One quick note: When it comes to physiological processes in plants and physical processes in soils, there are never exact cut-off points or thresholds where something like crop stress begins or soil drainage stops. While all of the concepts below are useful to describe what is happening in the crop and the soil, we must recognize that our goal is to simplify an impossibly complex system into terms and measures that we are able understand and give us something we can act on with confidence.
The point at which the soil contains as much water as it can hold without it being quickly lost to drainage. While additional water can physically still fit in the soil, it will be lost from the profile in a matter of hours instead of remaining. While there's not an exact cut-off point where water completely stops draining from the soil, it does slow down greatly at the point we consider to be Field Capacity.
Permanent Wilting Point
This is the point at which the soil holds so little water that it is impossible for plants to extract another drop, and it would take sun-drying or oven-drying the soil to remove any additional water molecules that are still present. Crops will experience some wilting long before this point, because even if water is still available to the crop it may not be able to make it from the soil to the leaves fast enough to keep up with the plant's transpiration.
Plant Available Water Capacity
The total amount of water that a soil can hold which the crop is physically able to access. It is the water in-between the Field Capacity and the Permanent Wilting Point of the soil. We often describe this amount of water in "inches or water per foot of soil" which is usually shortened to "in/ft."
Plant Available Water
This is one description of how much water is currently in the soil. We often describe this value using a percentage, comparing the current amount of water to the Plant Available Water Capacity. Since Plant Available Water is counting all of the water down to the Permanent Wilting Point, it means that we never want to allow this to get anywhere close to zero percent!
The stress point is our best estimate of when yield loss begins to occur due to insufficient water for the crop. Generally, this is when about 50 percent Plant Available Water remains in the root zone of the crop.
Readily Available Water
While Plant Available Water describes all of the water that is possible for the crop to access, (even to the point of severe stress), the Readily Available Water describes how much water is left before the crop reaches that stress point. We most often find it useful to describe this amount of water in terms of "inches or water per foot of soil" which is usually shortened to "in/ft."
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Features and Enhancements June 14 2019
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What is ServiTech Bridge?
ServiTech Bridge is the cutting-edge web application that allows growers, agronomists, (and more!), to quickly and easily get actionable recommendations from their in-field sensors, crop health imagery, and weather forecast. We don't just give you a ...