Ministry of Agriculture, Food and Rural Affairs

Know the Amount of Feed in Your Pasture: A Dry Matter Yield Estimation Tool

What is a Falling Plate Meter?

A falling plate meter is a tool that can be used to estimate dry matter yield within grazing pastures (Rayburn and Lozier, 2003b). The falling plate meter is comprised of an acrylic plate and a meter stick. To estimate dry matter yield, the acrylic plate is lowered against a meter stick in the center of the plate onto the grass. At the point the plate is entirely held up by the grass, a bulk height measurement can be acquired on the meter stick (Figure 1). Often, in pasture management, a pasture height measurement is used to estimate dry matter. However, bulk height is a more accurate estimate of dry matter yield when compared to other nondestructive methods because a plate meter accounts for the density of the sward (Rayburn and Lozier, 2003a). Once a plate meter is calibrated, producers look up the average bulk height of their pasture on a chart which tells them the approximate yield.

Figure 1. Falling plate meter used to acquire bulk height measurement on pasture.

A falling plate meter can only be an effective tool in specific settings. This tool loses precision as grass matures; therefore, only yields of grass in a vegetative state can be estimated accurately (Castle, 1977). Like the structure of mature grass, yield of species with more woody stems such as alfalfa cannot accurately be estimated (Griggs and Stringer, 1988). Measuring pasture post-grazing depends on the state of the grass. If swards are trampled severely and no longer upright, a falling plate meter is not of much use (Li et al., 1998). For the same reason, it is not possible to accurately measure the yield of lodged grasses using this tool.

Current Research

Previous research on falling plate meters has focused on geographical locations with primarily one dominant grass species in pastures. In comparison, Ontario pastures have a vast biodiversity of grass species. This makes it difficult to relate studies previously conducted in other locations to Ontario's unique pastures. Therefore, a calibration of the falling plate meter must be completed specifically for pasture within Ontario.

To form the calibration curve, bulk height measurements and dry matter yields were taken for each sample. The dry matter yield was calculated using a tool called a quadrat which outlines the same area of grass the plate meter is being used on. In this case, the area of the quadrat is 0.092903m2 (12 in. by 12 in.) The grass is then clipped at 5cm above the ground, the minimum height at which ruminants should graze down to. The sample is weighed, dried and weighed again to determine the dry matter content. Yield is calculated and reported in kg/ha using the following equation: Yield (kg/ha)=((Dry weight (g)x0.001)x(10000/(Metric Quadrat Size))). Bulk height values on the x-axis are then graphed against yield on the y-axis to create a correlation between bulk height and dry matter yield (Figure 2).

After 12 weeks of sampling from May 14th, 2019 to August 7th, 2019, a preliminary calibration curve was developed, showing a relatively high correlation between bulk height and dry matter yield (Figure 2). The plan is to continue sampling over the next few years to build a statistically robust calibration curve across many different weather patterns over differing seasons.

Figure 2. Dry matter yield calibration curve based on samples taken from May - August 2019

Research Implications

This type of inexpensive, easy to construct, pasture measurement tool would allow Ontario farmers to take measurements of their own pastures with minimal training. The ability to accurately estimate yield on pastures would not only help put a value on pastures but will also help producers implement best management practices to optimize performance of cattle on pasture.

References

Castle, M. E. (1976). A simple disc instrument for estimating herbage yield. Grass and Forage Science,31(1): 37-40.Griggs, T. C., & Stringer, W. C. 1988. Prediction of Alfalfa Herbage Mass Using Sward Height, Ground Cover, and Disk Technique. Agronomy Journal,80(2): 204.

Li, G. D., Helyar, K. R., Castleman, L. J., Norton, G., & Fisher, R. P. 1998. The implementation and limitations of using a falling plate meter to estimate pasture yield. The Regional Institute,322-325.

Rayburn, E., & Lozier, J. 2003a. Estimating Pasture Forage Mass from Pasture Height. West Virginia University Extension Service.

Rayburn, E., & Lozier, J. 2003b. A Falling Plate Meter for Estimating Pasture Forage Mass. West Virginia University Extension Service.