Integrated Applications - Transport in the Atmosphere-Vegetation-Soil Continuum - page 278

8
Integrated Applications
This chapter shows how the knowledge from the previous chapters can be combined
to understand and manage processes at the land - atmosphere interface. First, attention
is paid to the estimation of crop water requirements using the crop factor method and
to the direct measurement of evapotranspiration using lysimeters. Then it is shown
how in a semiarid region the water productivity of irrigated crops can be studied and
improved. Finally, the response of different vegetation types (grass and forest) to heat
wave conditions is studied.
8.1 Crop Water Requirements
Evapotranspiration determines to a large extent the hydrological cycle and the envi-
ronmental conditions near the soil surface. There is a direct relation between the
ratio of actual to optimal transpiration and the ratio of actual to optimal crop yield.
Irrigation water requirements are determined by the amount of evapotranspiration
relative to the amount of natural rainfall and readily available soil moisture. Ground-
water recharge and soil salinization also depend largely on the amount of evapo-
transpiration. In the context of agricultural practice the water required to grow a crop
does not only include the water loss due to evapotranspiration, but also the water
needed to leach salts and to compensate for nonuniform application of the water
(Allen, 1998 ).
This section focuses on the application of the methods developed in the previous
chapter in the determination of crop water requirements.
8.1.1 Deinitions of Terms and Units
A confusing variety of terms regarding evaporation, transpiration and evapotranspira-
tion exists. To reduce the confusion we will list here the deinitions as they are used
here (where we mainly follow Moors ( 2002 )).
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