6. INTRODUCTION
6.1 Crop Water Stress Index (CWSI)
The crop water stress index (CWSI) was developed as a normalized index to quan fy stress and overcome the
e ects of other environmental parameters a ec ng the rela onship between stress, plant temperature and air
temperature.
CWSI is a very useful tools to
prevent drought and determine irriga on scheduling
. But is for instance also used
in process of plant breeding (phenotyping), where the main goal is to nd varie es and individuals that are less
sensi ve to water stress.
To dis nguish CWSI value from NDVI, which also operates in the range of 0 to 1 (or -1 to 1), we prefer to use
a percentage to express a CWSI value and
we are opera ng in percent range 0% to 100%
. Value CWSI = 0%
corresponds (ideally) to the maximum possible plant transpira on (stomata are completely open, enough water).
Value CWSI = 100% corresponds (ideally) to zero transpira on for fully enclosed plant stomata. A value between
0 and 100% determines the degree of water stress. Rising value means higher level of water stress. Assignment
of CWSI level to crop condi on see in the table below.
Colour
Water stress level
descrip on
Level of stress
Low stress
Crop is prac cally free of water stress
No correc ve ac on is required, a high yield can be expected (unless
other problems occur). In the case of water management, it is advisable to
consider whether crops are irrigated too much.
<10%
Low to medium stress
Normal levels of water stress during warmer days
- even if the plant is well supplied with water.
10% - 20%
Medium to high stress
Normal levels of water stress during warmer days
- prolonged and persistent exposure to water stress at this level can result in
reduced yields or crop damage. Reginato and Howe [
?
] found that co on yield
showed the rst signs of decline when the CWSI average during the season was
greater than 0.2*.
20% - 40%
High stress
Crop is exposed to high level of water stress. With long-term exposure to
water stress to a given extent wil ng or signi cantly reduced yield could
be expected.
40% - 80%
Extremly high stress
The yield can be expected to be very low without
correc ve measures. There is a high probability that without irriga on crops
will wilt.
>80 %
Please nd the full explana on of CWSI and WIRIS Agro features and recommenda ons in document:
Analysis of crop water stress index (CWSI) by Workswell WIRIS
This document is distributed in printed version with each WIRIS Agro unit.
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Revision 1.0.0 EN, 25
th
Oct, 2019
All pictures are only for illustra on.
Real values may vary.
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