The five-year average of corn acres harvested reported by NASS leads to an estimate of approximately 5.5 million acres of corn and 200,000 tons of residue produced annually in Kansas. In addition, 2.8 million acres of grain sorghum and 70,000 tons of residue were produced. While not all acres are suitable for grazing, this represents a tremendous resource for the state. Residue yield and nutrient contents are dependent on grain yield, fertility, harvest date, and conditions at harvest. The nutrient content of residues is additionally impacted by the duration and timing of grazing initiation.
The amount of grain left in the field has been reduced considerably compared to historical levels through varietal and harvest equipment improvements. However, weather conditions can result in significant ear drop or plant lodging. Before grazing, scout fields to look for piles of grain on the ground. If grain piles are found, steps should be taken to remove these piles before turning out cattle on the field. If there are a lot of downed heads or ears and over 8-10 bushels of estimated grain on the ground, caution should be taken before grazing to avoid acidosis. Directions to estimate grain on the field from ear and head drop can be found here. While sorghum grain is always processed prior to feeding to crack its tough shell coat, cattle can still founder on downed grain sorghum heads.
Nutritive value of corn and sorghum residues
A nutritional evaluation of grazed Kansas corn and sorghum crop residues was conducted with the help of numerous producers and county agents across the state. Table 1 summarizes values from that survey.
Table 1. Range of crude protein (CP), acid detergent fiber (ADF; higher values reflect lower digestibility), neutral detergent fiber (NDF; higher values reflect lower animal intake), and total digestible nutrients (TDN) in corn and sorghum residue from Kansas samples.
A more detailed look at plant components indicates that any grain available would have the highest CP content, followed by the leaves. The cob has the lowest protein and energy value. The stalk and husks have similar crude protein content, but more energy is available from the husks than the stalks due to the lower lignin content. In general, leaves from sorghum residue have higher CP content than corn leaves. The stalks of corn and sorghum are similar in CP, but digestibility is somewhat higher in sorghum than in corn. More details on nutrient concentrations of crop residues can be viewed in this UNL publication.
Nutrients in Residues
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