Interactive Tools

How to Use This Calculator:

There are two sections to this calculator: The first is from using Table I below to determine your yield based on forage species composition and the expected pounds per acre-inch that your stand may be producing. The second is much more labour intensive, which involves collecting forage samples from your pastures, weighing them, drying them, then weighing them again to get an average dry matter yield value.

Using Table I

The values in the table below are the volume (pounds per acre) for every inch of grass or forage height.

Forage heights are taken using a yard stick and measuring the height of the forage stand as it naturally stands.

It is strongly advised to not stretch grass leaves up to their tips to get a height measurement, as that will lead to you calculating for more forage biomass than you actually have. This is true for both low-growing plants like Kentucky Bluegrass as well as upright grasses like Smooth Bromegrass.

How to Collect and Weigh Forage Samples

Using a 0.25-m² quadrat (this is simply a home-made 1″-diameter PVC pipe square that is 25-cm by 25-cm (9.84″ x 9.84″) in size, preferably as the inside measurements to maintain accuracy), take and collect 10 pasture samples by doing the following:

• Random sampling can be done by finding a spot and tossing the quadrat out, then sampling where it lands.
• Repeat by walking out several paces (1o to 20 steps) and tossing the quadrat again, until you have all needed samples
• BE SURE to not choose locations close to where you previously sampled. Mark these areas using posts with surveyor’s tape or marker flags so you know where you were last time.
• If the pasture is very large or contains different vegetative communities, or if it’s already divided up into paddocks, then you can do the following:
  • If hilly, be sure to sample at the mid-slope. Avoid sampling at the top or bottom, as this may skew the results;
  • Avoid sampling in thick brush or wooded areas where animals are most likely going to be loitering about as opposed to actively eating.
  • Try to avoid riparian or wetland zones especially if they are purposely being excluded from livestock for most of the year. An exception is ephemeral areas with lots of slough-bottom grass, which should be sampled separately from the rest of the pasture. (Too many of these samples can skew the results unfavourably against the rest of the lower-producing dryland areas.)
  • Take 2 to 3 samples per paddock, or in each different (non-woody) vegetative community.
  • Partition off different areas of the large pasture and sample in each area. Easiest is to partition by splitting it in half, thirds, or fourths. Take anywhere from 5 to 10 samples in each. (No issue if you want to limit samples to no more than 5 or 6 per area, as long as sample locations are very random and spread out from each other).
• Use paper bags to collect each sample; do not compile them all together in a single pail or one bag.
  • You could do this to make it easier, but it’s not recommended since the idea is to get a value from each quadrat you tossed and clipped from, and generate an average yield value from all.
• Clip (don’t pull) forage samples using hedge trimmer scissors, hand-scythe or similar leaving around 2 to 3 inches of stubble behind
• Stay within the quadrat itself, and collect everything, even the plants that your animals may choose to pick around. All contribute to the forage yield calculations.
  • If the stand is thick and tall with plants are falling in and around each other, do your best to move the plants whose stems are on the outside of the quadrat (or on the tool itself) aside with your arms so that you have the area you need to clip and collect from available. There is no need to clip other plants from around the quadrat. Just leave them where they stand and trample them down a little, enough to see where you can sit your quadrat down to ground level and begin clipping.
• Label each sample bag. When weighing and drying your samples, you will need to keep each bag until you are done weighing your samples.

Once you have your samples, it’s time to get their weights:

• Some other pasture management sources encourage you to pick out the dead material from the green, living plant material and taking the weight of the total forage weight and then the weight of the green plant material, and using the differences to determine your litter levels.
  • While this is very useful in seeing what the litter biomass is of your pasture and tells a lot about your management history, it’s also helpful to note that most animals are pretty indiscriminate when it comes to grazing, and will consume both dead and living plant material.
  • Thus, separating dead plant material from the living is an option, however it is a very time-consuming and tedious job, and should only be considered if you’re curious about what your plant litter yields are for your pasture. Skip this if you’re only concerned with overall forage yield.
    • If you’re wanting to do this, I highly recommend to pick out the dead plant material BEFORE drying it. Samples are more maleable and easier to work with when fresh than when they’re dry and stiff. Plus, it’s far easier to see which is dead material and which is still green living material than if you’re trying to pick out dead material after drying them!
    • Since this is an option, I’ve included it in the calculator below.
• Dry each sample using a food dehydrator or by leaving them out in a room to dry for 3 to 4 days (spread samples out evenly), or using a convection oven on a low setting (~300 degrees) for 20 to 30 minutes so that most of the moisture is taken out.
  • Weigh the dry samples in grams (g), and record each value. The calculator below will convert your average value into pounds per acre. (Note that 1 lb/acre is generally equivalent to 1 kg/hectare.)
  • Most kitchen scales are sensitive and decent enough to use to weigh your samples.
  • Make sure to tare the scale using an empty paper bag to zero, so that you are not including the weight of the paper bag along with the forage sample itself.
• Use the calculator below to enter your values and get the forage yield for your pasture.