| dc.description.abstract | SUI face Crusts restrict water infiltration into soil. Upon drying the surface Crust may
impede plant emergence and growth. thereby reducing yield. This study was
carried out with the aim of assessing the effect of cumulative rainfall. surface
roughness decay and slope gradient on Crust properties with a view of developing
relationships between crust formation. surface roughness and slope gradient when
soil is subjected to natural rainfall. A surface layer (0-20 em) of a chromic Luvisol
was filled into wooden boxes (1x1xO.3 rn) and arranged at an open site in a
completely randomised design. The Soil was exposed to rainfall at four slope
gradients (1%, 10%. 20% and 30%) for two rain seasons. Surface rouqhness,
crust thickness, crust strength and crust conductance were measured under
various cumulative rainfall amounts.
Thick and strong crusts were observed at the soil surface after the first rainfall
event. Crust thickness and strength were significantly different (P<0.05) between
slope gradients, with crust formation being more pronounced at lower slope
gradients (1% and 10 %) compared to higher slope gradients (20% and 30%).
Both crust thickness and crust strength followed a similar trend; as cumulative
rainfall increased, they showed a slight increase after 2-3 storms, followed by a
gradual decline as rainfall increased. Crust conductance was reduced by between
60'/'0 and 80% after the first rainfall event, and increased thereafter as the surface
crust continued to decay with rainfall increase. Crust conductance was more
strongly correlated to crust thickness (r=-0.84) than to crust strength (1=-0.54)
Saturated hydraulic conductivity of the crust correlated well with crust thickness
(r=-0.57) and crust strength (1'=-0.65). Random roughness decay was weakly
correlated to crust strength (r=0.40), crust thickness (r=0.54), and crust
conductance (r=-0.44) The rate of surface roughness decay under rainfall was
qreater at lower slope gradients (1% and 10%) than at higher slope gradients
(20% and 30(1"0). The first rainfall event had the greatest effect on crust formation
and the decay of surface roughness at all the four slope gradients
'The study concluded that Crusting occurs early in the rainfall season on freshly
ploughed soil and that crusting severity increases as the slope gradient decreases.
Therefore the study recommended that more care should be taken on flat to gently
sloping land than to steep land as far as soil crusting is concerned. Also, the soil
requires a surface cover early in the rainfall season until adequate canopy cover
develops However, the recommendations made in this study should be adopted
bearing in mind that the rainfall used in the study was from a semi-humid area and
not from the semi-arid area from where the soil samples were obtained. | en |
