The Hydrothermal Soil Regime under Gum Arabic Trees [Acacia senegal (L.) Willd.] in Al-Rawashda Forest, Al-Gedarif State, Sudan*

Abstract

The study was undertaken to generate broad-base data on the
hydrothermal regimes in a Vertisol under Acacia senegal in Al Rawashda
forest, 35 km northeast Al-Gedarif town. The indicators measured for
describing the moisture regime were rainfall, infiltration and evaporation
rates from U.S. Class A pan, soil moisture storage and actual
evapotranspiration. In 1997, the total rainfall was 403 mm, 48% was
received in August and 82% was received in July, August and September.
The soil was fully recharged with moisture during June-September,
depleted and desiccated during October-March and started to rewet in
April-May. The daily evaporation ranged from 2.9 to 5.6 mm in autumn,
7.5 to 13.6 mm in winter and 12.8 to 16.0 mm in summer. The soil
moisture storage was lowest in 14th May and highest in 5 th September,
1997. Although rainfall reduced the vapour pressure gradient, it increased
the availability of water to the evaporating site and consequently
increased evaporation. Thus, mean monthly evaporation (Em, mm)
increased significantly (P = 0.05) with increase of mean monthly rainfall
(Rm, mm) as shown by the following power relationship: Em = 1738 Rm
0.5402 (r2 = 0.790). The pooled infiltration rate (IR) as a function of time
for the two sites in three successive months’ best fitted the following