Crusting soils cover in Zimbabwe only about 1 ("4, of the total surface but are located mostly in the intensive commercial agriculture areas. Soil surface crusting can lead to runoff and erosion because of decreasing infiltration and seed emergence. Crusting mainly results from breakdown of clods at the soil surface during the successive rainfall events. The purposes of this work were (1) to assess the structural stability by determining the proportion of water stable aggregates resulting from various breakdown treatments and (ii) to evaluate the evolution of the soil structure by investigating the micromorphological characteristics and the carbon and/or Fe and Al oxide content of the stable aggregates. Samples from the Ap and Bt horizons of a tilled crusting soil, in Mazowe area (near Harare, Zimbabwe), were compared with samples from the A horizon of an uncultivated neighbouring soil. The Bt horizon was investigated because it showed a more developed structure then the Ap horizon, although there was no important differences of properties. Av,gegate stability measurements showed that the Ap horizon of the cultivated soil had very weak structural stability, while the Bt horizon of the cultivated soil and the A of the uncultivated horizon were more stable. Micromorphological observations using backscattered electron scanning images (BESI) on polished thin-section of stable aggregates or aggregates fragments resulting from the different stability test., and mercury intrusion porosimetiy, evidenced, in cultivated horizon, in comparison with uncultivated ones, a higher volume for pores formed by the decrease of clay and cementing substances located between silt and sand particles. This situation, leading to a more open structure, decreases the aggregate stability in Ap horizon and therefore promotes crust formation. The stability of the Bt horizons was attributed to a higher clay and Fe and Al oxide content and, to a lesser extent, to the organo-mineral complexes which also play an important role in the A horizon of the uncultivated soil.
Studies on soil water aggregates stability and structure of a crusting soil from Zimbabwe
D'Acqui LP;
1996
Abstract
Crusting soils cover in Zimbabwe only about 1 ("4, of the total surface but are located mostly in the intensive commercial agriculture areas. Soil surface crusting can lead to runoff and erosion because of decreasing infiltration and seed emergence. Crusting mainly results from breakdown of clods at the soil surface during the successive rainfall events. The purposes of this work were (1) to assess the structural stability by determining the proportion of water stable aggregates resulting from various breakdown treatments and (ii) to evaluate the evolution of the soil structure by investigating the micromorphological characteristics and the carbon and/or Fe and Al oxide content of the stable aggregates. Samples from the Ap and Bt horizons of a tilled crusting soil, in Mazowe area (near Harare, Zimbabwe), were compared with samples from the A horizon of an uncultivated neighbouring soil. The Bt horizon was investigated because it showed a more developed structure then the Ap horizon, although there was no important differences of properties. Av,gegate stability measurements showed that the Ap horizon of the cultivated soil had very weak structural stability, while the Bt horizon of the cultivated soil and the A of the uncultivated horizon were more stable. Micromorphological observations using backscattered electron scanning images (BESI) on polished thin-section of stable aggregates or aggregates fragments resulting from the different stability test., and mercury intrusion porosimetiy, evidenced, in cultivated horizon, in comparison with uncultivated ones, a higher volume for pores formed by the decrease of clay and cementing substances located between silt and sand particles. This situation, leading to a more open structure, decreases the aggregate stability in Ap horizon and therefore promotes crust formation. The stability of the Bt horizons was attributed to a higher clay and Fe and Al oxide content and, to a lesser extent, to the organo-mineral complexes which also play an important role in the A horizon of the uncultivated soil.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
