Em4885 irrigation management practices to protect ground water

4 CHAPTER
Figure 4-9 is an example graph of a series of tensiometer measurements in a trickle
irrigated orchard. When the trend of measurements started at the begining of July,
indicating that the soil was drying out, the number of operating hours per week was
increased. After the increase, the measurements dropped again to a stable and
satisfactory level.
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FIGURE 4-9. Example graph of tensiometer readings used to guide irrigations
3. Measurements of plant water tension - using the leaf pressure chamber. The pressure
chamber is a direct measurement of stress on a plant and thus, useful in deciding
when to irrigate. But, there must be some relationship established, or another
technique in use, to indicate the soil water depletion, which is the “how much
to irrigate.”
4. Measurement of a surrogate for plant stress - a common technique would be infrared
thermometry which measures the difference between plant leaf temperature and air
temperature. A calculated “Crop Water Stress Indicator” will indicate the level of
stress on a plant and thus, can be used to decide when to irrigate. But, there must
be some relationship established, or another technique in use, to indicate the soil
water depletion, which is the “how much to irrigate.”
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