Seven Steps for Conducting a Forage Survey
1. Determine grazable acres per range site and pasture. Using a recent aerial photograph and soil survey information, draw the pasture and range site boundaries and non-grazable areas, such as lakes, roads, homestead, inaccessible terrain and unproductive areas. It may be necessary to inspect each range site to estimate unproductive acreage including brush motts or thickets not observable on the aerial photograph. Determine total acres for each range site; then calculate grazable acreage by subtracting non-grazable acreage.
2. Locate representative areas in each range site. Representative areas in each range site will be sampled to determine the forage supply. These areas should be representative of the average grazing use for the range site. Do not sample adjacent to bed grounds, water points, mineral/feeding locations, or areas that are seldom grazed.
3. Select appropriate plot size that matches the type of vegetation to be sampled (Table 1). Construct the plot frame using 3/8" reinforcement rod (welded) with inside dimensions as shown in Table 1.
| Vegetation Type | Plot Dimensions | Conversion Factor* | |
|---|---|---|---|
| grams | ounces | ||
| Arid, less than 15" rainfall | 39.4" x 39.4" | 8.92 | 25.29 |
| Semi-arid, 16 to 30" rainfall | 27.8" x 27.8" | 17.84 | 50.59 |
| Humid, 31" or more rainfall | 19.7" x 19.7" | 35.64 | 101.05 |
| * Measure harvested oven-dry sample weight (less sack weight) in grams or ounces and multiply by the conversion | |||
4. Develop a representative photoguide. A photographic reference of known forage quantities for the various range sites on your ranch is used to improve estimation consistency between samples. The photoguide represents the variation of forage supply conditions that will be observed in the pastures. Approximately 10 photographs of known forage quantities arranged from the lowest to the highest quantity should be used (Figure 1). In the representative range site areas, select plot locations that show different quantities and species mixtures. Place the plot frame over the vegetation to be photographed. The frame perimeter should be clearly visible in the photograph (i.e. PVC pipe was used in the example photoguide). Only vegetation rooted in the plot should be sampled; therefore, separate vegetation into or out of the plot frame. Each photograph should indicate height, density and cover of vegetation. High contrast black and white photographs are recommended. [Next Page]
Authors: Larry D. White, Calvin Richardson