Be Proactive and Hope the Weather Cooperates
Soybean germplasm possesses a lot of untapped yield potential, says Farm Journal Field Agronomist Ken Ferrie. But there’s no cookbook recipe that is guaranteed to bring it out.
That’s because so much of soybean yield is based on environmental conditions. The high soybean yields experienced by many farmers in 2010 may have resulted from unusually good growing conditions.
However, Ferrie explains, "We’ve seen things in our 20 years of on-farm studies that make a difference in yield and do it consistently enough that we know we should pay more attention. They help set the stage for maximizing yield when the environmental conditions are right."
Ferrie shared those tips with attendees at Farm Journal’s 2010 Corn College, which featured the first-ever soybean bonus session. (Learn more about Soybean College.)
1. pH is critical.
Don’t let soils get acid. "Soil pH is an important factor with soybeans," Ferrie says. "As soon as we let pH slide, we run into trouble."
It’s their root system that makes soybeans so sensitive to acidity.
"Instead of grassy roots, like corn, which spread out through the soil, soybeans have a taproot concentrated in one area," he explains. "The roots release hydrogen, which creates an area of concentrated acidity around them."
You may have observed this effect without realizing it if you ever planted soybeans in an alkaline field with a high soil pH. "During dry periods, the soybean plants look green and healthy because the acidity produced by the roots counterbalances the alkalinity of the soil," Ferrie says. "But then you get a rain, which washes the acidity deeper into the soil. The soil becomes alkaline, nutrients are tied up and unavailable and the soybeans turn yellow."
Acid soils will have poor nutrient release; regardless of what your soil test says, you won’t get nutrients into the plant. Acid soils will kill off the rhizobium bacteria, which are responsible for nodulation.
"Your soil may be at a marginal pH of 6.1 in mid-April; but if it gets hot and dry in June and July, your pH could dip in the zone around the taproot," Ferrie adds. "That acidity will shut down the soil microbes.
"Keeping soil pH in the sweet zone results in more consistent soybean yields," he concludes.
2. Manage alkaline soils.
Alkaline soils are prone to micronutrient deficiencies, which can have a critical effect on yield, Ferrie says. "In some calcareous, high-pH soils, it might be best to take soybeans out of the rotation. If you decide to plant soybeans, find a variety that can handle that situation."
3. Balance fertility.
Potassium plays a big part in soybean yield because it is involved in water management and disease prevention.
Keep an eye on magnesium levels, especially if a field is high in phosphorus—for example, from overapplication of manure. "If soil magnesium levels are low, we tend to see magnesium deficiency in soybean plants," Ferrie says. "You may need to make an application of K-Mag or dolomitic limestone to fix the problem."
4. Nitrogen probably won’t help.
Think carefully before you apply nitrogen fertilizer to soybeans. "Applying nitrogen in the spring may make soybeans look good because they usually don’t produce their own nitrogen until the third to fourth trifoliate, but it usually has little effect on yield and sometimes lowers it," Ferrie says. "Typically, having excess nitrogen available makes soybeans lazy about nodulating and producing their own nitrogen.
"Starter nitrogen may give beans an extra push in late planting, stressful situations or cold soils. But, in general, concentrate on phosphorus and potassium. You need phosphorus for cell elongation and growth and you need potassium for disease resistance."
Soybean seeds are sensitive to fertilizer burn, Ferrie points out. So if you apply starter, place it to the side, rather than in the furrow.
5. Foliar feeding? Maybe.
For certain soils that are deficient in manganese, foliar feeding can prevent deficiencies in soybean plants, Ferrie says.
6. Plant beans like corn.
Plant soybeans 1" to 1½" deep. Try to plant at the correct time—when soil temperatures are above 55°F in the Corn Belt or by the calendar if you farm in the South. "If you stick beans into cold, wet soil, you probably will be replanting," Ferrie says.
Set your planter to do a good job of singulating because you’ll likely get a more uniform pod load, which is important to yield.
