Topics : Pastures : Determining Pasture Yield
Determining Pasture Yield
Additional pasture information via the Forage Information System (FIS)
Hand Clipping: This method involves clipping, drying, and weighing samples. The precision of this method largely depends on pasture variability and sampling efficiency. Hand clipping is precise but time consuming which makes it impractical on a routine basis.
There are a large number of indirect methods that have been developed to estimate yield. Among them the pasture ruler and the rising plate meter are the most used. Both methods need to be calibrated to the specific situations. There are general equations, but if precision is important either method needs to be calibrated. Calibration procedures are similar for both methods and are explained here.
Pasture ruler: This method works on the principle of relating the plant height to yield. Therefore we need to calculate the average pasture height. This is accomplished by walking through the paddock in a W pattern and recording the plant height at a 25-footstep interval. It is important to take the measurement at the same space interval regardless of the spot. The height of both bare spots and dense (manure effect) spots must be recorded. Avoiding spots will lead to a biased average height value and yield will be miscalculated. Once the height data is collected simply average the height (sum of all heights recorded divided by the number of samples). In Pennsylvania, DM accumulation averages about 300 lb per inch of plant height. To convert the average plant height to yield, simply multiply it by 300 lb DM/inch. The pasture ruler method is fast, simple, and cheap. Unfortunately it is less precise than the hand clipping. Click here for an example of the pasture ruler method, or click here to perform the calculation.
Rising plate meter: This method relies on both plant height and density. These two characteristics are combined into one measurement, often referred to as “bulk density”. To estimate yield with the rising plate meter a similar procedure is followed as with the pasture ruler. Before data collection the sample counter should be set to zero and the initial rising plate value recorded on the accumulative pasture meter. Then a W pattern in the pasture is followed to estimate the average plate meter. At a fixed pace interval (25 footsteps) the pasture meter is pushed vertically into the sward and at the same time the sample counter is clicked once. The rising plate reading must be taken at the set pace interval to avoid bias in the plate meter estimation. This operation is repeated at each sampling point. At least 20 rising plate readings must be collected regardless of the paddock size. When finished collecting the rising plate values, the final plate number is recorded. The average plate meter is calculated by subtracting the initial value from the final value and dividing by the number on the sample counter (which equals to the number of times the plate meter was pushed into the sward). This average plate meter is correlated with forage bulk density. The average plate meter reading is then converted to yield using a calibration equation. The rising plate meter method is more precise than the pasture ruler, but needs a greater investment both in time and money. Rising plate meter yield determination example. Click here to perform the calculation.
The equations used for the yield calculation were calibrated to be robust enough to adjust to most situations encountered in Pennsylvania pastures. However, to increase precision both the pasture ruler and the rising plate meter should be calibrated to the particular situation in which they are intended to be used. The rising plate meter will underestimate yield in pastures covered by heavy dew, in pastures in flowering stage, and in extremely tall pastures (over 14 inches tall). Accurate DM determination will aide in the decision-making process of pasture management.