Two field experiments in 1988 and 1989 were conducted at the Fortuna Substation to evaluate levels and methods of potassium fertilization on tomato cv Duke. Applications of K2O ranging from 0 to 336 kg/ha, either banded (by hand) or through drip irrigation system (fertigation) showed no significant (P = 0.5) mean difference between treatments in tomato yield. The average tomato yield for the 1988 experiment varied from 46,689 kg/ha for the 0-K2O/ha treatment to 45,605 kg/ha for 336 kg of K2O/ha banded, and 48,617 kg/ha for 3 3 6 kg of K2O/ha in combined fertigation and banded application. In the 1989 experiment, the corresponding figures were 46,779, 47,962 and 44,060 kg/ha, respectively. The highest average tomato production in the combined 1988 and 1989 experiments was obtained with 196 kg of K2O/ha in combined fertigation and banded application, and with 252 kg of K2O/ha banded, yielding 48,095 and 48,018 kg/ha, respectively, whereas the 0-K2O treatment produced 46,707 kg/ha. The lack of significant response to K2O application seems to be the result of a high inherent available K content of the San Antón soil prevailing on the experimental site, a finding confirmed by laboratory analysis as 367 p/m.