Arnall takes a closer look at small grain management at HPJ Live 

In agronomy, Liebig’s Law of Minimum is a common concept where the growth of an organism is limited by the one essential nutrient that is in the shortest supply, even if all other nutrients are abundant. 

For many farmers in the High Plains, water is often the first limiting factor. Other times, it’s a specific nutrient the crop needs. Managing all those elements together is key to a high yielding crop.

Brian Arnall, professor of plant and soil sciences, and precision nutrient management Extension specialist for Oklahoma State University, told attendees at HPJ Live in Wichita, Kansas, this summer, managing to win with a crop starts with expectations. 

Around Stillwater, at the university’s research plots, Arnall’s looking for 80-to-100-bushel wheat or 150-to-180-bushel corn. 

“Our soils don’t always support that, so if I know that I’m going high yield, I want 90-bushel wheat, 14% protein. I want good corn. I want 80-bushel beans,” he said. “And so, I am trying to push yield. I’m not trying to go with the state average of 40 bushels. I want to double or triple the state average. But water’s first.” 

Hours of daylight is a consideration in areas farther north of Oklahoma and Kansas, but in these two states, it’s not a problem. Soil conditions can make up for lost sunlight, Arnall said.  

“How much yield are we losing because we have even the slightest bit of a limiting layer in depth and old plow pan?” he said. “We have a lot of limitations, just because we don’t have topsoil and we have clay.” 

Much to consider

Arnall has been trying to question in theory and practice how applications, environment and other conditions can change his thoughts when it comes to making a recommendation to producers.  

“We need more grains per acre. That is an absolute fact. But where we get those grains—a lot of folks are thinking heads,” he said. “I want more heads per acre. I want to see all those heads out there. I want to see that thick canopy, at least in our environment, for Oklahoma.” 

However, having more heads in wheat isn’t always good and he said to think about it like corn. For example, when dropping 45,000 seeds per acre on dryland corn in Kansas, it may give a producer more heads and ears, but does it mean more grain?  

“Absolutely not,” he said. “With wheat does more heads need more grain? No. Heads fully filled out does.” 

Heads need time to fully mature and when they send resources elsewhere in the plant, that affects the grain fill in the head.  

“We’re trying to deal with the tiller that’s shooting up 3 or 4 inches, the berries are going to be 40-weight, and it will never stay in the combine.” 

Research matters

His recent work is “getting to the point” because he seeks fewer heads with grain filling out top to bottom.  

“More heads that are only 50% full doesn’t mean as much as one full head that gets every berry filled out top to bottom,” he said. “So there are some things we can do.” 

Theoretically, Arnall wants 62 million heads or spikes per acre or 61 heads per square foot. 

“This is the stuff that the data scientists come up with, managing tillers and with seeding rate, planting date, nitrogen—we can manipulate tiller count with all those things,” he said. “It’s not just planting date, it’s not just seeding rate, it is nitrogen, also all three of those. And in combination, we can manage tiller numbers appropriately.” 

Soil type needs to be taken into consideration with these sorts of recommendations, Arnall said.  

“It’s how much soil profile do you have that you can pull from if I’m deeper?” he said. “Be thinking if wheat is like corn—and I’m not talking grazers that’s another story—if I’m grain only, I should be treating it a lot more like corn. And think about how do I get that head as full as possible. And if I can fill one head, is there a chance to fill next one?” 

Points to ponder

Arnall said he was trained that as soon as the calendar hits Halloween, the seeding rate better start going up on wheat by Nov. 15. He would start around 75 pounds per acre if he was sowing in October.  

“Now. I’m not that way anymore. In fact, my October wheat is now going in at 60 to 65, but I still wouldn’t keep bumping as soon as I hit November,” he said. “You gotta compensate for the lack of tillers.” 

Arnall said with the data coming out of OSU, he’s confident many farmers over sow, especially later in the year.  

“We’re not necessarily losing yield by going to November,” he said. 

Sowing wheat in September or October versus November does show some difference in biomass, tillers and extra production.  

“What’s probably happening is we probably got more biomass out there that no one can support with rainfall,” he said.  

Cost considerations

Be aware of increases in seeding rates and what could be the possible outcome, Arnall added, especially with the high cost of inputs, seed and other factors going in the ground.  

“There’s no difference between the 60 pounds and 100 pounds, we want to start looking at proper costs with crop prices,” he said.  

Be careful with nitrogen when it comes to tillers. His research has shown that at least a 60-bushel-per-acre wheat crop comes from fertilizer applied—90 pounds of fertilizer per acre.  

“I want you to pump the brakes a little bit (when thinking about fertilizer and inputs),” he said. “It’s not good economics this year, but most years, that’s not bad economics.” 

Back to the wheat plant, Arnall has found that by delaying planting or applying fertilizer the plant is physiologically changing because of the stress. 

“When I say stress, I don’t mind yellow wheat in December. I don’t mind yellow wheat in January,” he said. “Honestly, little bitty wheat coming out of January is fine with me. I used to want row coverage by November. Now I don’t want row coverage until February.” 

He’s found that if there’s a “stunning crop” early that crop doesn’t have any luxury consumption through the fall and early spring. It’s usually a shorter time frame with less tillers. 

 “So, if we’ve got good ground, we got good potential early on. It leads to more growth, more opportunity for lodging,” he said. “So, it is slowing us down. It’s a shorter crop. It stands better by delaying that nitrogen into February March, reduced lodging.” 

When it is dry

Dry years also cause problems like wet years, according to Arnall.  

“If it’s a dry year, you’re also probably going to lose because you’re going to get that rank early fall growth, and it’s going to turn blue on you,” he said. “So, you hope that you have a good average year where you just have average rains, you don’t have any leaching potential, and the nitrogen stays right there for you.” 

To wrap up, Arnall said wheat growers need to know where their inputs are and where grain prices are to properly evaluate their situation.  

“We ought to get as much information as we possibly can from our field prior to making decisions,” he said. “That’s also why I don’t like pre-plant (fertilizer application) because I don’t know what the fall weather will be like. Let us get through fall and early spring, and then I can make my decisions on the big inputs, as far as nitrogen goes on that wheat crop because at least I’ve considered deeper samples.” 

He also suggested taking nitrogen samples in the field to make sure you know where you are with that. Reference strips in the field with sulfur, potassium, and other nutrient levels can be helpful too.  

“We’ve shown (in studies) in all crops that we can recover from stress. In fact, stress has been good. I’m playing with more and more stress,” he said. “Stress that crop early to make it seek more nutrients, utilize that root, utilize a shorter structure, and we have a lot of value with a little bit of crop stress.” 

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