Page 166 - Arabian Studies (II)

158 Arabian Studies II

these support stands of Prosopis spicigera trees. These stands arc able
to survive because the heavier texture of the soils allows moisture to
be retained for much longer periods of the year. In both types of
xcrosols, pedogenic horizons are weakly developed.
Halosols occur in two distinct situations. The main area represents
the former extension inland of the Ras al-Khaimah lagoon. Solonetz
(saline-alkaline) soils predominate and in addition to conductivities
often in excess of 10 mmhos./cm. at 25°C., the exchangeable sodium
percentage (ESP) frequently exceeds 25. These soils are of heavy
texture, have a low permeability and are consequently moist for the
entire year. They occupy the lowest parts of the landscape but
coarser textured halosols are associated with the slightly higher
ground on the edges of the outwash fans. Halosols are also found on
the Jiri Plain. On air photographs they appear as dark patches, devoid
of vegetation, in discontinuous strips which probably represent
eroded remnants of the soil outwash fans partially covered by more
recent deposits. These halosols tend to be of coarse texture and are
of the solonchak (saline) type and further south on the Gharif Plain
may contain gypsic horizons.
Yermosols and regosols are also present in Ras al-Khaimah.'The
former are found on the outwash fans adjacent to the Ru’us-al-Jibal
highlands. These outwash fans are mainly composed of coarse
rudaceous deposits with carbonate contents well in excess of 50
per cent, reflecting the origin of the outwash in the limestone
uplands. Pedogenic horizons are even more weakly developed than
with the xerosols, moisture retention is very low, but organic matter
contents of the soil are usually in excess of 0.25 per cent due to the
scattered Acacia bushes and annual grass species. The former have
extensive root systems and are able to tap the deeper moisture while
the grass species are associated with the seasonal wadis. In contrast,
the regosols are associated with the sand dunes of the Desert
Foreland. Vegetation is very sparse and organic matter contents are
less than 0.25 per cent. Single grain structure predominates, profile
morphology is lacking and the ‘soils’ are subject to windblow.
(ii) The Effects of Date Cultivation on Yermosol/Xerosols
In contrast to other parts of the Arabian Peninsula, the date gardens
of Ras al-Khaimah, particularly those between Hail and Shimal, are
well tended. There is little evidence of disease while few of the trees
are old. The palms are spaced at sufficient intervals to allow full
development of the palm to take place. The date gardens are located
on the edges of the outwash fans where the coarse rudaceous
outwash has some finer material deposited on top, the soils being
classified as either yermosols or xerosols.