How long can crop residues be grazed?

Corn snow
A harvested corn field, with snow.

The harvest of corn and soybeans around the state of Ohio is coming to an end, and for most growers this is earlier than usual. As a young producer, I can’t remember a fall season like we experienced in 2022.

The mild temperatures combined with dry weather conditions allowed growers to harvest their crops on time without causing damage to the fields, such as compaction and rutting.

The yields this year were also not to be sneezed at. Sufficient rainfall and high heat during the growing season ensure above-average yields for both corn and soybeans. In my neck of the woods – in southern Ohio – disease and insect pressures were also low, ensuring healthy crops well into the second half of the growing season.

As a result, many growers are looking at freshly harvested fields full of residue – some may be tempted to start the tractor and hitch up the plow to deal with the residue; some may be tempted to pull out the baler and roll up the residue, and still others simply mow or chop up the stems. These are all very common practices and serve their purpose in certain situations, but they all have a common theme: they all cost you money.

With record high fuel prices and parts shortages, and if like me you have labor and time constraints, you might want to consider letting the cattle do the work.

Grazing crop residues can be a great way to extend the grazing season while reducing the amount of stored forage needed during the winter season.

Cons

Unfortunately, crop residue isn’t known for being the most potent feed in the feeder; they contain more fiber, little protein and lower digestibility. Another drawback is the infrastructure; in Adams County it is not unusual to find a spring water tank in the middle of a cornfield that is also completely fenced in, but in most of the state this is not the case.

Location can also be a disadvantage when grazing crop residues, as not every cropland is adjacent to your existing pasture, and loading livestock and hauling it 10 miles away isn’t the most exciting thing in the world.

Quality

With all that said, let’s just say you have a great opportunity to harvest some crop residue through livestock. You may be wondering how long the residue remains fit for livestock consumption? From the day of harvesting the crops, time starts ticking on quality and quantity.

So let’s deal with the quality issue first. Different crop residues will vary in quality, but for Ohio we usually deal with two main types of residues: corn stalks and soybean stubble.

Corn scraps can be broken down into multiple components, the stalk, cob, grain and leaves. The highest quality is in the grain and leaves, the lowest quality components are the cob and stem. On average, for all plant residues together, 6% crude protein and 40-45% dry matter digestibility can be expected.

Soy stubble can be very similar in quality, with a crude protein content of 4-6% and a dry matter digestibility of 35-40%.

Quantity

Quantity is the factor everyone looks at when it comes to grazing long and feeding less hay. The estimated amount of accommodation available for grazing is based on crop yield.

The University of Nebraska has great data that breaks down the amount of residue per bushel of grain yield, but in summary you can estimate 13-16 pounds of residue per bushel of yield. You can view the full details at beef.unl.edu/keys-corn-stalk-grazing.

My average corn yield for 2022 was estimated at 160 bushels/acre; essentially this means I would have about 2000-2500 lbs dry matter/acre to graze. There are many factors that can affect the ratio of leaves, chaff, cob and grain, such as hybrid varieties, combine adjustments and crop stability.

Now that we know the quality and quantity of the feed we have in the field ready to be harvested, it’s time to answer the original question to this article: how long can the crop residues be allowed to graze?

How long?

There are several factors that determine how long crop residues can be used as a feed source, including the following:

  • Weather: This factor will have a major impact on how long a producer can graze crop residues. As winter weather sets in, rain, snow, freezing and thawing of the soil can reduce the quality and degradation of the residue; remember we are competing with soil biology for food.
  • Types of Residues: Different crop residues will degrade in different ways because of their carbon-to-nitrogen ratio, which is the ratio of the mass of carbon to the mass of nitrogen in the plant structure. Crops with a lot of lignin will break down much more slowly because of the large amounts of carbon. For example, corn stubble is thought to have a C:N ratio of 57:1, compared to soybean stubble with a C:N ratio of 25-30. This means that soybean stubble is broken down much faster by soil microbes and weathering.
  • Livestock types: Different types of livestock have different amounts of food; The size and age of the animal also play a role in the intake. To all my meat producer friends looking for big, framed females, a 1400 pound brood cow consumes somewhere between 2.5 and 3% of her body weight, but because of the high amounts of fiber and the time spent sorting of the crop residues (look for the candy corn) it is thought that you can expect an average intake of 1.8% of body weight. This equates to about £25 per head.
  • occupancy rate: We know that our cows will consume about 25 kilos of dry matter per day and we have about 2500 kilos of dry matter per hectare available. But remember that about 50% of this residue will be consumed, which is equivalent to 1250 DM pounds available for livestock. With this information, we can adjust our stocking rates to get the most out of the residue through managed grazing.

Example: 1 cow of 1400 pounds = 1.4 animal units and consumes about DM 35 pounds/day or x 30 = 1,050 pounds per month. With available residue that will actually be consumed, 1250 pounds ÷ 1,050 pounds consumed per month = 1.19 animal units x 30 days in a month = about 38 days of grazing.

Let’s say you store feed calves weighing 500 lbs/head, 1400 lbs cow ÷ 500 lbs calf = 2.8 x 38 days = 106 pasture days available.

summarized

Crop residues can be a great resource for grazers looking to utilize unused feed materials and reduce stored hay consumption.

There are many factors to consider before beginning the grazing process, and supplemental feeding should be considered due to the lower nutritional quality of crop residues.

Crop residues don’t last forever, and many factors can determine how long the grazing period will last, but one thing’s for sure: Livestock doesn’t cost $5.00/gallon and you don’t have to worry about finding a part to graze . solve them. Happy grazing!

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