Agriculture Reference
In-Depth Information
Table 8.5 Mean concentrations of major and minor fertilizer elements in the
irrigation water during the rainy (wet) season, 2005
Sampling site
Concentration (mg/l)
NH 4
NO 2
NO 3
PO 3
4
K þ
Ca 2 þ
Mg 2 þ
SO 2
4
Na þ
Cl 2
ENDA
0.87
(0.77)
0.13
(0.09)
232
(182)
13
(10)
597
(149)
2.0
(1.7)
0.5
(0.5)
18
(11)
0.40
(1.06)
203
(97)
ENDM
0.97
(0.86)
0.13
(0.08)
265
(362)
10
(10)
68
(184)
2.3
(2.1)
0.5
(0.9)
17
(11)
0.41
(0.28)
182
(94)
EPP
0.42
(0.45)
0.08
(0.09)
209
(356)
19
(11)
831
(1158)
1.7
(1.7)
0.6
(2.3)
16
(17)
0.30
(0.21)
80
(34)
EET
0.49
(0.53)
0.12
(0.22)
236
(280)
12
(15)
1237
(754)
2.8
(2.7)
0.8
(2.2)
13
(11)
0.16
(0.15)
37
(38)
EMA
1.04
(1.11)
0.33
(0.65)
285
(1445)
9
(15)
1076
(1433)
1.5
(2.6)
0.8
(0.9)
14
(17)
0.26
(0.34)
85
(60)
EPNA
1.28
(0.45)
0.27
(0.15)
264
(172)
13
(13)
862
(861)
2.1
(2.8)
0.7
(1.0)
14
(6)
0.21
(0.22)
56
(46)
EPA
0.46
(1.39)
0.15
(0.18)
219
(371)
14
(11)
910
(1326)
1.9
(2.8)
0.7
(0.76)
10
(17)
0.22
(0.20)
53
(50)
ERO
0.49
(0.83)
0.09
(0.10)
236
(233)
11
(12)
51
(133)
1.9
(1.9)
0.6
(0.6)
15
(11)
0.13
(0.14)
40
(28)
EJE
0.29
0.12
230
10
19
0.7
0.3
18
0.48
85
ED
0.54
(0.95)
0.09
(0.10)
233
(217)
12
(11)
762
(1243)
1.8
(3.0)
0.5
(0.9)
7
(7)
0.41
(0.25)
43
(33)
concentration of nitrites. An acidic milieu favours this bioconversion. When
nitrites are present, haemoglobin can be oxidized to methaemoglobin, which
cannot carry oxygen and causes methaemoglobinaemia. This is very
dangerous for children. In a weakly acidic milieu, nitrites are converted into
nitrosamines, which have been found to be carcinogenic (Klein, 1973;
Musibono, 1992; WHO, 2000).
Minor fertilizer elements in the irrigation water. Calcium (Ca),
magnesium (Mg), sulphur (S) and sodium (Na) are necessary macronutrients
for crops. Irrigation water can also carry these elements in significant
quantities. The concentrations we found in our study of these elements in
irrigation water are given in Table 8.5. Concentrations of Ca and Mg were
low in both seasons, although Mg levels were somewhat lower during the
rainy season. The Ca and Mg values indicated that the water was soft.
Heavy metals in the irrigation water. Several heavy metals are found in
wastewater contaminated by industrial pollution. Some of the more
commonly found heavy metals include Pb, Cd, chromium (Cr), cobalt (Co),
nickel (Ni), copper (Cu), zinc (Zn) and molybdenum (Mo). The average
concentrations of Pb, Cd, Cr, Co, Ni and Cu are recorded in Table 8.6. The
concentrations of Pb and Cd were generally higher in the rainy season than in
the dry season. The concentrations of Pb for all samples were less than 5mg/l,
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