Environmental Engineering Reference
3.2.2 Water Infiltration into the Soil
ltration of water that is too slow or to fast can represent a major problem for
irrigated agriculture. It depends to a large extent on soil characteristics such as the
degree of soil compaction, soil structure, organic matter content and the general
chemical make-up (Ayers and Westcot 1985 ). However, the quality of the irrigation
water also plays a role for the rate of water in
ltration. The most relevant water
quality factor with regard to in
ltration is the sodium content in relation to calcium
and magnesium. Under conditions of sodicity (a high proportion of sodium), the
ltration is reduced. The most common indicator used to
assess sodicity of water and soils is the Sodium Adsorption Ratio (SAR). It
describes the content of sodium in relation to the calcium and magnesium content.
For reference values on SAR, see Annex 2.
is capacity for water in
3.2.3 Toxic Elements
Besides salts, there is a range of other chemical elements that can pose problems for
plant growth. The most common phytotoxics in municipal wastewater besides
sodium are boron and chloride (Pescod 1992 ; Bauder et al. 2011 ). A list with
threshold values of phytotoxic elements that may be present in wastewater is given
in Annex 2. There are also some emerging issues on antimicrobial drug resistance,
related to wastewater, which will need further research.
Nutrient requirements of a plant depend on the growth stage with, for example
higher nitrogen demand in early stages of growth than in
flowering and fruiting
stages (WHO 2006b ). Excessive nutrient supply can damage some crops, e.g. by
leading to a plant growth that is too fast (cf. Pescod 1992 ).
3.3 Crops Irrigated with Wastewater
Which crops are grown under wastewater irrigation in an area depends on the
respective local context. On the one hand, some restrictions apply to different plants
tolerance to water quality. On the other hand, for many plants, wastewater seems to
pose relatively few problems from a phytosanitary point of view as it consists of
99 % water (Raschid-Sally 2010 ). In fact, studies in India and Pakistan found similar
or even higher levels of crop diversity in areas irrigated with wastewater compared to
areas irrigated with other water types (Jacobi et al. 2009 ; Weckenbrock 2010 ).
The most common crop types under wastewater irrigation are (in declining
order) vegetables, cereals and fodder crops (Raschid-Sally and Jayakody 2008 ).