written by Karen Colson and Jason Karl
Description and Uses
Plant production can be determined using a variety of methods or combination of methods including estimating, harvesting, or by estimating and harvesting (double-sampling). Although the harvesting method is highly accurate, it is also very time and labor intensive. In contrast the estimation method is more rapid but not as accurate. By combining the harvest and estimation methods, the Double-Sampling Method can reduce the time it takes to sample and is still fairly accurate. This procedure basically requires that the observer estimate the weight of several plots and then clip a few more plots to determine the accuracy of the estimates. Based on this information, adjustments to the estimated weights can be made if necessary.
Advantages and Limitations
The Double-Sampling Method is less time consuming than the harvest method (since estimating is faster than clipping) and is more accurate than the estimation method (since estimating production can be subjective and cause error). However, it still requires a lot of training, which involves weighing representative units of a plant and training the observer to be able to see what the weight categories look like.
Similar to the other two methods, plants grow at different times of the year so when the sampling is conducted is important since sampling at different times of the year can change the results. When measuring annual production, current year’s growth can be hard to separate from previous year’s growth. Likewise, seasonal and annual climatic fluctuations affect biomass, and therefore production is not a suitable measure for long-term trend studies that compare data taken in different years. It also requires adjusting for material that has not been produced yet or has been removed which is difficult.
This methods still requires disturbing some of the vegetation on the site but not as much as the harvesting method.
- NRCS National Range and Pasture Handbook, Chapter 4, Inventory and Monitoring Grazing Land Resources, pages 4-3 through 4-13 (USDA-NRCS 1997).
<flashplayer width=600 Height=400>file=http://jornada.nmsu.edu/files/Videos/PlantPro/PlantProduction_2.flv</flashplayer>
Video from the USDA-ARS Jornada Experimental Range
Technical and Application References
- Plant Production – Harvesting
- Plant Production – Double-Sampling.