Midway Extension District, Livestock Production

Grazing Crop Residues

Crop residue rental rates for the River Valley Extension District in 2015.
Crop residue rental rates for the River Valley Extension District in 2015.

With the current economic conditions of the agriculture industry, it is vital that producers explore all possibilities to meet the nutritional needs of their herd. Grazing crop residue in late fall and winter is one such opportunity.

When grazing crop residue, cattle will naturally select the grain first, followed by the husk and leaf. The cob and stalk will be the last choice. The nutrient profile of the plant parts differs. The average crude protein of corn grain is 10.2 percent while the cob has only 2.8 percent crude protein. As cattle continue to graze, the nutrient profile of the field changes with the differing levels of each plant part.

Many nutrient quality aspects described for corn can also be applied to sorghum. The grain sorghum leaf is generally higher in protein than a corn leaf, but sorghum grain is not as well utilized due to the hard outer coat of the sorghum berry.

Cattle grazing crop residues will consume 25-30 percent of the available residue in 30 to 100 days depending on the stocking rate.

Stocking rate influences the amount of residue available. Knowing the quantity of crop residue initially available and how much residue should remain to prevent soil erosion allows the producers to determine the quantity available for livestock consumption. The quantity of residue on the field can be approximated based on the harvested grain yield.

With high-producing corn, approximately 16 pounds of leaf and husk will remain per bushel of corn yield. For example, a field that produces 150 bushels per acre of corn will have about 2,400 pounds of leaf and husk on a dry matter basis per acre. If you practice the “take half and leave half” rule, there are 1,200 pounds per acre available for the livestock to consume.

One Animal Unit Month (AUM) is the amount of forage required to sustain a 1,000-pound cow for one month. It has been determined that a 1,000-pound cow will consume approximately 680 pounds of dry matter intake per month. Most of our cows today surpass the 1,000-pound threshold. If we consider a 1,200-pound individual instead, that would be 1.2 Animal Unit (AU) and she would consume about 816 (680 pounds x 1.2 AU) pounds of forage dry matter per month.

If the corn yield was again 150 bushels per acre, 1,200 pounds of husk and leaf would be available for consumption after taking into consideration the 50 percent rule. Therefore, the residue on this field would support 1.47 AUMs (1,200 pounds of husk and leaf on a dry matter basis per acre/816 pounds of forage per month required for a 1,200-pound cow) per acre for a 1,200-pound cow. That translates to 44 days of grazing (30 days per month x 1.47 AUM). As a general rule of thumb, one acre of irrigated corn stalks or grain sorghum stubble will provide approximately 1.5 to 2 AUMs of grazing.

According to a 2015 survey by the River Valley Extension District (Republic, Washington, Cloud and Clay counties), the average rate per acre for corn residue was $8.86 while sorghum residue was slightly higher at $9.00. On a per head per day basis, the average rates were $0.41 for corn stalks and $0.81 for sorghum residue.

It is important to keep in mind the possible adverse effect grazing has on the land. Grazing livestock can cause soil compaction, however compaction is generally shallow and temporary. Soil moisture as well as soil type are two of the main factors influencing the severity of soil compaction. Compaction problems are usually eliminated with the winter freeze and thaw cycle as well as spring tillage practices. A three-year study from the University of Nebraska indicates that fall and winter grazing has no significant effect on subsequent corn yields.

It is recommended for producers planning to graze annual forages to test the forages for nitrates. The Russell and Ellsworth Extension Offices provide this service to area producers. Also consider the nutrient profile of the available forage and different supplementation options.

 

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