Environmental Engineering Reference
In-Depth Information
Phosphorous (P) applied on cropland could be taken up by plants, incorporated into
soils as organic P, or could become weakly or strongly adsorbed onto clay particles and
fixed by Al, Fe and Ca ions, depending on the soils' pH. After initial adsorption, there is
a gradual fixation of added P that renders part of it unavailable to plants. With regular P
application, the importance of the fixation process is diminished, as the soil P-sorption
capacity becomes slowly saturated, and a larger P concentration remains in soils in
soluble
Table 10.1. Recommended concentrations of
selected parameters in wastewater reused for
irrigation.
Parameter
Level of restriction for irrigation reuse
None
Slight to Moderate
Severe
EC (deciSiemens/m at 25ºC)-in respect to salinity
< 0.7
0.7-3.0
> 3.0
EC (deciSiemens/m at 25ºC)-in respect to soil permeability
SAR
2
= 0-3
< 0.2
0.2-3.0
> 3.0
SAR
2
= 3-6
< 0.3
0.3-1.2 >
1.2
SAR
2
= 6-12
< 0.5
0.5-1.9
> 1.9
SAR
2
= > 12
< 2.9
2.9-5.0
> 5.0
TDS (mg/l)
< 450
450-2000
> 2000
Sodium
Surface irrigation (meq/l)
< 3.0
3.0-9.0
> 9.0
Sprinkler irrigation (meq/l)
< 3.0
> 3.0
-
Sprinkler irrigation (mg/l)
< 70
> 70
Chloride
Surface irrigation (meq/l)
< 4.0
4.0-10.0
> 10.0
Surface irrigation (mg/l)
< 140.0
140.0-350.0
> 350.0
Sprinkler irrigation (meq/l)
< 3.0
> 3.0
Sprinkler irrigation (mg/l)
< 100.0
> 100.0
Boron (mg/l)
< 0.7
0.7-3.0
> 3.0
Nitrate nitrogen (mg/l)
< 5.0
5.0-30.0
> 30.0
Bicarbonate (meq/l)
< 1.5
1.5-8.5
> 8.5
form. In a study of the behavior of P in soils, it was noted that after 6 months of P
application, the plant available P decreased from 47 to 27 % due to the fixation by clay,
organic carbon, iron (Fe), aluminum (Al) and calcium carbonate (Muchovej & Rechgil
