Page 43 - soil-plant-water relationship and water requirement
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SOIL-PLANT-WATER RELATIONSHIP AND WATER REQUIREMENT
4.2 CRITICAL GROWTH PERIODS MANAGEMENT
Plants require sufficient water throughout the growing season for optimal yield and
water saving. This is particularly important during critical stages of growth and
development.
During one or more critical growth periods during the growing season, most crops are
affected by water stress. Moisture stress during a critical phase could result in an
irreparable loss of production or product quality. Critical periods must be addressed
with caution because they are dependent on plant species as well as diversity.
To determine the demand for irrigation, an onsite evaluation of the soil for water
content, or any irrigation scheduling approach for which fundamental data has been
obtained, should be used.
Using solely plant appearance as a sign of moisture deficiency might lead to
misinterpretation, resulting in lower yield and product quality. If the plant looks to be
dry, it may already be suffering from moisture stress. During instances of significant
evapotranspiration, some plants will briefly wilt to retain moisture.
4.3 IRRIGATION RELATED MANAGEMENT
While deciding when to irrigate a certain crop, a Management Allowable Depletion
(MAD) of the available soil water should be chosen.
MAD is defined as the percentage of the available soil water that can be depleted
between irrigations without serious plant moisture stress. MAD is expressed as:
a percentage of the total Available Water Content (AWC) the soil will hold in
the root zone, • a soil-water deficit (SWD) in inches, or
an allowable soil-water tension level.
Different crops can sustain different levels of soil-water depletion at different stages of
growth without becoming moisture stressed. Some crops have critical growth periods
that last for only one stage of development, whereas others have critical growth periods
that last for several stages.
MAD should be evaluated according to crop needs, and, if needed, adjusted during the
growing season.
Values of MAD, during the growing season are typically
25 to 40 percent for high value, shallow rooted crops;
50 percent for deep rooted crops; and
60 to 65 percent for low value deep rooted crops.
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