246
Plants and Plant Communities
in Crop Production. ASA Special Publication. American Society of
Agronomy, Madison, WI.
Taylor, S. E. (1975) Optimal leaf form. Perspectives in Biophysical Ecology (D. M. Gates and R. B. Schmerl, eds.) New York:
Springer-Verlag.
Taylor, S. E. and 0. J. Sexton (1972) Some implications of leaf tearing
in Musaceae. Ecology 53 : 143-1 49.
Wong, S.C., I.R. Cowan, and G.D. Farquhar (1979) Stornatal conductance
correlates with photosynthetic capacity. Nature, 282:424-426.
Problems
14.1. When T, is 30" C, air vapor pressure is 1 kPa, and wind speed is
2 mls, find the temperature of a 3 cm wide amphistomatous leaf
with stomata1 conductance on each side of 0.3 mol md2 s-I, when
absorbed radiation is Rabs = 730 w/m2.
14.2. Find reference crop evapotranspiration on a clear day with total
solar radiation of St = 825 w/m2, T, = 30" C, u = 3.5 mls, and
h, = 0.3. Assume the albedo of the reference crop is 0.2.
14.3. Use Eq. (14.16) to compare dry matter production of crops in arid
and humid environments A typical value of k for C3 crops is
O. OO5 kPa if assimilation is in kg dry mass per m
2 and transpiration is
in kg water per m
2
. Assume that the humid and arid locations both
have average maximum temperatures of 27" C, but the average minimum temperatures of the humid and arid locations are 20°C and
10" C, respectively. Using the maximum and minimum temperatures,
estimate the average maximum vapor deficit for each location.
The D in Eq. (14.16) is the average daytime vapor deficit, which is
around 0.7 times the maximum deficit. Assume 500mm (500 kg/m2)
of water is transpired for growing the crop in each location. How
much dry matter could be produced in each? For a given investment in water, is it most cost effective to irrigate crops in humid or
arid environments?
14.4. How would reducing the wind speed by a factor of two affect leaf
temperature compared to doubling the leaf size?
14.5. Under what conditions would you expect to find leaf temperature
near to air temperature?
14.6. Under what conditions of wind, radiation, air temperature, and humidity would you expect the leaf temperature to depart most from
the air temperature in a positive direction (leaf hotter than the air)
and negative direction (leaf cooler than the air)?
Plants and Plant Communities
in Crop Production. ASA Special Publication. American Society of
Agronomy, Madison, WI.
Taylor, S. E. (1975) Optimal leaf form. Perspectives in Biophysical Ecology (D. M. Gates and R. B. Schmerl, eds.) New York:
Springer-Verlag.
Taylor, S. E. and 0. J. Sexton (1972) Some implications of leaf tearing
in Musaceae. Ecology 53 : 143-1 49.
Wong, S.C., I.R. Cowan, and G.D. Farquhar (1979) Stornatal conductance
correlates with photosynthetic capacity. Nature, 282:424-426.
Problems
14.1. When T, is 30" C, air vapor pressure is 1 kPa, and wind speed is
2 mls, find the temperature of a 3 cm wide amphistomatous leaf
with stomata1 conductance on each side of 0.3 mol md2 s-I, when
absorbed radiation is Rabs = 730 w/m2.
14.2. Find reference crop evapotranspiration on a clear day with total
solar radiation of St = 825 w/m2, T, = 30" C, u = 3.5 mls, and
h, = 0.3. Assume the albedo of the reference crop is 0.2.
14.3. Use Eq. (14.16) to compare dry matter production of crops in arid
and humid environments A typical value of k for C3 crops is
O. OO5 kPa if assimilation is in kg dry mass per m
2 and transpiration is
in kg water per m
2
. Assume that the humid and arid locations both
have average maximum temperatures of 27" C, but the average minimum temperatures of the humid and arid locations are 20°C and
10" C, respectively. Using the maximum and minimum temperatures,
estimate the average maximum vapor deficit for each location.
The D in Eq. (14.16) is the average daytime vapor deficit, which is
around 0.7 times the maximum deficit. Assume 500mm (500 kg/m2)
of water is transpired for growing the crop in each location. How
much dry matter could be produced in each? For a given investment in water, is it most cost effective to irrigate crops in humid or
arid environments?
14.4. How would reducing the wind speed by a factor of two affect leaf
temperature compared to doubling the leaf size?
14.5. Under what conditions would you expect to find leaf temperature
near to air temperature?
14.6. Under what conditions of wind, radiation, air temperature, and humidity would you expect the leaf temperature to depart most from
the air temperature in a positive direction (leaf hotter than the air)
and negative direction (leaf cooler than the air)?