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world’s total. The situation differs a little bit in the case of non-irrigated cultivated area
drained. Approximately a quarter of drained non-irrigated land area all around the world
is in the COMCEC Member Countries. The detailed information is given in Annex 9.
When an evaluation is made as of drainage requirement, it is necessary to drain
the irrigated and non-irrigated lands completely in terms of both environmental health
and sustainable agricultural production. For that reason, when soil salinity is concerned,
it is very important to establish the necessary drainage systems in the COMCEC Region
where needed.
In addition to drainage, other important problem facing in irrigation is
salinization. Salinization is a process involving an accumulation of salt in topsoil and is
of particular concern in irrigated arid and semi-arid regions. Salinization is usually
associated with elevated water tables, which transport dissolved salts to the soil surface.
Water tables rise gradually when the hydrologic balance of the system is disrupted
through removal of deep rooted native vegetation or application of irrigation water.
Once the water table nears the soil surface, a disturbance such as heavy irrigation or
rainfall can draw water levels into the root zone, where evapotranspiration by plants
quickly aspirate salts to the soil surface. Soil salinization appears suddenly, immediately
impeding crop growth and imposing long term limitations on land productivity (Siebert
et. al., 2010). Salinization is a worldwide problem, particularly acute in semi-arid areas
which use lots of irrigation water, are poorly drained, and never get well flushed. These
conditions are found in parts of the Middle East, in China's North Plain, in Central Asia,
in the San Joaquin Valley of CA, and in the Colorado River Basin; all areas where the
soil profile never (or rarely) gets well flushed (FAO, 2002).
Figure 10.2 shows the distribution of soil salinity in areas equipped with fully
controlled irrigation in the world. This Figure realizes that about 20% of fully controlled
irrigation area is salinized in the world. LDC, OECD and Developed (DEV) countries
have salinized areas below the world rate. On the contrary, the COMCEC Member
Countries have 20% of the world’s total salinized area.
In general, when soil salinity is considered, value of the COMCEC Region is
above the world’s average. The factors such as climate, topography, wrong agricultural
policies and production systems cause the area of saline-affected lands to increase.