Table 4. Specific water uptake rates for some tropical and
temperate species (after Rendig and Taylor 1989).
Water
uptake rate
(m3 m1 s1)
Species
Source
5 1012 to
5 1011
Cotton
Bar-Yosef and Lambert (1981)
<1 1014 to
8 1012
Taylor and Klepper (1975)
1 1012 to
2 1011
Field pea
Hamblin (1985)
3 1012 to
8 1012
Lupin
Hamblin (1985)
3 1012 to 2.4 1010
Corn
Allmaras et al. (1975)
1 1012 to 2.4 1011
Taylor and Klepper (1973)
8 1012 to
1 1010
Oats
Ehlers et al. (1980)
2 1011 to 3 1010
Soybean
Allmaras et al. (1975)
2 1012 to 3 1010
Willatt and Olsson (1982)
2.8 1011 to 2.2 1010
Willat and Taylor (1978)
1 1012 to
2 1012
Wheat
Greacen and Hignett (1976)
4 1013 to
1 1012
Spring
Hamblin (1985)
2 1013 to
2 1012
Winter
Gregory et al. (1978)
about 1 1012
Temperate
Welbank et al. (1974)
grasses
50
Cortex
Intact
Removed
40
Nutrient Solution
Sand
30
20
10
0
10
20
30
40
50
Plant Age (DAP)
Figure 7. Effect of plant age on the hydraulic conductivity of hydro-
ponically grown and sand-grown cotton roots (after Brar et al. 1990b).
they are grown under identical conditions (Table
of the 24, 36, and 48 DAP. Hydraulic conductivity
4). For example, lupin and wheat were grown at
of sand-grown roots was 4 to 10 times lower than
the same location and time, yet their maximum
that for roots grown hydroponically, whether
uptake rates were 2 109 and 1 1012 m3 m1 s1,
conductivity was compared at equal DAP or at
respectively. Root uptake models often assume that
equal root length (Table 5).
hydraulic conductivity of the root system is a con-
stant at all plant growth stages. Conversely, Brar et
Nutrient uptake
al. (1990b) reported that hydraulic conductivity of
Nutrient uptake is related to diversity in nutri-
young cotton roots changed with plant age (Fig. 7).
ent mobility in soil as well as the surface charac-
Hydraulic conductivity decreased 45% in nutrient
teristics of the roots. Root length, root radius, and
solution-grown roots and 57% in sand-grown roots
surface area are the important characteristics of
between 12 days after planting (DAP) to the mean
the roots that determine the rate of nutrient up-
8
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