SOIL CRUSTING AND ITS EFFECT ON SEEDLING EMERGENCE

Crusting is commonly found in arid and semi-arid regions, As water
evaporates, soil surface becomes charged with relatively high concentration of sodic
salts; and consequently with a high ESP. The crust formation is due to two
compiementary mechanisms: (1) mechanical breakdown of soil aggregates by
beating action of raindrop, followed by compaction of a thin layer at soil surface: and
(2) chemical dispersion of clay which depends on soil ESP and electrolyte
concentration of applied water. Low organic matter content, high ESP, and high silt
content make soil surface sustainable to crusting, Soil crust has an adverse effect on
soil characteristics such as: . infiltration' and gas exchange. It also restrict the
emergence of seedtinqs ..