Long-term effects of gypsum on crop yield and subsoil chemical properties

In hot humid climates with highly leached, variable charge soils, the yields of many crops are limited due to subsoil acidity. Although surface-applied gypsum has been shown to be effective in ameliorating this acidity in ferruginous and aluminous soils, the length of time that the effect is likely to last has not been satisfactorily established. ii number of long-term experiments with gypsum incorporated into the topsoil at 10 and 35 Mg ha(-1) were sampled to evaluate its effects on soil profile chemical properties and yields of corn (Zea mays L,) and alfalfa (Medicago sativa L.). Even after 16 yr, the gypsum effects were still clearly risible. Exchangeable Ca and SO4 were higher down the soil profile in the gypsum than in the control treatment. A complementary reduction in exchangeable Al was observed in the gypsum treatment to the 80-cm depth, However, pH was not greatly altered down the profile. This amelioration of the effects of subsoil acidity was reflected in improved crop yields of both corn (29-50%) and alfalfa (approximate to 50%) on the gypsum treatments, Because the gypsum effect is so long-lasting, its use as a subsoil acidity ameliorant becomes highly economic because the initially high cost can be amortized over an extended period of time.