Gypsum is an amendment used to alleviate subsoil acidity. However, there are doubts about its use for acid soils that previously received applications of lime and fertilizers. There are also doubts on the use of gypsum in the cases of the use of high liming rates or for aluminum tolerant crop varieties. This paper describes a limestone and gypsum experiment conducted from 1987 to 1992 at the Tatui Experimental Station, State of São Paulo, Brazil. The experiment was on a allic, dark red, clayey latosol and had the objective to evaluate the effect of limestone and gypsum on the production of aluminum tolerant and susceptible corn cultivars, as well as the effects of the corrective agents on soil acidity. The experiment was in a split-split-plot design, with four replications in randomized blocks. In the main plots 0, 6 and 12 t ha-1 of dolomitic limestone was applied and in the subplots 0, 4 and 8 t ha-1 of phosphogypsum. In the subsubplots, aluminum tolerant and aluminum sensitive corn cultivars were grown. For the four yields obtained (the yield of 1990 was not considered) there was a statistically significant effect of limestone for both types of cultivars. Gypsum had a significant effect only for the aluminum sensitive cultivar and, in this case, the effect was additive to that of limestone, the yield increase being about one half of that produced by limestone. Liming considerably affected the soil reaction in the plow layer, increasing the pH and the contents of Ca2+ and Mg2+ and reducing the buffer extractable acidity, but it did not affect the subsoil, probably because of former applications of lime and sulfur containing fertilizers. Gypsum affected only the Ca2+ and SO4(2-) contents of the subsoil, although in a low degree, considering the amounts applied of the amendment, and did not affect soil parameters associated with acidity. It might be concluded that, even with limited effect on acidity related soil characteristics, gypsum favorably affected the production of Al susceptible corn cultivars.
acid tolerant; aluminum; cultivar; subsoil acidity; phosphogypsum