Adequate Sample Size and Appropriate Sampling Method for Estimating Grassland Production through Simulation

— One of the important factors in proper rangeland management is determination of grazing capacity which is related to accurate and precise estimation of forage production. As the estimation of forage production is only possible through sampling, so that determination of adequate sample size and suitable sampling method are the main objective of our applied research. The sampling was conducted in five locations in northern grasslands of Iran. In each location, two microplots of 64 m 2 were established based on international protocols. By combining the data of five locations, a layout of 640 m 2 was simulated in R software. This layout is considered as our statistical population. Primary sample sizes of 20, 25, 30, 35, and 40 were selected and by using different allowable errors with the lowest coefficient of variation, adequate sample sizes of 60 and 120 were obtained. These plot sizes were used to compare the accuracy and precision of methods including random, systematic, random–systematic, two-stage, and stratified sampling. The results showed as the allowable errors are decreasing, the sample sizes are increasing. In general, the mean of stratified sampling is almost equal to the actual mean of the population, indicating its higher accuracy and precision in comparison to other methods. Sample size of 60 and stratified sampling method with 3 to 5 strata were our ultimate selections.