Environmental Engineering Reference
In-Depth Information
of highly productive agricultural systems. In the following, some main agricultural
aspects of wastewater irrigation are summarized and a new, agroecological, per-
spective on the topic is proposed.
3.2 Water Quality Considerations for Agricultural Use
of Wastewater
Whether a (waste)water resource is suitable for agricultural irrigation depends on a
range of factors concerning crops, soils, climate, agricultural practices, etc. This
means that the same quality water might not pose a problem in one context while
being un
t for irrigation in another. Hence, while standards (see Annex 2) can give
a rough indication of the suitability of a given water resource for irrigation, they
cannot replace experimenting in the respective speci
c context.
In the following, a few of the main irrigation water quality considerations are
brie
y described.
3.2.1 Salinity
The main concern with regard to water quality from an agricultural point of view are
salt concentrations (Ayers and Westcot
1985
; Tanji and Kielen
2002
). The major
chemical elements constituting salinity are sodium, calcium, magnesium, potassium,
bicarbonate, sulphate, chloride and nitrate. The most common lump parameters of
salinity give concentrations in electrical conductivity (EC) in decisiemens per metre
(dS/m) or TDS (total dissolved solids) in milligrams per litre (Tanji and Kielen
2002
). The degree of salinity stress in plants depends on several factors.
Although yield reductions are defined as a function of the average salt concentration in the
rootzone, interactions between soil, water and climatic conditions influence the relationship.
Exceedingly high air temperatures may cause a reduced salt tolerance. Cultural practices
also determine to a certain extent yield reduction resulting from salinity stress. Other plant
characteristics (which differ between plant species, varieties of the same species and growth
stages during which salinity stress occurs) determine their ability to cope with salinity stress
(Tanji and Kielen
2002
: 42).
Many crops are most sensitive to salinity in their early growth stages. A strategy
for their cultivation is for farmers to use water with lower salt content (or waste-
water mixed with such water) for the
first crop irrigations (Tanji and Kielen
2002
).
The tolerance of plants to levels of contaminants differs signi
cantly between
species. Some plants can take up large amounts of salt, as well as heavy metals and
other toxic elements (Tanji and Kielen
2002
; Simmons et al.
2010
). A list of
selected salt-tolerant plants is given in Annex 3. Salt tolerance differs furthermore
between different varieties of the same species and between different growth stages
of the same plant.
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