Accurately estimating standing crop production of forages is critical in determining carrying capacity and/or reserve herd days in a pasture. There are several ways to estimate forage production, ranging from direct sampling (i.e., clipping plots) to ocular estimates. Despite the importance of accurately estimating forage production, most people are not willing to spend the time clipping and weighing samples to increase the accuracy of their estimates. We suggest an exercise of determining the average height of the forage with a ruler, yard stick or "grazing stick" and making an assessment of the density of the stand. This information, compared to the pictures in the pictorial yield guide, should help producers make a more accurate assessment of forage quantity in their pastures. The following photos depict bermudagrass and annual ryegrass with different heights and densities along with the actual production values (pounds/acre) for these plots. These examples should help producers "calibrate their eyes" and/or give them a reference for a known quantity of forage per acre to compare to their specific situations to more accurately determine forage production. The plot is constructed of a 50 cm. x 50 cm. square frame made out of PVC pipe. Each plot was photographed twice; once looking across the plot (horizontally) with a ruler in the background to determine stand height and once looking directly down on the plot (vertically) to determine stand density. After taking the pictures, current year's growth was clipped at ground surface, bagged, oven-dried and then weighed. Pounds per acre of dry matter was then calculated.
The main value of a pictorial yield guide is that it allows you to compare the density of the forage in the picture with that in your pasture. We will often use an average of 250 lbs. of bermudagrass forage per acre-inch as a conservative planning number when estimating forage production, however the bermudagrass plots in these photos range from 350 to 445 lbs. of forage per acre inch. Without the pictures to compare, we could have under-stocked by 40 to 78 percent.
Here's another example of how this guide could be used. Say you had four 15-acre bermudagrass pastures, 20 head of 1,200 lb. beef cows and it is the middle of July. Two of the pastures very closely resemble the pair of pictures depicting bermudagrass averaging 6 inches tall, moderate density and 2,100 lbs. of forage per acre. These cows would require about 30 lbs. of forage per head or 600 lbs. per day for the entire 20 head. We can usually count on 40 to 60 days of very dry weather beginning in July in the Southern Plains. So even if it didn't rain for that amount of time, these two pastures should last about 65-70 days or until the first week of October, grazing to a minimum 2-inch stubble height. This would give you the choice to either allow for needed grass recovery or hay the remaining two pastures.
Producers need quick and easy tools to help them determine the productivity of their pastures with reasonable accuracy. This article contains examples of pictorial yield guides that are currently being developed at the Noble Research Institute for use in southern Oklahoma and northern Texas. These pictures should provide a reference for a producer to better estimate forage production in a pasture. Initial clipping and weighing may be necessary to account for site-specific conditions.
Rob Self of the Nature Conservancy, Brown Ranch Preserve, Milnor, ND, contributed to this article.