Using the ‘Grazing Stick’ to Assess Pasture Forage Back »

Assessing pasture forage is a key step in planning grazing strategies, especially if one is utilizing grazing as a tool toward wildlife habitat or other grassland conservation objectives. Although most producers understand the importance of assessing production for livestock gain, 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. In addition, conservation landowners may not feel they have the ‘knowledge’ to challenge grazing contractors on what they may perceive as undesirable pasture management. 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 principles, their use can be modified to fit local conditions or objectives. Here we introduce the grazing stick developed by the South Dakota Natural Resources Conservation Service for the South Dakota Grassland Coalition. 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 and grassland 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. of dry plant material per acre. 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. Ultimately, the grazing stick can be a valuable tool for landowners who wish to utilize grazing as a management tool while retaining a measurable amount of habitat on their property.

Step 1: Timing

When to assess grassland production is a common question. In South Dakota, the growth and development of our grasslands 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 grasslands dominated by cool season vegetation, late June to early July approach peak production. For a warm season dominated grassland, mid-to late August works well. However, grass 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 grassland 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. This is a minimum to protect the plant and may or may not equate to wildlife objectives. 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 all 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.
 

A good rule of thumb is that grazing stick measurements should be taken at no less than 15 to 20 locations within a grassland area. Areas where measures are taken should be a fair representation of the overall grassland vegetation. Distribution of various types of vegetation should be considered as well. For instance, in a 100-acre area 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 grassland 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 it is necessary to look down ‘into’ the stand from above to get a feel for how much area is covered by vegetation (see figures 4 and 5). This is where the grazing stick table in figure 3 assists the producer. Notice the notes on the bottom of figure 3 indicating that to qualify as excellent stand density should be greater than 85%.

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

Estimated Air-dry Weight in pounds per inch* Minimum
Stubble
 
Stand Density**
Plant Community Normal Excellent Height
Cool Season & Legume 150 - 250 250 - 350 4"
Cool Season Introduced 100 - 200 200 - 250 4"
Cool Season Native 150 - 200 200 - 250 4"
Native Mixed Cool & Warm 100 - 200 200 - 300 4" to 6"
Warm Season Native 100 - 250 250 - 350 6" to 8"
*Measures the average height in inches of the vegetative forage in the plant community, not seed head height.
**Stand density refers to the relative closeness of desirable plants. An excellent stand density will have a cover greater than 85% and be vigorous.

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 production in lbs. per acre

Take several height measurements and determine a general stand density estimate by averaging samples across the pasture. Then simply multiply the average height from the measurements by the average lbs. per inch to obtain the average lbs. per acre value for the pasture. An average of 20 inches of growth with an estimated 100 lbs. per inch in the 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, the big bluestem stand in figure 5 would yield over 10,000 lbs. per acre. It is important to understand that at this point only the potential yield is estimated. This number does not equate 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, the smooth bromegrass pasture would have a forage supply of 500 lbs. available to be grazed (25% of 2,000 lbs.) while the 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.

For wildlife habitat purposes, landowners may want to restrict grass consumption and overall impacts to much less than 50% at certain times during the growing season. Also, landowners may choose to allow heavier utilization in portions of the pasture to create a ‘mosaic’ of habitats suitable to nesting, chick foraging, and escape cover.

Figure 6. Rotation and grazing efficiency chart

Rotation (180-Day Grazing Period)
No. of Pastures Grazing Efficiency Grazing Days Rest Days
1 25% 180 0
2 30% 90 90
3 30% 60 120
4 35% 45 135
6 35% 30 150
8 35% 23 157
12 40% 15 165
16 40% 11 169
 

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

Average Forage Intake (Air-dry basis)
Species Animal Weight x % Intake =
Forage
(lbs. per Day)
Forage
(lbs. Per Month)
Sheep 130 x .037 = 4.8 146
Sheep 200 x .037 = 7.4 225
Yearling 650 x .03 = 19.5 593
Yearling 850 x .03 = 25.5 775
Cow 1000 x .03 = 30 912
Cow 1200 x .03 = 36 1094
Cow 1400 x .03 = 42 1277
Cow 1600 x .03 = 48 1459

 

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

Once the forage supply and the daily forage demand have 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 simple 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)
Pasture
Size (Ac.)
Forage Demand (lbs./day) X #Animals
Forage Supply (lbs./acre)
X Grazing Period
in Days
 

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

Animal
Number
Forage Supply (lbs./acre)  X  Pasture Size in Acres
Forage Demand (lbs./day) X Grazing Period (days)
Grazing
Period (Days)
Forage Supply (lbs./acre) X Pasture Size in Acres
Forage Demand (lbs./day) X # of Animals
 
Avoid grazing the same native pasture at the same time every year.
Slow plant growth - move slow Fast plant growth - move fast
Rest, rain and leaf area grow grass Take half, leave half by weight
Bottom 1/3 of plant height equals approximately 1/2 of plant weight
 

Scenario 1 – calculating pasture size (figure 8):
In some cases, there may be a need to graze a fixed number of animals for a fixed period of time, and the producer must determine how many acres are necessary. Step one is to determine forage demand. If we have 1,500 lbs. cows, we can determine the daily forage demand per cow (1,500 lbs. x 3% = 45 lbs. of dry matter per cow per day). A single cow will need 6,750 lbs. of forage dry matter for a 150 day grazing period (45 lbs. per day X 150 days). A herd of 100 such cows will need 675,000 lbs. of forage dry matter for the season. If these cows are to graze on only one pasture for the season, we would then assign a grazing efficiency of 25%.  To determine the total forage production necessary to sustain the herd, we can now divide 675,000 lbs. by 0.25, which equates to 2,700,000 lbs. of forage production necessary. To figure our acres needed, we then divide the 2,700,000 total lbs. needed by 2,000 lbs. per acre production in our brome pasture, yielding an answer of 1,350 acres necessary to sustain this herd for the 150 day season.

Scenario 2 – calculating herd size:
If we know we have a certain amount of forage available and we want to ensure grazing for a certain number of days, we can also calculate our animal number using the grazing stick. If we use the single 100-acre brome pasture at 2,000 lbs. per acre production and 25% harvest efficiency, we will have 50,000 lbs. of available forage. If we want to utilize that pasture for 150 days and we have the same 1,500 lbs. cows, we know from scenario 1 above each cow will need 6,750 lbs. of forage through the season. To determine the number of cows we can graze, simply divide the available forage (50,000 lbs.) by the lbs. per head for the season (6,750 lbs.). Therefore, we can graze about 7.4 cows on this pasture for the season.

Scenario 3 – calculating grazing days:
If we have a similar herd of twenty 1,500 lbs. beef cows, we know they need 900 lbs. of forage per day (20 cows X 45 lbs. per day per cow). We know from scenario 2 above that the forage supply is 50,000 lbs. At 50,000 lbs. available forage, the pasture can handle our herd of twenty cows for about 55 days (50,000 lbs. / 900 lbs. per day).

Of course, it is always necessary to account for forage quality and timing of grazing, but if used properly the grazing stick can help a producer become more familiar with his or her grasslands and their ability to provide habitat at critical times of year, gaining valuable insight over time in order to assess grazing potential and the nuances that might impact the pastures and the ranch as a whole.

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