The modification of `the nearest neighbour' method for using various size plots in field trials has been developed and the results of testing its validity by computer simulation are presented . It was found that the Field-S variant of this method using a square pilot area is the best for fields with a low and medium spatial heterogeneity . The Field-L variant using the least quantity of neighbours, offers advantages for fields with a medium and high spatial effect .The optimal values of the controlling coefficients of these variants were computed to allow for the calculation of the environmental indices over a wide interval of spatial heterogeneity with sufficient accuracy . For this reason, this local adjustment method is recommended as an obligatory statistical procedure for a prior data analysis of any field experiments that have fulfilled the necessary requirements . The original Field and CRBSD programs using the local adjustment method developed have been created for IBM-compatible personal computers .