written by Karen Colson and Jason Karl
Description and Uses
The Actual Weight Method is an individual-plant based technique where utilization is estimated by comparing the average weight of grazed plants to ungrazed plants. It involves separately clipping and weighing current year’s growth from a series of grazed plants located along the transect and a series of ungrazed plants along the transect. These plants are then weighed. The difference between the weights of the grazed and ungrazed plants represents the amount of forage consumed by animals or otherwise destroyed during the period of use. In cases where not enough ungrazed plants can be located, cages or similar reference areas must be used to obtain the ungrazed weight.
This method was developed for use on clearly defined growth forms such as bunchgrasses. It is not recommended in areas where the key species are shrubs or rhizomatous plants. However, it can be used on sodforming grasses if a small quadrat, 2 or 3 inches square, is used to delineate a unit. This method is best adapted to short duration grazing on small pastures, which reduces the effects of regrowth.
Advantages and Limitations
The Actual Weight Method is simple and direct way to measure utilization. It is also accurate and compared to other methods which estimate utilization, this method reduces personal error because actual weight measurements are taken. In addition, little training is required for accurate measures of utilization.
The main limitation is that this method is very time consuming. It is restricted to a small set of plants, primarily bunchgrasses and sod-forming grasses. In addition, when ungrazed plants are not available, cages or similar reference areas in ungrazed pastures are required to obtain an estimate of the ungrazed weight.
Similar to all harvesting techniques, this method is destructive because plots are clipped and new plots must be located after each sampling period.
Utilization Studies and Residual Measurements (Technical Reference 1734-3) http://www.blm.gov/nstc/library/pdf/utilstudies.pdf
Related utilization and residue measurement methods include: