EFFECT OF GYPSUM ON SEEDLING EMERGENCE IN A KAOLINITIC CRUSTING SOIL

The emergence capability of maize seeds in a kaolinitic red tropical s oil from Zimbabwe, subjected to rainfall simulation, was investigated under three kinds of treatment: untreated, 2.5 T . ha(-1) and 5 T . ha (-1) of phosphogypsum. Samples treated with gypsum exhibited a strong increase of crust strength and a decrease of the percentage of the cra cked areas; they also showed a lower bulk density and a higher residua l moisture content in air-dry condition. Gypsum translocation was limi ted to the first millimeters of the soil. A possible explanation advan ced is the loss of brittle behaviour in treated samples, due to greate r retention of clay in the surface soil layer, non-brittle behaviour b y the treated soil would hamper soil cracking by emerging seeds and th eir emergence through cracks.