LITTLE ROCK, Ark. -- Asian soybean rust is receiving a lot of well-deserved attention, said Chris Tingle. “It can be devastating,” said the Arkansas Extension soybean specialist. “But we don’t need to focus on this disease and forget about other problems.
“We’re not absolutely sure we’ll see Asian rust here, but I can guarantee you someone will be hit with stem canker.”
And don’t forget field drainage. Each year, much of the state’s early soybean crop is damaged from standing water.
“Drainage is one of our bigger problems in the state. Some have gone to bedded systems to try to address that. Through tests, we wanted to see if we could increase yields, because something like a twin-row system requires extra inputs. You have to purchase a planter or new drill. The vacuum planter — an 8-row unit — can cost $30,000 to $50,000. We want to know what kind of returns we can get from it.”
Creating twin rows on a single bed is very popular in some areas of Arkansas — “especially around Desha County on their black soils. It sure looks nice. The company pushing this said ‘kick your seeding rate up and you’ll see a significant yield increase.’
“Some growers asked if that was the case, so we put some tests together to find out. We couldn’t afford one of the high-cost planters, but we had a 7100 that allowed two rows on a single bed. Our rows were about 14.5 inches apart. The other system can get the rows 7 inches apart.”
Another system Tingle is seeing more of uses a fertilizer buggy or air-flow truck to sow seed on top of the ground. Its biggest plus is getting across acreage quickly.
“We did a lot of research on this back in the late 1980s and early 1990s when seed costs were down. Back then, you could get a bag of seed for $8 or $10. We had some seeding rates of 120 pounds. That wasn’t a big deal with lower seed costs, but with $35 seed now, is it really economical?”
Much of the research shows about 70 pounds of seed will give adequate stands for May plantings in irrigated conditions. With Roundup Ready varieties, “we’re spending about $40 to $42 per acre for seed. But we still have the benefit of the rows.
“Some growers have worked out a system to push down their seed rates to around 42 pounds. You can tweak this system as you go to fit your operation.”
Another method studied was simply drilling onto the beds.
“We were drilling the beds with the rows. But some growers have set their drills to go at an angle. The drills flex as they go across the rows and allow the use of all drill openings.”
In another study, 38-inch rows were planted on beds. “A lot of beans still are produced that way,” said Tingle.
In 2003, researchers saw a “pretty good” yield bump from the drill on beds. That finding was in line with previously collected data. The broadcast system came in a close second — “but you’re comparing 30 pounds of seed to 70 pounds. It’s easy to see which is more economical.
“The take-home message, though, was what we found with the twin-row system. It yielded adequately at 30 pounds. When we doubled the seeding rate, we got, perhaps, a bushel yield bump. Some growers who’d set up similar systems that year saw the same thing. The next year, we ran the trial again at the same location. We found essentially the same thing.”
If producers get out the right amount of seed — no matter how it’s planted — they’ll maximize yields.
“Now, these results focus only on yield. Other considerations — such as plant height — should be considered. Producers also need to consider their equipment options. Their current production systems may be sufficient from a yield standpoint, and the added expense of changing their equipment may not be justified.”
“We base seeding rates on the type of production system used. If you’re going in April — with favorable soil temps, some growers are planting in late March now — we like about 125,000 to 130,000 plants per acre in the final stand. Based on seed size, that’s 55 pounds to 60 pounds of seed. For the early systems, we recommend the increased seeding rates because we’re planting in adverse conditions: cold wet mornings, slower germination and emergence, risk of seedling disease.
We’re also planting more indeterminates — Group 4s, maybe some late Group 3s. Those don’t grow very tall. By increasing the seeding rate, we can make the plants grow taller, and that will help when harvest rolls around.”
Traditionally, producers have been told irrigated fields planted in May or June should have 100,000 plants per acre — 45 pounds to 50 pounds of seed. That’s the minimum population needed to achieve maximum yields.
“If you aren’t irrigating, you can cut the rate back 20,000 plants — 37 pounds to 40 pounds of seed. You need a final stand of 80,000 plants. That population, based on returns, maximizes soil moisture.”
With seed costs continuing to rise, Tingle said, “some cost-conscious farmers can tell me what a single soybean seed costs. It’s gotten to a point we need to fine-tune planting.”
Towards that end, Tingle and his colleagues wanted to make sure recommendations still hold for the newer, racehorse, high-yielding varieties. Test results show some of the varieties hitting 85 to 90 bushels per acre — almost double yields of 10 or 15 years ago.
“I constantly get questions about row spacing. We don’t separate seed rates from row spacing — it’s all based on plants per acre. A lot of old data told us 20-inch rows were our threshold and going with narrower rows produces a yield bump.”
All the beans for the tests were flood-irrigated and flat-planted. Researchers looked at seed rates from 10 pounds to 70 pounds and plant populations starting at 30,000 and moving up to 210,000.
“When we averaged the seeding rates across row spacing, we saw a yield bump on narrower rows, just as we suspected. When the rows are narrowed, we force the plants to gain height. On wide rows, branch pods can show up and that does help yield. But narrower rows encourage pods on the main stem, and that’s where data suggests the biggest contributor to yield comes from.”
Another question concerns the best planting date. Tingle focused mainly on Group 4s and Group 5s. Those varieties have become more adapted to Arkansas weather and soil conditions. Group 3s are getting better, “but they’re still unstable compared to the Group 4s. The Group 5s have always worked well for us — around 5.3 has historically made up the bulk of our acreage.
Tingle planted sets of maturity groups April 1 and planted them again every 10 days all the way to Aug. 1. “We tried to harvest those Aug. 1 beans a couple of weeks ago. But we were pulling plants — roots and all — through the combine. They wouldn’t thresh. We were trying to answer all the questions we could.”
After crunching the yield data, Tingle found the April and May planting dates are best.
“Yield is important, but we’re finding height is just as important on those early varieties. Some previous research claims test plots cut 65- to 70-bushel yields. But pay attention to what they’re doing: they could be harvesting a short plant by hand, picking up every pod. If we’re running a 20-foot header, we’re going to leave some pods in the field.”
Rust and early planting
When Asian rust was confirmed in the United States in November, there was much hype about early production systems.
“Some folks were claiming that was the way to go, that we’d be able to outrun Asian rust if we planted all our beans in April or the first week of May.”
A soybean plant is most defenseless when moving into reproductive stages. Often, that’s when pests or disease jumps on the crop.
“Think about it: if we plant indeterminates in mid-April through the first of May, those beans will likely enter key reproductive stages around the end of May or early June. If you look at the nighttime temps and humidity levels, that late May/early June window closely mimics Brazil’s environmental conditions.
“I don’t want to scare anyone, but for any disease to have an impact it must fit the disease triangle. You must have a pathogen, a host and the right environment. Even without disease, two of the three criteria are there during that June window: the beans are up in the right environment. If Asian rust has overwintered in the United States, we could get hammered in early plantings.”
If a producer plants beans early and rust doesn’t show up until September, he did the right thing. But no one knows if, or when, Asian rust will show.
“Try not to put all your eggs in the early basket — spread your risk like you’ve always done,” said Tingle. “Don’t let this rust dictate how you plant, go with what’s most productive for you.”