Using The ‘Grazing Stick’ To Assess Pasture Forage

By Pete Bauman

Assessing pasture forage is a key step in planning grazing strategies. Although most producers understand the importance of assessing production, few invest the time necessary to clip and weigh vegetation within and across seasons in order to build a long-term database for their pastures. Recognizing this inherent need, range managers have developed simplified tools that allow rapid estimation of forage production and availability in pastures without the need to continuously clip and weigh vegetation. One of these tools is the common ‘grazing stick’.

While all grazing sticks are based on the same general principals, their use can be modified to fit local conditions. Here we introduce the grazing stick developed for the South Dakota Grassland Coalition by the South Dakota Natural Resources Conservation Service. This stick is distributed at multiple grazing management events throughout South Dakota. While small modifications have been made over the years, any version of the South Dakota grazing stick will adequately serve to help estimate your pasture conditions.
How does the grazing stick work?

The grazing stick utilizes simple plant leaf height measurements in inches. For every inch of growth, the grazing stick estimates how many pounds of dry plant material are available. This number is then represented as lbs. per acre per inch of growth. So, 10 inches of growth at 100 lbs. per inch equates to 1,000 lbs. per acre of dry plant material. The grazing stick includes simple math to determine herd size, stocking rates, and available grazing days. We will address how to use the grazing stick in steps.
Step 1: Timing

When to assess pasture forage is a common question. In South Dakota, the growth and development of our pastures is largely dependent on the dominant plant community such as: 1) native cool season grasses (native wheatgrasses, needlegrasses), 2) non-native or invasive cool season grasses (Kentucky bluegrass, bromegrasses, exotic wheatgrasses), 3) native warm season midgrasses (blue grama, buffalograss), 4) native warm season tallgrasses (big bluestem, indiangrass, sideoats grama), or 5) a mixture of grasses and forbs from several of these categories. To assess total production for pastures dominated by cool season vegetation, late June to early July approach peak production. For a warm season dominated pasture, mid-to late August works well. However, pasture production can be assessed at any time to determine stocking rates or grazing days within a rotational grazing system and should be measured prior to moving livestock to the next pasture in the rotation.
Step 2: How and where to measure

The grazing stick is designed to measure the average leaf height of the vegetation in the pasture by providing a simple yard-stick style ruler on one side. The first part of the stick to notice is the DO NOT GRAZE indicator that reminds a producer not to remove the vegetation beyond a height of 4 inches. Generally ½ of a plant’s above ground biomass is located in the bottom 1/3 of the plant. Removal of over 50% of a plant’s biomass can severely impact root development, requiring long-term rest for the plant to recover. The 4 inch mark is provided as a safety measure for producers and should not be ignored (figure 1).

Figure 1. DO NOT GRAZE indicator. Pasture is clearly grazed beyond the recommended height.

For the grazing stick to accurately determine overall forage availability, leaf height must be measured in an upright position. Trampled vegetation may need to be held upright in one hand in order to determine the average leaf height of the grass, not total plant height. Therefore stems and seed heads of tall grasses should not be used when measuring average leaf height (figure 2).

Figure 2. Trampled vegetation must be held upright for an accurate measurement of leaf height. Tall stems and seed heads are not included in estimating the overall leaf height.

Using The ‘Grazing Stick’ To Assess Pasture Forage


A good rule of thumb is that grazing stick measurements should be taken at no less than 15 to 20 locations within a pasture. Areas where measures are taken should be a fair representation of the overall pasture vegetation. Distribution of various types of vegetation should be considered as well. For instance, in a 100-acre pasture that is dominated by warm season grasses on the west side and cool season grasses on the east side, a good strategy may be to take 15 measurements on each side and work through the grazing stick methodology, averaging the final production numbers together.

For a pasture with equal distribution of a variety of vegetation, one must decide which vegetation category of the grazing stick most closely fits the situation. Vegetation categories are found in the ‘Estimated Air-dry Weight’ table on the stick. This table includes information on the plant community. The user must choose which plant community and stand density most closely represents the pasture conditions (figure 3). To determine stand density, one must look ‘into’ the stand to determine relative density. This is where the grazing stick table in figure 3 assists the producer. Notice the notes on the bottom of figure 3 indicating stand density should be greater than 85% to qualify as excellent.

Figure 3. Determining plant community, stand density, and production.

