Vegetation: Transport Processes Inside and Outside of Plants - Transport in the Atmosphere-Vegetation-Soil Continuum - page 236

Table 6.5 Application of Eq. ( 6.35 ) for three crops grown at two locations:
Göttingen (Germany) and Akron (Colorado)

Crop μ Location VPD WP T Yield

expectation

Transpiration Predicted

yield from
300 mm

Pa Pa kg m -3 t ha -1 mm t ha -1

Maize 9.1 Göttingen 900 10.1 20 198 30.3

Akron 1900 4.8 418 14.4

Wheat 4.5 Göttingen 900 5.0 15 300 15.0

Akron 1900 2.4 633 7.1

Faba
bean

3.1 Göttingen 900 3.4 10 290 10.3

Akron 1900 1.6 613 4.9

For a given value of expected yield the transpirational water use is calculated. Also the yield is
calculated at 300 mm water extracted by roots. The yield is total above-ground biomass.
After Ehlers and Goss ( 2003 ).

The environmental conditions for plant production have an ironic aspect. In dry
and arid areas with bright sunshine and high radiation for photosynthesis, the amount
of soil water stored is normally low; nevertheless a comparatively large quantity of
water is needed for the production of biomass. The scarceness of water limits the
production level, while the dry atmosphere lowers the eficiency of transpirational
water use. In wet and humid areas, however, frequently having less incoming radia-
tion, the demand of water supply is less, as the eficiency of water use in production
is greater (Ehlers and Goss, 2003 ). On the other hand, the actual supply may be so
abundant that the surplus can have a harmful effect on plant growth and develop-
ment.

6.6 Microclimate
The meteorological conditions within a vegetation may be very different from those
above the vegetation. Because the processes in the plants react to the local conditions
and because the conditions above the canopy are inluenced by processes inside the
canopy, it is worthwhile to discuss a number of aspects of the microclimate inside the
canopy.
For any of those aspects the architecture of the vegetation is important. This not only
entails the height of the vegetation, but also the size of the leaves, the orientation of the
leaves and the vertical distribution of the leaves. The latter determines to a large extent
at what height the active level of the vegetation is located (at what height most of the