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| Titel |
An analytical solution for the estimation of the critical available soil water fraction for a single layer water balance model under growing crops |
| VerfasserIn |
N. Brisson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 2, no. 2/3 ; Nr. 2, no. 2/3, S.221-231 |
| Datensatznummer |
250000350
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| Publikation (Nr.) |
 copernicus.org/hess-2-221-1998.pdf |
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| Zusammenfassung |
| In the framework of simplified water balance
models devoted to irrigation scheduling or crop modelling, the relative transpiration rate
(the ratio of actual to maximal transpiration) is assumed to decrease linearly when the
soil dries out below a critical available water value. This value is usually expressed as
a fraction, F, of the maximal available soil water content. The present work aims to use
the basic laws governing water transfer through the plants at a daily time step to compute
F dynamically as the crop grows. It can be regarded as an expansion of Slabbers' (1980)
approach to crop growing conditions. Starting from the mathematical representation given
by single-root models (Gardner, 1960), an analytical expression for F is derived, using
simplified hypotheses. This expression accounts for plant attributes such as the mean root
radius, the critical leaf water potential for stomatal closure and the root length density
profile growing with the crop. Environmental factors such as soil type and atmospheric
demand also influence F. The structural influence of soil comes from the required
introduction of the bulk soil hydraulic conductivity in the single-root model. The shape
of the root length density profile is assumed to be sigmoidal and a new profile is
calculated at each value of the rooting depth. A sensitivity analysis of F to all those
factors is presented. The first general result is that F decreases as the root system
grows in depth. Differences in the shape of the root profile can be responsible for
differential water stress sensitivity in the early stages of growth. Yet, low critical
leaf water potential can compensate partially for a poor root profile. Conversely, F is
relatively insensitive to the average root radius. F sensitivity to soil type seems
somewhat artificial: given the bulk soil hydraulic conductivity formula, the soil
sensitivity results from F being expressed as a fraction of the maximal available soil
water content. The atmospheric demand together with the rooting depth appear as the most
important factors. However, when assuming predictable climatic and crop evolution,
compensation occurs between those two effects leading to a relative stability of F when
the crop is fully developed. Though relying on well-known physical laws, the present
approach remains in the framework of single layer models with the same limitations. |
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