The amount of grain left in the field for cattle to eat after harvest has been reduced considerably in recent years through modern farming improvements. However, weather conditions can result in significant ear drop or plant lodging. Before turning cattle out for grazing, scout fields to look for piles of grain on the ground and determine if there is over 8-10 bushels of grain on the ground. If so, management should be taken to remove these piles prior to turning out cattle on the residue. Be sure that cattle have had access to plenty of hay before turning them out into cornfields, to keep hungry cows from gorging in grain.
Any grain available, in the field after harvest, would have the highest protein 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 milo sorghum residue have higher protein content than corn leaves. The stalks of corn and sorghum are similar in protein, but digestibility is somewhat higher in sorghum than corn.
To ensure adequate residue to protect soil remains on the field after grazing, we can use animal weight and grain yield to determine the amount of grazing available. Cattle will readily remove approximately 15% of the residue (leaves and husk), but can be forced to remove more if desired. The goal should be to leave at least ½ of the total amount of residue on the field.
If corn yield is 180 bu/acre, a rule of thumb is to divide by 3.5 to get grazing days for a 1200-pound cow. In this case, 180 bu/acre corn residue should provide approximately 51 days of grazing (180/3.5 = 51) for a 1200 lb cow. The harvest index is similar for both corn and grain sorghum, so an 85 bus/acre dryland sorghum divided by 3.5, would provide approximately 24 days of grazing (85/3.5 = 24). A lactating cow or a heavier cow will consume more dry matter and the days of grazing would be adjusted downward. And of course, a smaller animal could graze longer.
Cattle will selectively graze the crop residue, eating the highest quality portions first, grain then leaves and husks. Depending on the stocking rate, amount of grain available, and nutrient demands of the cows, no energy or protein supplementation may be needed early in the grazing period for dry cows with a body condition score of 5 or more. Contact your local extension office for more information about body Condition Scoring. Southwind Extension District Agent Christopher Petty is available for farm visits to explain this process using your cow herd. Weathering and trampling will decrease quality over time and this loss is greater with moisture and high humidity.
Cattle will cause soil compaction in paths leading to and around a water source. These compacted areas will only be surface compaction in the top 2-inches of soil. These compacted areas can be remedied by shallow tillage or spreading manure on the trafficked area if no-till is used. Results on soil compaction from grazing have shown mixed results. A study near Bushland, TX found surface compaction in a no-till system reduced crop yield after several years of grazing. While grazing studies from Nebraska found no increase in compaction and increased crop yield. Studies from western Kansas found compaction to only occur in the top two inches when grazing occurred on wet soils and shallow tillage removed any compaction. Compaction will be less on frozen, dry, sandy soils. It is best to remove cattle from the field to a nearby perennial pasture if the field stays wet and not frozen. Also, the farmer should be open to using light tillage should compaction occur.
Nutrient removal from grazing – Another common concern about grazing residue is nutrient removal. Nutrient removal will vary by the type of animal, with a growing calf requiring more nitrogen than a mature dry cow. Dry cows will typically be used to graze residue, which will remove between 1 and 2 lbs of nitrogen per acre (depending on crop yield) and few other nutrients. Crop residue is low in phosphorus; thus, farmers will likely supply a free-choice mineral, resulting in an increase in the amount of phosphorus and calcium left in the field.
When used properly, harvested corn and milo fields can work effectively to decrease the amount of hay needed to feed hay throughout the winter months. Unfortunately, soybean stubble is of little to no value, and cannot be used in the same manner. For more information about grazing grain stubble, contact your local extension office.