This research was aimed at evaluating the heterogeinity index the most important chemical characteristics (phosphorus, effective cation exchange capacity, potassium, organic matter, magnesium, H+Al and pH) of a soil inside a plastic greenhouse and to determine the sample size, fallow and immediately after two cropping. The heterogeinity index was estimated through the Smith method. For all vaiables analised the heterogeinity index was low and the optimum sampling size was equal to one basic unit, that is, one sampling point for both cropping systems. Considering a half amplitude of the confidence interval in percentage of the mean equal to 20% and a 5% error confidence level, the sampling size is equal to 11 sampling points as representative for all variables analyzed for a soil both under fallow or after cropping.
heterogeneity index; plot size; sample size; modified environment
