I have been spending the last few days in the field measuring forage production on ranches across my area. Estimating how much forage a pasture produces is important for those grazing livestock, because it directly correlates to how long a set number of livestock can utilize a given area. We typically estimate that one, 1000lb cow or her equivalent can consume 800 pounds of forage in one month. The table below outlines other animal unit equivalents that will also consume 800 pounds of forage in one month.
|Animal||Weight||AU Equivalent||# of Animals|
There are a few ways that one can measure or estimate forage production. When I am in the field and have time, I use the clip and weigh method. Other methods include ocular estimation, the use of Web Soil Survey, and for irrigated pastures the grazing stick.
To measure forage production using the clip and weigh method, which is what I was doing this last week, is fairly simple. You will need a few supplies. Those include a range hoop, gram scale, small paper lunch bag, clippers, and paper and pencil to record data. I use a 4.8 square foot range hoop, but there are other sizes available. I typically clip and weigh 3 plots or range hoops per pasture and average the numbers. You may want to do more depending on size of pasture, time, and plant communities found in the pasture. Now the fun begins! To randomly choose a plot, I swing the hoop over my head and let it sail out in front of me. Pretend you are throwing a lasso or a Frisbee. When the hoop has landed, I clip all forbs and grasses that are found in that plot to ground level. I put all the current year’s growth into a paper lunch bag labeled with the pasture, plot number, and date. I discard any old growth. I do not measure shrubs; however if you were grazing goats you might want to measure shrub growth. I repeat these steps two more times. The forage needs to be air-dried to give you an accurate reading. I let the paper bags sit for a few days, keeping them open to allow for air circulation. After forage has air-dried I then weigh the forage in grams. I can then take that number and multiply it by a conversion factor of 20 and this will get me pounds per acre. Each different hoop size will have a different conversion factor. For full instructions and more information on measuring forage production by the clip and weigh method check out this Utah Extension fact sheet.
Ocular estimation of range forage production involves training your eye to visualize how many Animal Unit Months (AUM) per acre can be found in the pasture. Remember that 800 lbs of forage is the amount of forage needed to feed one, 1,000 pound cow for one month. To visually estimate forage production first locate an area in the pasture that is representative of the amount of forage produced. Estimate the number of square feet it would require to feed that 1,000 lb cow for 1 day under moderate grazing intensity. You then multiply this number by 30.5 to get the number of square feet per month. Take that answer and divide by 43,560 which is the number of square feet in one acre. This will give you AUMs per acre. If you would like to convert this to pound per acre just multiply by 800.
Web Soil Survey is an on-line tool that allows users to access data collected by the USDA Natural Resources Conservation Service. Basically you use to tool to located a map of the pasture in question and based on data collected, you can locate the amount of forage that is expected to be produced if the site is in good condition in an above average, average, and below average precipitation year. Forage production data is based on collected data, plant species thought to be present, and soil type. This tool can give you a good baseline number of forage production for your operation. You can access that tool by clicking here: Web Soil Survey.
Using the grazing stick works well to estimate pounds of forage production on irrigated pastures. We know that there is a direct relationship between inches of forage height and pounds of standing dry matter. Although the relationship varies depending on species and stand density. Most grazing sticks will have tables that include this information. Take a walk through your pasture and measure the forage height in inches in several places to get a good idea of the average forage height. Always measure leaf height rather than seed head height. Use the tables on your grazing stick to convert inches to pounds per acre based on the type of grass and the value of the stand or its density. The following table is similar to what may be found on your grazing stick.
|Normal||Excellent (> 85% cover)|
|Pounds per acre per Inch|
|Cool Season & Legume||150-250||250-350|
|Cool Season Introduced||100-200||200-250|
|Cool Season Native||150-200||200-250|
|Native Mixed Cool & Warm||100-200||200-300|
|Warm Season Native||100-250||250-350|
If you do not have a grazing stick you can use a yard stick and this table to estimate forage production. Table was taken from the South Dakota State University Extension fact sheet: Using the ‘Grazing Stick” to Assess Pasture Forage. You can click on the link for more information.
Estimating or calculating forage production is an easy rangeland or pasture monitoring tool that can used to plan livestock grazing throughout the year. Forage production should be measured at peak standing forage, which will be determined by your location and the types of grass species present. For East Central Wyoming where I live and work, we typically measure peak standing forage in mid to late June as we have mostly cool season grasses. As we travel further east we tend to get more warm season grasses and measure peak standing forage may need to be done later in July. So get out in the field, enjoy the warm temperatures of summer, and have a great time measuring forage production.