HETEROGENEITY, PLOT SHAPE EFFECT AND OPTIMUM PLOT SIZE

By introducing heterogeneity indices, an empirical equation is propose d for characterizing the heterogeneity of non-isotropic fields. The fo rmula is an extension of Fairfield Smith's (1938) empirical law descri bing heterogeneity in isotropic fields. Based on these indices, criter ia are provided for choosing optimum plot shapes in terms of minimizin g the sample variance and cost. Sample plots having their largest dime nsion in the direction with the largest index will give more accurate results (less variable) than plots with other shapes. Relations betwee n the optimum plot size and relative cost versus variogram parameters are given for several variogram models. These relations indicate that variograms with small effective ranges have a very profound effect on the optimum plot sizes.