If you do have to plant in tough conditions and get a less than ideal stand, don’t give up on the crop—soybeans have a remarkable ability to compensate. "Because soybeans set their yield later in their development, a tough start for beans doesn’t carry the yield penalty that it does for corn," Ferrie points out.
7. Planter box fungicides.
Know the type and amount of disease pressure you face in each field. "If a field has a history of water molds, such as Phytophthora and Pythium, treat the seed with a fungicide," Ferrie says.
8. Inoculate seed.
If a field hasn’t grown soybeans for a few years, inoculate the seed with rhizobium bacteria. Ferrie’s studies have shown that inoculating does not always increase yield. In some situations where water runs across a field, the soil may get reinoculated automatically. But if an inoculant is needed, the payoff can be great. "An inoculant is too cheap to leave out," Ferrie says.
9. Stay ahead of pests.
Because pest management is such a critical part of high soybean yield, designate a pest boss on your staff or hire a consultant to scout fields.
You or your pest boss must know the critical stages in soybean and pest development and the economic thresholds for treatment. Stay on top of diseases and manage them with fungicide application, rotation and varieties.
|Current soybean prices provide even more reason to pay close attention to your pods.
Photo: Beth Snyder
10. Nix on nematodes.
"Soybean cyst nematodes are the biggest pest we deal with," Ferrie says. "Once you have them, they are almost impossible to eliminate. Rotating to corn for one year cuts the population in half, but even with more years of corn the population never gets much lower.
"If you continue to let nematode populations build up, you will lose four to five more bushels per acre every year. In no-till fields, you can help keep populations in check by applying a burndown herbicide in the fall to control perennial weeds that serve as hosts to nematodes. Plant resistant
varieties and rotate to non-host crops when possible."
11. Rotation pumps yield.
Rotation almost always promotes higher soybean yields, Ferrie says. "It’s the most consistent yield factor of anything we have studied, on every soil type. In our trials, rotating to corn for two years increased soybean yields by 5 bu. per acre. Three years of corn boosted bean yields by 7 bu. per acre, and four years of corn resulted in a 10- to 15-bu. yield increase."
12. Fix compacted layers.
"It’s much harder to get tillage responses in soybeans than in corn," Ferrie says. But that doesn’t mean beans like compaction, he adds—it just means they are better at coping with it, especially if rain falls at the ideal time, during the reproductive stage. "While removing compacted layers may help soybeans, it will definitely help the corn you plant next season," he says.
13. When stress helps.
Stressing plants may be a good thing—if you understand what you’re doing. "Sometimes you can burn soybeans with diphenyl ether herbicides, such as Cobra, and get yield response, and sometimes not," Ferrie says. "In our plots, if we spray the herbicide under the right growing conditions and at the right time, and burn the main bud, we can trigger the plant into branching and setting more nodes and more pods, and shorten the plant as well. That response increases yield."
14. Don’t waste seed.
"It’s hard to increase soybean yield by pushing population to the extent that you can with corn," Ferrie says.
From 1992 through 2007, Ferrie compared seeding rates of 120,000, 160,000 and 240,000 viable seeds in row widths of 7½", 10", 15", 20", 30" and twin rows.
"From those results, 120,000 would stand with or beat most populations in 10" and 15" rows," he says. "In 20" and 30" rows, the results were less consistent, but the worst population usually was 200,000 or higher."
In 2008, a notoriously late spring when soybeans were not planted until the last day of June, things were different. "The 200,000 rate still wasn’t the best, but for the first time, 120,000 fell short in all row spacings," Ferrie says. "In 2008, the 120,000 population got hurt worse in 20" and 30" spacings than in narrower rows.
"That was because of the June 30 planting date. The indeterminate soybean varieties went into the reproductive stages too quickly, and we got short plants. The lesson is that if you are planting late, you have to kick up the population. After all, you don’t double-crop soybeans at 120,000 plants per acre."
15. Don’t leave yield in the field.
Careless harvesting can knock bushels off that high yield you’ve worked so hard to produce. Adjust your combine’s speed, concave clearance, cylinder speed and air velocity to conditions in each field. Keep knives and ledger plates sharp.