Producers plant soybeans either back into cornstalks or wheat stubble—both very high residue crops that can present some special challenges for the next crop. Rarely do they plant soybeans back into soybean stubble—and if they did, they wouldn’t be faced with any residue management challenges as the amount of residue is minimal and its low carbon-to-nitrogen ratio means it will decay rapidly.
While lots of residue on the surface is good to prevent erosion and nutrient displacement, it also creates challenges. The problem is that excess residue will keep the soil cool and wet in the spring, immobilize nutrients during the decay process, cause hair pinning with the planter (residue gets pushed in the V-slot, prevents seed-to-soil contact and impedes proper placement) and can be a reservoir of soil-borne diseases.
No one will argue the benefits of keeping residue on the surface. It provides cover to absorb the impact of raindrops that causes soil particles to detach and erode with flowing rainwater. Residue recycles carbon and nutrients back to the soil and the next crop. It also sequesters carbon into the soil organic matter.
There are situations where no-tilling soybeans into cornstalks doesn’t work well. That includes continuous and high-yield corn that leaves a lot of trash on the surface, heavy soils that don’t dry and warm quickly in the spring, and northern latitudes in Illinois where there is very little fall and spring decomposition before the next planting season. Of course, exacerbating the problem is tough cornstalks that contain a Bt trait, have excellent plant health and don’t decay as fast in the field as a couple decades ago. While technology has improved standability, corn yields and decreased stalk rots, all that residue is a challenge.
However, as you go south in Illinois the situation reverses itself. Air temperatures stay warmer longer in the fall and warm up quicker in the spring. In addition growers are harvesting corn earlier, beginning in late August and early September. The more time you have in the fall with warm temperatures the more decay you will see. This is very evident after 30 or so days when the material begins to blacken, indicating it is decaying naturally.
Many Illinois growers manage cornstalks by tillage or chopping corn heads. The key to residue management is getting it to decay sooner and faster, and that can be accomplished by getting started earlier in the fall, sizing and slicing residue into small pieces, fracturing the outer waxy surface of residue to allow microbes to enter, and/or throwing some soil on top to both tie down the residue and introduce microbes into the plant material.
Some growers use more aggressive tillage with disks, rippers and chisels to accomplish this task, as well as work the soil. A newer category is vertical tillage, whose primary goal is to process residue and tie it down while leveling the seedbed and tilling the top 2 to 4 inches of soil vertically. Vertical tillage tools do an excellent job processing residue. However, with the heavy soils in northern latitudes, vertical tillage might not be aggressive enough to have the soil ready to plant soybeans next spring.
And cover crops might be one of the next tools to manage cornstalks. Decay is driven by natural fungi and bacterial populations. And cover crops create an environment that stimulate microbial activity. This hasn’t been researched thoroughly yet, but anyone who plants cover crops after corn will recognize that the material decays faster.
Lastly, we read a lot about spraying products on cornstalks. The most common is nitrogen and perhaps a little sulfur. Cornstalks have a very high carbon to nitrogen ratio and need some nitrogen to drive microbial decay. However, adding nitrogen to residue doesn’t always give consistent results. Other products today include spraying on microbes or enzymes (derived from microbes); most recipes require adding some nitrogen and carbon as a food source. While the science makes sense and the claims are enticing, do some testing to make sure you know if it works or not.
There is nothing better than seeing blackened stalks in the fall. When they get to this state they will fall apart come spring and make planting easier and the results more satisfying.
Let us know in our forum how you are managing cornstalks, if your strategy is effective in getting the material to decay and if your soybean stands are on target.
Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at firstname.lastname@example.org.