they respond with actual seed yield.

“When we digest them and we put some information to this basically, we see that when you compare crops—we’ll do corn and grain sorghum because that’s the easiest to kind of compare,” he said. “It takes about 7 inches in season to produce your first berry of sorghum.”

Sign up for HPJ Insights

Our weekly newsletter delivers the latest news straight to your inbox including breaking news, our exclusive columns and much more.

Whether that’s stored moisture, irrigation, natural rainfall, the first berry will start to be produced at about 7 inches of water. Corn takes 11 inches to produce the first kernel.

“We’re already at the deficit when you compare sorghum and corn we’re looking at a 4-inch benefit if you will, for sorghum compared to corn,” he said. “Okay, that’s a good thing, right?”

Not so fast. From that threshold above, it’s about 9.4 bushels per inch of water. Corn on the other hand, once it reaches that threshold with it’s higher yield potential and non-limiting environments, has a higher number.

“So it’s a little bit more efficient,” he said. “Once it gets going it just takes a while for it to get going. Okay, and then once you get above 20 in this corn’s going to be kind of in the superior because it has that ability that the higher yield potential.”

Lofton said it’s about a 150-bushel potential once it reaches that threshold.

“Sorghum kind of falls behind on its genetic potential and corn kind of just continues to take off from there,” he said. “This kind of gives the indication that potentially yes, sorghum does have that low water requirement.”

At Oklahoma State, Lofton said in irrigated studies Jason Warren, soil and water conservation specialist at OSU, looked at corn and sorghum in variety trials in the panhandle from 2005 to 2014. It includes drought years like 2011 and 12, but better years like 2007, 2013 and 2014. Those years didn’t require a higher amount of extra water to get by. In this set of data the average was about 238 to 240 bushels for corn. The highest yield came at 21 inches of water, with 200 bushels per acre. According to Lofton, 1 inch of water produces about 10 bushels of corn.

“Sorghum on the other hand, whenever you look at a non-limiting environment will typically yield less,” Lofton said. “On the high end, we’re looking at nearly 80 bushels lower. On the average, we’re looking at about 60 bushels lower. But we do that on about a third of the irrigation. Only about 8 inches on average.”

But when looking at the actual gain of bushels per inch of water, sorghum is quite a bit ahead.

“So whenever you start thinking to your yourself, ‘Is it less water?’” The answer to that is yes and no,” he said.

Lofton often hears sorghum is harder on the ground than any other crop, but looking deeper, sorghum normally is planted after wheat. If it doesn’t rain between sorghum harvest and wheat planting, most producers will still plant wheat.

“Because sorghum is so massive in its root and when we’re drought stressed—think about drought stress last year to where we had a big root mass,” he said. “We had big plants and then in August and September when the moisture kind of shut off, it was able to extract all of that water and those nutrients from those deeper soils.”

There’s a lot to consider but sorghum is not only hard on the water situation after wheat, but it’s also tough on nutrients. Phosphorus, potassium, nitrogen and micronutrients are going to even need to be higher than corn in some situations because of the root mass and break down the carbon.

“Plus if the nutrients are stressed and water stress and the P and K are low in that soil, sorghum is going to find it and it’s going to extract it with all those root hairs and those finally branch roots,” Lofton said.

The physiological response is very good and a lot more promising. Lofton hears the comment, “you don’t need any water to plant sorghum.”

“That’s just not true,” he said. “I got a lot of questions this year about I don’t know what I did wrong. My sorghum is dead. We didn’t do anything wrong. We didn’t get any rain for three months. I could have planted papaya out there, and it still would have died. Everything was going to die this year.”

It really didn’t matter what mile marker you were at, if you got rain you could grow a crop. He would see a field of really good sorghum and then a few miles away some that had already been rolled and baled.

Crop loss is going to occur in 2022—since moderate- to severe-drought stress is being observed—and he’s expecting about a 33% yield reduction. He never wants to see sorghum leaves rolling before the plant is headed out.

“Because why? We’ve got a long summer ahead of us and we’re already fairly drought stressed,” he said. “But when we do get moderate- to severe-drought stress on vegetative, we’re looking at reduction in panicle size.”

Panicle set occurs very early in the production cycle—around four to six weeks.

“So when you see these really small heads, more likely they went through drought stress a lot earlier in the year,” Lofton said. “Whenever you look at reproductive, more likely what you’re going to have a smaller seeds because just seed fill time got shortened. That’s what we saw a lot this year.”

Managing sorghum impacted by drought becomes crucial at certain times during the growing season. If the crop is really stressed and it happens to catch a rain and cooler temps, how will it end up responding?

“When do we start pumping that sorghum plant again to start harvesting that sunlight and putting more into the grain? That’s a big thing,” he said.

Sorghum can do a couple things when facing drought—survival, recovery, and avoidance, among others. Sorghum uses its root capacity to survive drought and water loss, as well as rolling leaves. The leaves roll in order to decrease the surface area and capture any humidity they can. A drought tolerant crop like sorghum is able to survive drought conditions, high temperatures and low humidity and still produce grain.

The most benefit from sorghum as a drought tolerant crop comes from its ability to fill an empty glass and pull off a good grain yield with less rainfall. Same with heat.

“It’s really able to tolerate some pretty high temperature some pretty low moisture to a point and timing is going to be that point—we have to be able to get into the rain is coming at the right time with good moisture,” he said.

Lofton reminds not to overlook fertility and pest management and be cognizant of keeping Johnson grass and crabgrass out of the fields.

“Good weed management, good fertility management is also going to be very key if we do run into a year like this (again),” he said.

Kylene Scott can be reached at 620-227-1804 or [email protected].