With a little luck and some favorable weather, corn harvest should be getting wrapped up shortly, followed with turning cattle out to graze stalks. The ability to utilize corn stalks and other crop residues has always been a key part of being able to cost effectively raise cattle in this part of South Dakota. Frankly, I think that the ability to use crops and livestock to complement each other gives us a huge competitive advantage over many other parts of the country, and we owe it to ourselves to maximize that advantage.
There's been a lot of research done throughout the cornbelt showing that cattle will select a diet when that will run about 8% protein and 70% TDN as long as the more digestible parts of the plant are still in the field, such as the husks, leaves, and dropped ears. A diet like that will do a great job of putting body condition on a cow without any additional protein or energy supplementation, especially in mid-gestation and when she is not under any cold stress. We still need to supplement minerals and especially Vitamin A, but she'll be fine from an energy and protein standpoint.
As a rule of thumb, a stocking rate of about one acre per cow will let her find a diet of that kind of quality for 4 to 6 weeks. I've used the approach that if there is still corn on the manure, she's still able to select a high enough quality diet to meet her needs. If not, then it's either time to start supplementing protein or to move the cattle to a new field.
We do need to keep in mind that there is always the potential for grain overload if there is an exceptionally high amount of ear drop in a field. On fields that you know have more ears on the ground, I'd recommend limiting access, either by herding cattle in and out, or by strip grazing. At the very least, fill up the cows going to those fields with hay first to reduce the risk of grain overload.
What about the removal of nutrients from the field? The first thing we need to remember is the cattle will not take everything off the field. Under normal stocking rates cattle will eat about 10 to 25% of the residue and digest just over half of what they eat. A big wind storm will blow more husks and leaves off the field than what the cows would eat.
Will you sacrifice yield by grazing corn stalks? The University of Nebraska has been studying that question since the early '90s. They have not found any significant yield losses due to grazing in either a corn-soybean rotation or continuous corn. In fact a 14-year no-till study where the cattle were stocked at twice normal recommendations, soybean yields were increased 1 to 2 bushels the season following grazing, even when they ran the cattle into March when the mud would be the worst. I would think that if problems caused by compaction, organic matter removal or nutrient distribution haven't shown up after that many years with that kind of grazing pressure, that it's safe to say that grazing one cow on an acre for a month isn't going to cost yield. It may actually result in a yield bump, and that could be important if grain prices stay where they are now compared to the higher levels we've seen.
Reach Warren at 605-882-5140 or Warren.Rusche@sdstate.edu.