SVERIGES LANTBRUKSUNIVERSITET - Epsilon Open Archive - SLU

Tuomo Karvonen
University of Helsinki
Department of Plant Husbandry
00710 Helsinki, Finland
COMPUTATION OF CROP WATER BALANCE:
MICROCOMPUTER BASED PROGRAMS FOR TEACHING AND RESEARCH
I n t r o d u c t i o n
There is almost a continuous - during the day time - flow
of water from the soil to the roots of the plants and from
the roots through the stem to leaves and through stomatas to
the atmosphere. Flow of water in this Soil-Plant-Atmosphere­
Continuum (SPAC) is driven by the difference in potential
between soil and plant and plant and atmosphere. Generally
there exist a decreasing potential from the soil to the
atmosphere (see Fig. l) and flow rate is affected by resis­
tances in various parts of the pathway. The primary goal of
this paper is to briefly present simulation programs that can
be used to analyze the relationship between the water balance
of plant and soil and the resistances of this pathway. The
most important resistance affected by plant water potential
is stornatal resistance and soil water potential has inf1uence
on the resistance between soil and root.
C02-assimilation is closely related to leaf transpiration
rate through the simultaneous flow of water vapour through
the stomata to the atmosphere and C02-flow from the atmos­
phere to the leaf. On the other hand, leaf transpiration is
affected by leaf water and heat balance which in this way
have influence on the net photosynthesis rate. The water
status of the leaf has a pronounced effect on the stornatal
conductance of the leaf.
The simulation models have been developed with three
primary objectives in mind. Firstly, the models will be used
in teaching the very complex chain where water is moved fröm
the soil to the atmosphere, and at the same time, C02 is
diffused through the stomata to the leaf. Secondly, the
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