Grazing cattle on wheat in late winter/early spring always requires good management to maximize total returns from grain yield and cattle gains. There’s a fine line between getting more income from cattle grazing and leaving the cattle on wheat just a little too long so that grain yield is reduced.
Grazeout may be more profitable this year than removing the cattle and harvesting the wheat for grain, so be sure to take total potential return into consideration.
After greenup is underway and before the wheat has reached jointing, it is important to scout fields closely for signs of the “first hollow stem” (FHS) stage if you plan to harvest the wheat for grain. FHS occurs as the wheat switches from the vegetative stage to the reproductive stage of growth.
When the leaf sheaths become erect, the developing growing point, which is below the soil surface, will soon begin to form a tiny head. Although the head is quite small at this point, it has already established some important yield components. At this stage, the maximum potential number of spikelets is determined. Sufficient nitrogen (N) should already be available in the root zone at growth stage in order to affect the potential number of seeds per head.
Once the embryo head has developed, the first internode will begin to elongate pushing the head up through the leaf sheaths. This first internode will be hollow. This will be visible before you can actually feel the first node (joint, located just above the first internode). Prior to this stage the nodes are all formed but tightly packed together and hard to see.
FHS is the point at which a half-inch or so of hollow stem can first be identified above the root system and below the developing head. FHS occurs when the developing head is still below the soil surface, which means that producers have to dig plants out of the ground to do the examination.
To look for FHS, start by digging up some plants from fields that have not been grazed. Select the largest tillers to examine. Cut off the top of the plant, about an inch above the soil surface. Then slice the stem open from the crown area up. Look for the developing head, which will be very small. Next, see if you can find any hollow stem between the developing head and the crown area. If there is any separation between the growing point and crown, the wheat plant is at FHS. FHS will occur between a few days and a week or more prior to jointing, depending on temperatures.
Figure 1. First hollow stem occurs when hollow stem equivalent to the diameter of a dime (1.5 cm) is present below the developing grain head. Source: First Hollow Stem: A Critical Wheat Growth Stage for Dual-purpose Producers, Oklahoma State University publication PSS-2147, by Jeff Edwards, OSU Extension small grains specialist, and Gerald Horn, OSU beef cattle nutritionist.
If the wheat has reached FHS, cattle should be removed to prevent grain yield loss. Studies at Oklahoma State University have shown that grazing past first hollow stem decreases grain yield by as much as five percent per day or as little as one percent per day. Environmental conditions after cattle removal and the amount of green leaf area remaining on the wheat are among the factors that determine grain yield potential after grazing. Grain yield losses may be at the low end of this range for the first few days of grazing after FHS. Still, it is easy for producers to be late by a few days in removing livestock as they wait for obvious nodes and hollow stems to appear, and even the first few days can be significant.
Two things are observed when wheat is grazed too long: 1) fewer heads per acre because the primary tiller has been removed and 2) smaller and lighter heads than expected because leaf area has been removed. As cattle continue grazing, the wheat plant is stressed and begins to lose some of the tillers that would produce grain. A little later, if there is not enough photosynthate, the plant begins aborting the lower spikelets (flowers where seed develops) or some of the florets on each head. Finally, if there is not enough photosynthate during grain filling, the seed size will be reduced and if the stress is severe enough, some seed will abort.
Figure 2. Grazing past first hollow stem has been shown to reduce grain yield by as much as five percent per day or as little as one percent per day. Factors such as variety, grazing intensity and environmental conditions will determine the actual yield penalty for grazing past first hollow stem. This figure shows the anticipated yield loss for grazing past first hollow stem given favorable (solid line), unfavorable (dashed line) and average (dotted line) conditions for wheat regrowth following grazing termination. Source: First Hollow Stem: A Critical Wheat Growth Stage for Dual-purpose Producers, Oklahoma State University publication PSS-2147.
Jim Shroyer, Crop Production Specialist Emeritus