Agriculture Reference
In-Depth Information
Example 7.2
In an experimental field of rice crop, water sampler was installed at 120 cm depth
to collect the deep drainage and analyzed at laboratory for NO
3
-N concentration.
Nitrogenous fertilizer was applied in two splits. Water samples were collected at 15-
day intervals and deep drainage was estimated using field water balance approach.
The sampling was done during the crop season and continued for a month after the
crop harvest. The following data were gathered:
DAT
15
30
45
60
75
90
105
120
135
150
Estimated
drainage (mm)
30
25
20
18
22
20
20
24
30
31
Conc. of NO
3
-N
in water (mg/l)
3
2.5
4.2
2.2
4
2.3
2.7
4
5
4
Determine the amount of NO
3
-N leached per hectare during the period.
Solution
Drainage volume from a particular drainage event, say 15 DAT, per hectare
=
10,000 m
2
300 m
3
(30/1,000) m
×
=
10
6
)cm
3
Then,
solute
amount,
M
s
=
V
d
×
C
s
=
(300
×
×
(3/1,000)/1,000 g/cm
3
10
6
)
(3/10
6
)
=
×
×
=
(300
900 g
DAT
15
30
45
60
75
90
105
120
135
150
Estimated
drainage (mm)
30
25
20
18
22
20
20
24
30
31
Drainage vol.,
m
3
/ha
300
250
200
180
220
200
200
240
300
310
Conc. of NO
3
-N
in water (mg/l)
3
2.5
4.2
2.2
4
2.3
2.7
4
5
4
Solute (NO
3
-N)
amount (g)
900
625
840
396
880
460
540
960
1,500
1,240
Thus, total NO
3
-N leached
=
8,341 g/ha
=
8.34 kg/ha
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