Soil Available Water

This article will explain the difference between available water capacity (AWC) and readily available water (RAW)

Fabio Mangia avatar
Written by Fabio Mangia
Updated over a week ago

This article comprise one of a series of articles with technical content to help you to understand how our products works. This refers to the Irrigation Management product, Agrosmart Aqua. You can find below a list of other articles of this series regarding irrigation management:

Soil available water

The soil available water capacity (AWC) is the total water content that soil can store up to a certain depth. This depth corresponds to the effective root system (soil layer where most of the absorbent roots are concentrated). For this reason, if the roots grow, AWC increases accordingly. Thus, AWC represents the range of moisture available for plant roots.

However, the difficulty for the plant to extract water varies according to the amount of water in the soil. The lower the percentage of water in the soil, the greater the difficulty in extracting water. The fraction of water in the soil that can be easily removed by the roots is called Readily Available Water (RAW). When the RAW runs out, the plant needs to make a greater effort to extract water, generating stress. Since RAW is a fraction of AWC, it will increase as AWC increases.

Thus, when RAW runs out, the critical humidity is reached, which is the limit to start irrigation without leaving the plants under stress. Therefore, to obtain water savings, the ideal is to always replace the water in the soil when the RAW runs out.

Soil humidity points and the relation with available water for the plant. Adapted by Farsad’s (2016).

FARSAD’S, A. Soil-Water Status: Saturation, Field Capacity and Wilting point. 2016.

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