Campbell Scientific Sentek EasyAG Installation Guide v 3.0 User Manual

Page 7

Site Selection

Page 4

Crop water use is governed by many factors such as soil properties, crop stage, water quality, weather
patterns and type of irrigation system. These factors need to be considered when defining the macro zones
on your property and are described in the following pages.

Micro zone selection determines the position of access tubes in relation to the crop and irrigation system.

Micro zone selection considers the:

• Areas of root zone and canopy spread
• Water distribution uniformity (sprinkler pattern)
• Moisture pattern of drip irrigation
• Surface, topographic and soil anomalies

The consideration of these factors will help you find the best representative position or site for probe
placement within the macro and micro zones.

Macro and micro zone selection is described in greater detail in the following pages. If you require further
information, consult your Sentek reseller and/or a trained agronomist.

Important factors you should know that affect crop water use

All the factors listed below can have an impact on the way the water is stored in the soil and on the way that
plants use that water. They affect transpiration and evaporation rates and have a direct impact on irrigation
scheduling. In macro zone selection, it is important to consider the way these factors influence water use in
a particular area or zone:

• Climate
• Soils
• Crop
• Cultural

management

• Irrigation

system

Climate

The most commonly recognized factor in influencing the amount of crop transpiration is the weather.

Temperature

Crops need to draw up water to compensate for water use through transpiration (water loss through the
leaves) and evaporation (water loss from the surface of soil and leaves). The demand increases with
increasing temperature up to a maximum threshold for each crop (when the stomata close and
photosynthesis stops).

Humidity

Atmospheric demand for transpiration and evaporation is relative to the humidity (amount of water vapour in
the air). The higher the humidity level, the lower the demand.

Wind speed

Crop transpiration and evaporation increase with increasing wind speed, creating an increased water
demand. At higher wind speeds, transpiration eventually decreases due to stomata closure, but evaporation
increases.

Solar radiation

On sunny days, crops can synthesize more basic sugars and more complex plant food compounds, through
the combination of atmospheric carbon dioxide and soil-derived water, than on cloudy days. Although crops
vary in their sensitivity of photosynthetic response, they all require access to greater amounts of soil water.