MATERIALS AND METHODS
Characteristics of the study area
The study was conducted in Gedarif State, which lies in the Eastern
part of the Sudan between latitudes 12.67 and 15.75°N and
longitudes 33.57 and 37.0°E, where about more than 3 000 000 ha
are put under cultivation. The soil is heavy cracking clay soils
(Vertisols), which was characterized by shrinking when dried and
swelling when moistened. The clay content ranged between 65 and
75%.