Estimating the Amount of Grain Left in the Field

Estimating the Amount of Grain Left in the Field
Estimating the amount of corn down in a field helps producers determine a grazing strategy. An 8" ear of corn contains about .5 pound of corn grain, therefore 112, 8" ears would equal 1 bushel. By counting the number of ears the amount of corn left can be estimated. If the corn is planted in 30" rows, count the number of ears in three different 100 ft. furrow strips and divide by two to get an approximate number of bushels per acre. Small ears and broken ears should be counted as half ears, while very large ears would count as 1.5.

If the corn is planted in 36" rows, then count the number of ears in three different 100' furrows and divide by 1.66. Any amount beyond 8-10 bushels per acre will require a well planned grazing strategy to ensure that too much grain is not consumed.

Grazing Cornstalks with High Corn Droppage

Now that the corn has finally dried down and producers are able to get cattle to cornstalks, we have had a few questions on how to manage stalks that have had lots of corn droppage. According to Staff at UNL, there are several strategies you can use when grazing Cornstalk fields with excess grain. These include...

-graze yearling cattle or calves first then follow with older cows

-graze cull cows destined for slaughter first, the follow them with the main herd

-short term graze (only a few hours per day)

-increase the stocking rate to reduce grain intake per animal

-divide the field into strips with power fence using polywire and fiberglass posts, forcing cows to consume some husks and leaves along with the ears of corn, this will reduce founder potential.

You can also fill the cows up with hay or other forages before allowing them to graze cornstalks.

UNL has put together a very good publication on grazing crop residues, you can find it at http://www.twinforksclinic.com/kevin/ec278.pdf Just copy and paste the link in your browser or just click the headline for this post and you will be directed to that publication.

Calculating Grazing Time on Cornstalks

Now that the corn is finally drying down, most producerers are getting cattle out to stalks.Here is a method of calculating the number of grazing days on a field of cornstalks. According to Dr. Rick Rasby at UNL, crop residue is related to grain yield. With high producing hybrids, there should be about 16 pounds of dry leaf and husk per bushel corn yield per acre.
Therefore, if a field produces 160 bushel/acre, then there should be about 2560 pounds of dry leaf and husk residue per acre. Now some of that residue disappears due to trampling and other factors so figure about 50% utilization, which leaves us with about 1280 pounds of grazable residue per acre.
Now we can convert our pounds of grazable residue to AUMs. An AUM (Animal Unit Month) is the amount of forage that is required to maintain a 1000-pound cow or equivalent for one month. It has been determined, that a 1000-pound cow will consume about 680 pounds of dry matter monthly. Therefore, this particular field will provide 1.88 AUMs/acre. If this field is 125 acres, then there is a total of 235 AUMs available for grazing in this field.
Now let’s assume we are planning on grazing 100 head of gestating cows on this field, we need to calculate the number of days that they can graze this field. Let’s assume the average weight of these cows is 1360. That means that each one of these cows requires 1.36 AUMs per month. Therefore, a total of 136 AUMs is required to feed this herd for a month. This field has 235 AUMs available for grazing so it should last about 1.72 months or 52 days.
Keep in mind that this calculation is just a starting point and is in no way a substitute for actual observation of residue disappearance. This calculation also does not figure in loss in stalk quality due to deteriorating weather conditions or just simply the natural deterioration that occurs over time.
There is also an Excel spreadsheet available for download online at http://agmanagerstools.com. Not only does this spreadsheet calculate the available grazing days using the same equation, but it also takes into account, the cost of the stalks, the cost of transporting the cattle to stalks, and the costs involved with checking the cattle and water. Kevin L. Cawthra, Animal Scientist, Twin Forks Clinic INC