Agriculture Reference
In-Depth Information
40
Air
Water
Soil 0-2 cm
Soil 2-10 cm
35
30
Rice crop
Rice crop
25
0
100
200
300
Day of year
Figure 5.8
Temperatures in ricefields over a year, IRRI, Laguna, Philippines. Values
are means over a month; air temperature is maximum; water and soil temperatures were
taken at 1400 h (Roger, 1996). Reproduced by permission of IRRI
1.0
0.8
0.6
0.4
0.2
0.0
0
20
40
60
80
100
Time after transplanting (days)
Figure 5.9
Decrease in light penetration to the floodwater as a typical rice crop develops
(J. Sheehy, IRRI, unpublished data)
only 10% of the incident photosynthetically active radiation reaches the flood-
water. Similar changes occur in natural wetlands as plants become established
following inundation.
Dissolved O
2
and CO
2
and pH
Oxygen is produced by photosynthetic organisms in the water and consumed
in respiration and other oxidative processes. Often the concentration varies from
super-saturation during the day to near zero at night. Because the partial pressures
