Agriculture Reference
In-Depth Information
80
1000
NH
4
+
990
60
Fe
2
+
980
40
970
O
2
20
960
NO
3
−
0
950
0
1
2
3
Distance from root surface (mm)
Figure 6.19
Calculated concentration profiles of O
2
,
NO
3
−
,
NH
4
+
and Fe
2
+
in a flooded
soil near a rice root after 10 days of root-soil contact. The parameter values used in the
calculations are realistic for a healthy root growing in an unexceptional lowland rice
soil (Kirk and Kronzucker, 2000). Reproduced by permission of IRRI
1.2
O
2
1.0
0.8
0.6
N
0.4
NH
4
+
NO
3
−
0.2
0.0
0
2
4
6
8
10
Time (days)
Figure 6.20
Calculated fluxes of O
2
,
NO
3
−
and NH
4
+
across the root over time. Param-
eter values as in Figure 6.19
schemes practiced for rice in parts of China and Japan, involving intermittent
drainage of water from the fields during the season (Section 7.2 and Figure 7.4).
But further research is needed to quantify how far mixed NH
4
+
-NO
3
−
nutrition
operates under field conditions and its benefits to rice growth.
6.5.2 SOLUBILIZATION OF PHOSPHATE
Deficiency of P is often the main nutrient limitation in natural wetlands, though
it is rarely important in wetland rice soils that have at least some history of P
