Effect of gypsum on seedling emergence in a kaolinitic crusting soil

The emergence capability of maize seeds in a kaolinitic red tropical soil 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 cracked areas; they also showed a lower bulk density and a higher residual moisture content in air-dry condition. Gypsum translocation was limited to the first millimeters of the soil. A possible explanation advanced is the loss of brittle behaviour in treated samples, due to greater retention of clay in the surface soil layer, non-brittle behaviour by the treated soil would hamper soil cracking by emerging seeds and their emergence through cracks.