Several extraction methods were tested but only the selected method resulted in 84.70±10.80% of extraction efficiency, and therefore results were corrected by this value. The amounts of 14C-extractable (Figure 3), i.e., the amounts of compounds readily available for action varied from nearly 17% (one application, one month) to 47% (two and three applications, one month). The amounts of 14C-non-extractable residues, which are the slow released residues because they depend on the microbial attack on the soil fraction where they are bound, varied from 19% (four applications, two months) to 29.5% (three applications, two months). Finally, the balance of total radiocarbon recovered from 14C-glyphosate varied from 80% to 103% (Figure 3), which is in agreement with Cheah et al. (1998).