Forage Information System

Good pasture condition is foundational to developing a successful grazing system. Pasture condition is "the status of the plant community and the soil in a pasture in relation to its highest possible condition under ideal management." Components of pasture condition include species composition, land cover, yield, and quality (including palatability and digestibility). Once these components are assessed, informed decisions can be made about the need for renovation or re-seeding.

Assessing pasture species composition

Pastures are typically complex mixtures of many species, some being more desirable than others. An important aim of management is to optimise the composition of those mixtures to improve productivity and sustainability of the pasture. This requires ability to determine what species are present, which ones are desirable, which ones are less desirable or harmful, and how to manage for the species you desire. 

Assessing pasture productivity (yield and quality)

Assessing the current level of pasture productivity is important in deciding whether to expend resources for renovation or re-seeding of pastures. Several methods can be used including simple height measurements, cutting and weighing, pasture sticks, or rising plate meters.

Pasture Height. Since forage mass increases as plants get taller, measuring   pasture height is a method often used for making quick yield estimates (Figure   1).

One estimate that has frequently been used to relate pasture height to its mass is 200 pounds of dry matter per inch of height (Barnhart, 1998). Table 1 was developed for pastures in southern Iowa and northern Missouri.

Table 1. Estimated dry matter yield in pounds per acre per inch of height for pasture types and stand conditions (Iowa State University).

Table 2 was developed jointly by Cornell University and the NRCS.

Table 2. Estimated dry matter yield in pounds per acre per inch of height for pasture types and stand conditions (University of Maine Cooperative Extension Pasture Management Online Course).

Pasture SpeciesStand ConditionFairGoodExcellentBluegrass/Clover150-200*250-300350-400Perennial Ryegrass/Clover150-200250-300350-400Orchardgrass/Legume150-200250-300300-350Timothy/Legume150-200250-300300-350Tall Fescue + Nitrogen100-150200-250350-400Mixed Pasture150-200250-300300-350

*Pounds/acre/inch values from Pasture Stick developed by Cornell University and NRCS

Other estimates that have been used in New Zealand for more dense pastures (e.g. perennial ryegrass and white clover) are 1,000 pounds of dry matter in the first inch (from the soil surface) and 500 pounds DM/inch in subsequent inches.

Whatever multiplier you are comfortable using, determine the average vertical height of the undisturbed stand of forage species in inches, and multiply the height by the estimated pounds/inch estimate to predict the amount of forage mass on offer. (Estimating the amount available for removal by grazing or mechanical harvest must subtract the amount remaining after defoliation.)

Clipping and Weighing. Actually measuring the dry matter in the pasture is the most accurate way to estimate pasture productivity (Barnhart, 1998). To do this, you must cut the forage from several areas in the pasture representing the variation in the vegetation found there.

Use a hoop (or square or rectangular quadrate) to calculate how many square feet you are clipping; throw the hoop at random, then clip the standing forage inside the ring down to the ground (Downing, 2001). Figure 2 shows a hoop that measures 1 square foot. Cut at least 10 to 15 sample plots per field, depending on the size of the field and the variation in the height of existing forage. The larger the field, or the greater the variation in forage height, the more samples you need. The more uniform your forage height, the more accurate your estimate.

By calculating the total square feet clipped and weighing the forage, you can determine how many pounds of total feed were standing per acre before grazing. An acre is 43,560 sq ft. Divide your total clipped area into 43,560; then multiply the answer times the weight of the forage clipped to determine your estimated pounds of standing wet grass per acre. Measuring again after grazing tells you how much forage was removed.

To determine pounds of dry matter (DM) per acre, however, you need to know what percentage of the forage is dry matter versus moisture. A commercial forage lab can analyze the forage, but the following process lets you perform a quick moisture test at home with a small scale and a microwave oven.

1. Weigh a paper bag large enough to hold 4 ounces of the clipped forage. Write down the weight as value A.
2. Place about 4 ounces, or 100 grams, of your forage into the bag and weigh again. This becomes value B.
3. Place a cup of water in the corner of the microwave oven and the filled bag in the center. Dry the sample at a medium power setting for 3 minutes. Remove the sample and stir gently, then dry for another 1 1/2 minutes. Stir again, then dry for another minute.
4. The sample should be getting dry and crisp. Weigh the sample and bag, stir again gently, then dry for another 30 seconds. Continue 30-second drying and weighing intervals until the weight measurement reads the same twice. Record the final weight as value C. If the sample begins to char, use the previous measurement.
5. Calculate the dry matter content using this formula:

%DM=Total dry weight "C" bag weight "A" x 100
Total wet weight "B" bag weight "A"

Grazing Stick

The manual version is a three foot long stick marked with different species of forage that you can estimate the forage density. [Purdue link]

The electronic version is called a capacitance meter (Figure 3). It is an electronic device that uses radio frequencies to make electrical measurements of forage density, storing the measurements and calculating estimates of dry matter in standing forage as you walk across the field. Take a least 30 to 40 measurements to get a good estimate of the variability in the pasture.

Rising Plate Meter. (Manual or Electronic):

Another common method of measuring forage in the field involves a rising plate meter (Figure 4). This device estimates standing forage dry matter by accounting for pasture height and density. The electronic meter pictured allows the operator to select the cover equations that most closely represent existing pasture conditions. To determine the correct cover equation, take 30 to 50 pasture clipping samples per paddock to establish an average reading. Once calibrated, the device will provide standing forage measurements in pounds of dry matter per acre or kilograms per hectare. Most commercially available rising plate meters are made in New

(Source: Downing, 2001)

Renovation / re-seeding decision making

Evaluation of the stand is the first step to renovation. Stand evaluation will give you an idea of whether you have enough desirable forages left to attempt improvement. (See the previous subsections in this section for more details on stand evaluation.)

Renovation through partial or complete tillage, chemical weed control and suppression of existing vegetation, fertilization and liming, and reseeding is expensive and typically thought of as the last choice in pasture improvement. Changes in grazing management and improvement in fertility are typically the first recommendation to improve forage production. This is because results will not change until the land manager develops a different philosophy about grazing land management and puts that philosophy into action with different practices.

The following concepts apply to all sites being considered for renovation.

• First, evaluate the current management of the site. If you’re ready to reseed, then you must not like what is growing on the site. However, what is growing there now is what is best adapted to how the site is currently being managed. If the area is reseeded, but the management is not changed, the site will soon return to its present condition. [Management changes might include more cross-fencing to allow more intensive rotational management, moving current fences so that different soil types are not fenced together into one unit, or creating a winter confinement area to protect pastures when soils are saturated and the grass isn’t growing very fast.]
• “Plant only fence posts for the first three years after a change in grazing management.” (Ron Morrow, Natural Resources Conservation Service (NRCS) State Grazing Lands Specialist from Little Rock, Arkansas.) Under good grazing management it takes about three years for a pasture to improve in yield potential and to know its botanical composition of plant species.
• Don’t renovate more than 20% of the fields or acres in one year. Pasture or hayland forage will still be needed before the new seedings are ready to be used. Summer drought or winter flooding weather may damage or kill the new seeding before the plants have become established.
• Evaluate the current soil status with a soil test. Contact your local Cooperative Extension, Natural Resources Conservation Service, or Conservation District office for information on how to take a soil test and where to have it analyzed. Does the soil need lime? Prior to forage renovation is an excellent time to apply lime or other elements.

(Source: Fransen and Chaney, 2002).