Environmental Engineering Reference
In-Depth Information
1995, Wild 1995). The assessment of the plant available P should consider soluble P
concentrations in soil.
Recommendations with respect to different types of crops and corresponding
nutrients' uptake rate is presented in Table 10.2. These could serve as a guideline during
the design of the irrigation field and the determination of the nutrients loadings.
The continuous long-term application of P at levels exceeding crop requirements
(Table 10.2) increases the potential for P loss through runoff and drainage water leading
to the eutrophication of surface water
Table 10.2. Nutrients' uptake rate by selected crops.
Crop
Nutrients' uptake rate (kg/ha.yr)
Nitrogen
Phosphorous
Potassium
Forage crops
Alfalfa
225-540
22-35
175-225
Bermuda grass
400-675
35-45
225
Reed canary grass
335-540
40-45
315
Field crops
Barley
125
15
20
Corn
175-200
20-30
110
Grain sorghum
135
15
70
Cotton
75-110
15
40
Potatoes
250
10-20
30-55
Selected from Metcalf & Eddy (1991)
bodies. However, excessive P has not been a problem for irrigation purposes and no
guideline value is given for its evaluation.
3.3
Toxic metals
The concern with respect to the impacts of toxic metals on public health, soils, ground
and surface water has been discussed in previous chapters. From the point of view of
crops irrigation, the most hazardous trace elements are Cd, Zn and Pb (Wild 1995). This
is due to three factors:
• They accumulate in the edible portions of crops;
• They easily enter the food chain;
• They form part of many products, used widely in the every-day life, and consequently,
their concentrations in wastewater are relatively high.
Although a high trace metal concentration poses a health hazard, few fatalities due to the
ingestion of trace metals have been traced to the contamination of soils (Wild 1995). Of