Vegetation cover can be somewhat subjective. The grazing stick table allows for a great deal of flexibility in determining the range of lbs. per inch of production within the stand density table (figure 3). It is up to the producer to decide how many lbs. per inch are likely being produced within the chosen stand density category. Also, within a given plant community in a single pasture, the stand density can be variable depending on the landscape, slope, soils, and other conditions. The producer should evaluate the lbs. per inch at every measurement if there is a high variability in stand density. The best way to accurately determine lbs. per acre is to calibrate your grazing stick estimates via a true forage clipping estimation.

As an example, figures 4 and 5 below are provided to help the user understand the nuances of stand density estimation. Figure 4 depicts a mid-July pasture dominated by smooth bromegrass, which is a ‘cool season introduced’ plant community in the grazing stick table. This stand would likely be categorized in the ‘Normal’ range, producing an estimated 100 lbs. per inch based on its fairly low density and relatively short (20 inches) stand height. Figure 5 depicts a mid-July pasture dominated by big bluestem, which is a ‘warm season native’ plant community in the grazing stick table. This stand would likely be categorized in the ‘Excellent’ range, producing an estimated 300 lbs. per inch based on its high density and relatively tall (34 inches) stand height.

Figure 4. Low density and fairly short smooth bromegrass stand

Figure 5. High density big bluestem stand.

Step 3: Estimating average lbs. per acre production

Once several height measurements have been taken and a general stand density estimate has been determined by averaging samples across the pasture, simply multiplying the average height from the measurements by the average lbs. per inch will yield the average lbs. per acre value for the pasture. An average of 20 inches of growth with an estimated 100 lbs. per inch in our smooth bromegrass stand in figure 4 would yield about 2,000 lbs. per acre. At 34 inches of growth with an estimated 300 lbs. per inch, our big bluestem stand in figure 5 would yield over 10,000 lbs. per acre. It is important to understand that at this point we’ve only estimated our potential yield. This number does not equate our forage supply (available forage).

Step 4: Determining forage supply (grazing efficiency) and forage demand

Forage supply is an estimate of how much available forage is in the pasture. It is determined by multiplying the forage production by the percent of the forage the manager is willing to remove through grazing. The basic rule of thumb is the standard ‘take ½, leave ½’ approach. The basics of this approach calls for 50% of the forage to remain in the pasture as ungrazed, while 25% is consumed by livestock and 25% assigned to disturbance through trampling, defecation, and consumption by other grazers such as insects, and small mammals. In this scenario, our smooth bromegrass pasture would have a forage supply of 500 lbs. available to be grazed (25% of 2,000 lbs.) while our big bluestem pasture would offer over 2,500 lbs. of available forage. As one increases the number of pastures in a grazing rotation, the allowances for grazing efficiency also increases. Figure 6 highlights the grazing rotation chart offered on the grazing stick to help producers determine the forage supply (grazing efficiency) of their pastures.

Figure 6. Rotation and grazing efficiency chart

Forage demand is determined by the type and size of livestock and the conditions under which they are grazed. The simple chart provided on the grazing stick can help the producer determine an estimate of daily or monthly forage intake of the herd. For general purposes, a standard measure for a lactating beef cow is about 3% of body weight, or 30 lbs. of dry matter per day for a 1,000 lbs. cow. Heavier cows will consume more total pounds at the same 3% intake rate. The grazing stick again offers a simple chart to assist producers in these estimates (figure 7).

Figure 7. Average forage intake chart

Step 5: Calculating grazing days, herd size, or acreage needed.

Once the forage supply and the daily forage demand has been calculated, one can use the numbers to determine: 1) the size of pasture needed to graze a certain number of animals 2) the number of animals a given pasture can carry during a pre-determined timeframe, or 3) the number of available grazing days a herd may have in a particular pasture. These simply calculations are provided on the grazing stick in figures 8 and 9 below.

Figure 8. Calculating forage supply, forage demand, and pasture size with the grazing stick

Forage Supply
lbs./acre (air-dry) X %Grazing Efficiency = lbs./acre forage available
(%Grazing Efficiency = 25% - 1 pasture; 35% - 4-8 pastures;
40% - 12+ pasture MIG)

Forage Demand
Animal Weight X 3.0% of Body Weight = lbs. forage required/day
(Or use Average Forage Intake Table)

Figure 9. Calculating animal number and grazing days with the grazing stick.

Animal
Number