By Rosalie I. Tennison
Vertical tillage conducted in the fall (minimal tillage).
December 1, 2014 - Despite the many advantages of no-till, some soybean growers are considering whether the benefits outweigh the disadvantages. It turns out that field trials conducted by the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), using several planting systems, showed little yield advantage between the systems.
However, one of the greatest issues for no-till soybeans is too much corn residue, which causes “yield drag.” Practicing good management can minimize yield drag, allowing growers to enjoy the benefits of no-till while growing soybeans successfully. According to Horst Bohner, a leading researcher on soybean tillage systems and a soybean specialist with OMAFRA, improvements in corn varieties have led to more residue due to yield improvements; and, while this is good news for corn growers, it has had a detrimental effect on the yield of no-till soybeans the following year. But, Bohner’s research offers some solutions.
“We see the bulk of yield development in soybeans in the second half of the growing system. Therefore, promoting early season growth is less important than it is with other crops. But, if plant establishment is poor, the yield will be affected,” Bohner explains. “If there is slow growth early on, it is largely due to the corn residue, which keeps the soil cooler and ties up nitrogen.” He adds that when soybean plants have to emerge through heavy corn residue, it results in poor plant stands and a reduction in yields.
In his field studies, Bohner compared no-till, minimum tillage and conventional tillage, along with two levels of corn residue removal, stalk chopping, use of a planter and a drill, and a nitrogen application. He says there is no one system that “fits all” – meaning growers have to determine which works best in their operation. However, with some management adjustments, soybeans can be grown successfully in each system.
“No-till is by far the most economical production system, as long as yields remain high,” Bohner admits. “But, you need to ensure you establish enough soybean plants for success and that means dealing with corn residue. Growers need to incorporate excess corn stalks, remove stalks, or chop them in order to allow the soybean plants to establish. Chopping corn stalks and leaving them on the surface can be a problem if they are not incorporated; or use a drill to seed into the stalks.”
There is also a geographical and soil type distinction that must be made when speaking about tillage for soybeans, Bohner adds. Northern counties, poorly drained fields, or heavy textured soils benefit more from some form of tillage. Fortunately, minimum tillage is usually sufficient. “There is no evidence a mouldboard plow is necessary in soybean production,” he says.
Bohner admits much depends on soil type, which can dictate what operations will be most successful. The costs increase as more tillage is done, so he cautions growers against only increasing tillage to solve the problem. In addition, much depends on the type of soil in the field, which could require further adjustments to ensure a healthy, well-established soybean crop.
“It’s important to note that in other long-term tillage trials, no-till operations have achieved higher soybean yield over the long term, if there are a lot of soybeans in the rotations,” Bohner admits. “No-till can also offer some plant health advantages because we see less white mould in this system and there is additional water retention.”
Growers need to determine how best to make their chosen system work, and then make the adjustments necessary to ensure top yields in every crop grown. Accepting lower yields in soybeans following corn does not make sense if the return on soybeans offers a greater advantage. Finding a balance is what is needed in order to grow all crops successfully.
“On average, we found that the difference between tillage systems is only about two bushels per acre,” explains Bohner, “but it could cost four bushels per acre to achieve that yield advantage. On occasion the advantage to tillage is four or five bushels per acre. In those fields it makes sense to conduct tillage. The hard part is identifying those fields.”
“In certain years, you may need to do some tillage in the spring because of what was grown in the field the previous year or because it is a wet spring,” he adds. “In particular, you need to get corn residue minimized to allow the soybean plants to get established.”
Bohner suggests growers need to consider using a row unit planter instead of a drill in heavy corn stalks. One of the main findings of the study was that a planter unit will outperform a drill, especially in chopped corn stalks. Or, if that is not an option, some form of minimal tillage can be a real aid to no-till drill performance.
Increasing the seeding rate is often recommended in order to overcome yield drag, but that may not be enough if the residue cover is too great. In most of Bohner’s trials over 10 years, no-till yielded very well. However, there was some improvement if corn residue was managed effectively. Although no-till yields were very good at most sites, Bohner admits there were certain fields where continual yield reductions, that could not be easily addressed, were noted.
Again, Bohner says his trials show there is some advantage to managing corn residue particularly when it is heavy, but growers need to decide if the time and energy required will prove advantageous in the long run. For growers who favour the no-till system and want to stick with it but are disappointed in the results of their soybean production, Bohner’s trials offer a way to continue using the system they want while getting yield stability. With careful management and some wise choices, yield drag in no-till can be minimized while continuing to reap the advantages the system offers.