Page 173 - Arabian Studies (II)

Effects of Irrigated Agriculture on Soil Characteristics 165

by the expansion of agriculture, so that more saline water was being
tapped. However, the quality of the irrigation water has not further
deteriorated and the trend may even have been reversed. The area in
which pit 7 was located was capable of growing squashes and melons
in 1967, but by 1969 soil salinity in the topsoil had increased to such
an extent that the plot had been given over to the cultivation of tree
species, notably Tamarix spp, for windbreaks and amenity areas. A
single topsoil sample (4—10 cms.) taken by the author in 1969 from
this plot had a conductivity of 7.4 mmhos./cm. at 25°C.
The halosols which occupy the area of the former extension of the
Ras al-Khaimah lagoon have not been used extensively for cultiva­
tion. These soils are poorly draining, with standing water frequently
being observed on the surface and their permeability is not only
affected by the silty nature of their texture but also by the high
levels of exchangeable sodium (e.g. profile 9, Table 4). Profiles
usually have conductivities in excess of 10 mmhos./cm. at 25° C.
while the levels of exchangeable sodium remain relatively constant
throughout the profile, with ESPs above 25. Their carbonate
contents of 45—60 per cent are similar to those of the deposits
forming the Jiri Plain. However, along the eastern edge of the lagoon,
more recent outwash of highly calcareous, but non-saline character
have been deposited over lagoonal sediments as in the case of profile
10 (Table 4). Some of these soils have been taken into cultivation as it I
the surface deposits are relatively freely draining, have low ESPs and
low conductivities. There is, however, impedance caused by the
underlying horizons being of heavier texture and after a number of
years these soils have gone out of cultivation. While the amounts of
soluble salts in the surface horizons may have been leached into the
lower horizons of the soil solum, there has been a build up in the
level of exchangeable sodium to a greater extent than prior to
cultivation through the use of irrigation waters having a high
alkalinity hazard. In some instances, ESP levels of 30—35 per cent
have been recorded and these are intolerable for crop cultivation.
In addition, as agriculture expands, some farmers have attempted
to cultivate some of the poorer drained halosols. This situation is
exemplified by profile 11 (Table 4) which was on the point of being
taken out of cultivation in 1967. In such soils the levels of both
salinity and alkalinity are beyond those generally accepted for crop
cultivation and while crops such as beans, radishes and tomatoes
might yield for a year or two, agriculture soon becomes impossible.
Much of the disused agricultural land in Ras al-Khaimah is of this type.
For commercial agriculture to be successful in Ras al-Khaimah the
xerosol soils of the Jiri Plain offer the best potential. Over the last