It's common knowledge that no-till, glyphosate-resistant soybeans have allowed growers to plant earlier and farm more economically. But can such a system be sustained over the long haul?

Answering this question is the aim of research being conducted by Mississippi soybean specialist Dan Poston and research associate Brewer Blessitt.

Despite the obvious economic benefits of continuous no-till soybean production, problems in such systems have arisen, says Poston at the Delta Research and Extension Center in Stoneville, MS. Yields have dropped, weed pressure has increased and drainage problems have appeared, he says.

“We're concerned that a continuous no-till system using Roundup Ready soybeans with no pre-emergence herbicide may not be sustainable long term,” says Poston. “The yields have now plateaued, and other systems may be more profitable.”

Most continuous no-till fields are planted flat and internal drainage appears to be one of the most prevalent problems with this system, he says. In addition, disease pressure might be carried over from one season to the next from inoculum build-up in the residue, especially in monoculture soybeans. Buildup of weeds like redvine, annual grasses, groundcherry, dayflower, prickly sida (teaweed), glyphosate-resistant horseweed and pigweed has occurred in continuous no-till fields.

Poston's research, which began in 2006 and was repeated in 2007, looks at the potential benefits of using raised beds, deep tillage, surface tillage, fungicides and planting flood-tolerant vs. flood-susceptible varieties. All research was conducted on-farm, in a “real-world scenario,” he says, where continuous no-till Roundup Ready soybeans had been flat-planted for more than 10 years.

Poston says deep tillage and raised beds were obvious ways to boost yields at this location. No benefit was seen from shallow tillage or disking. “That's not to say we haven't seen a benefit to shallow tillage in other locations with other soil types,” he says.

Poston expects that some of the noticeable differences at other locations might be due in part to reductions in root-feeding insects, weed pressure and disease incidence, but he notes that more research needs to be conducted. Poston also notes that the four-row equipment used to establish some of the plots might have caused more compaction than wider implements used by producers.

“I was surprised at the yield differences between the soybeans planted flat and the soybeans planted on raised beds,” says Livingston.

While the promise of increased yields have piqued Livingston's interest in planting twin-row on raised beds, he likely won't be making any wholesale changes in 2008. Because he currently plants his soybean crop in 20-in. rows with a John Deere 7300 planter, converting to the new system would require at least two new pieces of equipment.

To calculate net returns in 2006, the researchers used a soybean price of $5.40/bu. In the 2006 tillage study, deep tillage improved yield by 11.6 bu./acre and improved net returns by $42/acre. The flood-tolerant variety P94B73 out-yielded the flood-susceptible variety by 6.3 bu./acre and improved the net return by $26/acre. Headline fungicide increased yields by 6.5 bu./acre and improved returns by $23/acre. In 2007, deep tillage increased yield by 7.3 bu./acre. Headline did not increase yields in 2007.

Poston attributes this to very dry growing conditions and extremely low disease pressure. “We had very little to no rainfall from May to mid-July and conditions were not favorable for foliar disease development,” he says.

In the 2006 study comparing raised and flat planting, raised beds increased yields by 9.3 bu./acre and improved net returns $47/acre, averaged across all treatments. Pioneer's P94B73 Roundup Ready variety was 7.4 bu./acre better than AG4403 and $32/acre better in net returns. In addition, treating with Headline increased yields by 3.6 bu./acre and improved net returns by $7/acre. All data have not been processed for 2007, but Poston did note that raised beds increased yield 17.7 bu./acre. “In 2006, we essentially controlled all irrigation because we received very little rainfall,” Poston says. He feels that three weeks of excessive July rainfall was the reason raised beds were so valuable in 2007.

“It's difficult to convince a producer harvesting 50-60 bu./acre with limited inputs that he might be leaving a lot of money on the table by taking a low-cost production approach,” Poston says. He notes that raised beds were an easily implemented improvement at this location and that beds could likely be used for more than one year at this heavy clay location. “This could allow us to use a minimum-tillage production system the second year and divide the cost of bed establishment over multiple years,” says Poston, who realizes that the major objection by producers to using raised beds is investment in new equipment. “Despite the initial investment cost, farmers cannot ignore an average yield increase of nearly 14 bu./acre over two years,” says Poston.

USDA-ARS soybean agronomist Trey Koger conducted complementary research in small plots using the same varieties and variables as Poston and has also seen yield benefits with raised beds. In his research, Koger observed 2 bu. and 7 bu./acre yield responses in 2006 planting into wide 80-in. beds and 40-in. beds, respectively. Yield responses increased when a flooding stress was imposed. Koger expects larger yield increases from raised beds in 2007.

“It all goes back to matching the right variety to the right field and selecting profitable inputs that increase profit and reduce risk,” says Poston. “Yield increases attributed to fungicides will generally, at the very least, cover the cost of the treatment and provide some protection against pod deterioration during wet harvest situations.”

Livingston adds, “This system seems to hold benefits for those growers who rotate soybeans with corn or cotton, but it may be more difficult to implement for those growers who rotate soybeans and rice.”

Poston and Blessitt will repeat their on-farm studies in 2008.

Survey Details

Darrell Livingston's Washington County, MS, farm was land formed at a 0.2% slope and watered by flood irrigation using wheel-track furrows to facilitate water movement. The soil is heavy mixed to clay.

Test plots in Livingston's field were planted in 40-in. twin rows with Group IV soybeans in early to mid-April and watered six times in 2006 and two times in 2007 beginning in late May. The grower improved his watering capacity by installing split risers, enabling him to water half of the field at a time.

Poston's on-farm research was split into two studies: one looking at no-till vs. deep and shallow tillage and another looking at raised beds vs. flat plantings. All tillage was done in the fall using a parabolic subsoiler for deep tillage and a disk for surface tillage. Both studies included a herbicide program consisting of glyphosate and 2,4-D for burndown in early spring, glyphosate again at planting, Sequence early post-emergence for residual control of pigweed and annual grasses and glyphosate plus Python in-season for teaweed control.

Headline was used on half of the research plots at the R3-R4 stage. The plot acreage also was split between two varieties — Pioneer 94B73RR, a somewhat flood-tolerant variety, and Asgrow 4403RR, which grows better in well-drained environments.

Plots were 700-800-ft. strips, four rows wide, with each test plot measuring about one-quarter of an acre. Each treatment was replicated four times to equal about a 1-acre field.