Corn harvest is already underway in some areas and you're probably seeing articles and advertisements on ways to help digest corn residue. The introduction of Bt corn with European corn borer resistance, improvements in plant health, greater stalk strength and routine use of fungicides and foliar nutritionals have all increased stalk strength and made stalks just plain tough. They decompose slowly, play havoc on tires and create challenges for planting next season. Managing corn stalks is more than just a challenge, it can be a real headache.
So how do we get stalks to decompose more rapidly and consistently and can we improve on or speed up what nature does naturally?
The requirements to get decay to occur include: cutting and fracturing residue to allow microbes to enter, the presence of microbes (and particularly white fungi that can break down tough cellulose in cornstalks), warm conditions (above 50 F), moisture and nutrients including soluble carbon, nitrogen, and sulfur. Fungi and bacteria also like a near-neutral soil pH (great than 6.2) and very low salinity (electroconductivity less than 1 dS/m). If any of these are missing or out of whack, microbial activity slows down.
Air and soil temperature are bigger factors in this equation than many of us realize. I have noticed over the years that in the Southern Corn Belt, stalks blacken in the fall within a month after corn harvest because it will stay relatively warm through October and into November. In the Northern Corn Belt, stalks usually remain golden brown in color till spring when the air finally warms up. It is just too cool in the fall for stalks to really decay much.
A healthy soil will have greater amounts of soluble carbon and nitrogen available than an unhealthy soil. Soluble carbon is what microbes prefer to feed on and having an ample supply will stimulate microbial activity when the temperatures are about 50 F. Injecting a band of anhydrous ammonia can kill off organisms in and near the band, leaving the zone inert until the ammonia dissipates in the soil and the microbes repopulate the zone.
Today the most common strategy to deal with tons of tough cornstalks is to shred, disk or disk-rip stalks, breaking them into smaller pieces and partially incorporate them into the soil. Throwing soil on the residue introduces bacteria and fungi that are the engines of decay. Some farmers purchase cornheads or roller attachments that chop stalks at harvest. There are also stalk stompers and rollers mounted on cornheads to knock the stalks over which helps fracture and put them closer to the soil surface. Vertical tillage manufacturers recognize the importance of processing cornstalks into smaller pieces, pushing it down to the soil surface and covering with a little soil as a way to get cornstalks to decay and they use this in marketing strategies.
While many growers feel that some form of tillage increases residue decay, a three-year study at Iowa State questions the practice. Mahdi Al-Kaisi, soil management specialist at Iowa State University, advocates that tillage doesn't improve soil quality or increase residue decomposition. He maintains that residue decomposition is a biological process greatly influenced by the environment (temperature and moisture) and soil conditions (pH, EC, structure and nutrient supply) and that tillage can actually compromise the soil conditions necessary to drive decomposition. Read that report here: http://bit.ly/…
Still, we know no-tillers and corn-on-corn farmers have special challenges. That's why many of these growers resort to spraying cocktails containing nitrogen, sulfur, humates, sugar or molasses, enzymes or microbes to speed up the decay process.
There are a couple of things you can do to assist nature in breaking down residue and you don't want to use tillage. You can plant some earlier-maturing hybrids and harvest in mid-September, which gives nature more time to breakdown residue in the fall. You can process the residue with a chopping cornhead or vertical tillage tool and put it on the soil surface so microbes can move it. I am not a believer that adding nitrogen and sulfur alone makes much difference, however also adding some molasses or sugar-based compounds may help.
Cover crops are getting a lot of publicity today to improve soil health and scavenge nutrients that otherwise might end up in surface waters. Leakage from these cover crop roots feed the fungi and bacteria and stimulates residue decomposition. Seeding covers with a drill, planter or broadcast and followed by incorporation, can also put the residue in closer contact with the soil.
When it comes to buying a residue digester product, know what you are buying: is it carbon, humates, enzymes, microbes or some combination of these products. Don't be afraid to do some testing before you commit your farm to these products. I'll be giving further explanations of these materials in my next column.
Dan Davidson can be reached at [email protected]
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