Last week, Frank Becker, discussed management of crop residue and the benefits and costs of various management practices, especially surrounding tillage. Today, I would like to address yet another management option for crop residue.
The phrase “grazing corn stalks” is a bit of a misnomer as livestock will select any missed grain first, followed by leaves, husks, then cobs. They typically will not graze the actual stalk until the more palatable and nutritious portions of the plant residue have been consumed.
According to several university studies, corn husks and leaves contain adequate crude protein (about 8%) and energy (estimated at 56% TDN on a dry matter basis) for non-lactating animals including pregnant livestock until late pregnancy. Livestock will still need mineral supplements when grazing corn residue.
In addition to the benefit of reduced purchased or grown feed for livestock, what animals leave behind in the field is a more readily available form of nutrients for next year’s crop. While healthy soil contains the necessary microbes, earthworms, and other creatures that help to break down residue, adding grazing livestock, which deposit manure, can speed up the process.
While corn residue is certainly not growing and cannot be damaged by overgrazing, the take half and leave half rule is still recommended. There are several reasons for this.
First, the latter half of what livestock eat is not as nutritious, as mentioned above. If livestock are forced to graze the stalks after the leaves, husks and even cobs are all gone, they will need supplemental protein and energy to avoid loss of body condition. Stalks alone are not an adequate feed source for any class of livestock.
Second, leaving about half of the residue will help to protect the soil over the winter until crops are established next spring. Thinking back to Frank’s article, we like to promote the “Goldilocks” mentality. There are sometimes reasons to remove all the residue or to leave all the residue. But, when in doubt, somewhere in the middle may be the safest option that promotes the best return to soil health, weed control, and field readiness in the spring.
The third reason to leave the stalks, or the 50 percent, is that during years of drought or excess nutrient uptake, the bottom third of the corn stalk can still hold toxic levels of nitrates after harvest. There is no danger in grazing the leaves, husks, cobs, or even top portions of the corn stalk when considering nitrate toxicity.
A couple things to avoid include grazing when muddy and grazing large sections of field with a proportionately small number of livestock.
Grazing in wet conditions damages soil structure and pushes edible residue into the soil, making it inaccessible and undesirable to livestock. It would be equivalent to plowing in the mud- which is largely frowned upon.
There is a trade-off between increased labor and more efficient grazing when considering paddock size. Smaller paddocks require frequent moving of fencing, water supply, minerals, etc. However, moving livestock and having them graze smaller areas each day increases feed efficiency and consistency. Also, in years when corn lodging is prevalent or equipment is not properly set up/older, a lot of grain can be left in the field after harvest. When livestock are turned out into a large area with free access, they will move around searching out those corn kernels and sometimes whole ears left in the field. This can lead to acidosis and other rumen issues.
To make things applicable to all livestock owners, one animal unit (AU) is equal to 1000lbs. This is roughly one cow or 5-7 ewes/goats, etc. Based on Nebraska’s “Corn Stalk Grazing Calculator,” a field that yielded 175bu/acre will have 1,400 pounds of available dry matter per acre when leaving half the residue. This would support 1 AU (1,000 lbs.) on 1 acre over a 2-month period. Grain yield is directly related to and affects available forage. Corn residue loses its feed value over time, so grazing earlier increases efficiency.
So, what is an appropriately sized paddock? If, for example, you have 25 beef cattle (~25 AU’s) and you want to rotate them daily, half-acre paddocks will work. If moving every other day, create one-acre paddocks. (25,000lbs. of livestock eating 2.5% body weight = 625lbs. daily x 2 days = 1250 lbs. consumed with 1,400lbs. available forage per acre.)
The above are examples only. Your yields and management practices may warrant different utilization or stocking rates if you choose to graze crop residue.
Matthew Nussbaum is an OSU Extension Agriculture and Natural Resources Program Assistant and may be reached at 330-264-8722.