Agricultural limestones of various PRNT (Relative Power of Total Neutralization) values, calculated considering the relative efficiency of their granulometric fractions, were used in a comparative study. A number of 22 limestone samples were collected ; 12 from different mills from the municipalities of Rio Claro, Piracicaba and Tietê and 10 selected to obtain a desired range of granulometric and chemical composition in the lot. The results indicate that PRNT formulas currently used in Brazil may be underestimating limestone efficiency. The proposed new formula can be taken as a more reliable index for agricultural purposes.
limestone; PRNT