Case Studies

SoilOptix® Custom Layers: What is Loam, Leakability & Plant Available Water?

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By: Zachary Harmer B.Sc.; SoilOptix Inc.

As part of the SoilOptix® technology deliverable, soil texture layers are provided. This includes percentage of Clay, Sand and Silt (Figure 1). Additional layers may be derived from these properties however, which includes Loam (%), Leakability and Plant Available Water. 

SoilOptix® Clay Layer
SoilOptix® Sand Layer
SoilOptix® Silt Layer

Figure 1: SoilOptix® layers: Percent of Clay, Sand & Silt


SoilOptix® determines the Loam layer through a simple addition of Clay + Silt. Its units continue through and is represented as a percentage. An example of this map is shown below in Figure 2.

SoilOptix® Loam layer

Figure 2: SoilOptix® Loam Layer

Leakability & Plant Available Water

These two custom layers involve Organic Matter, Clay and Silt and act as index layers (i.e. unitless). Leakability is an index of the potential for water to move through a given soil and acts as an inverse to Plant Available Water. The lower Leakability value, results in more likely water to leach through the soil, relative to other parts of the field. As an example, sand fields can have very low values for Leakability, resulting in the high movement of water in that soil.

Alternatively, Plant Available Water acts as a basic water retention model, where as PAWater increases these areas will hold more water. It is possible for this value to go over 100, indicating higher clay content and higher organic matter levels.

An example of each of these layers is shown below in Figure 3.

SoilOptix® Leakability Layer
SoilOptix® Plant Available Water (PAW) Layer

Figure 3: SoilOptix® Leakability & Plant Available Water Layers

The differences across various levels of Leakability and Plant Available Water are based on ranges of Organic Matter, and texture. The table below illustrates how these changes affect the index values of these custom properties.

Low OM1Low Silt/Clay9055813
Low OM1Medium Silt/Clay6020202343
Low OM1High Silt/Clay1045454893
Low OM1High Silt/Low Clay5905898
Low OM1Low Silt/High Clay55909398
Medium OM3Low Silt/Clay90551419
Medium OM3Medium Silt/Clay6020202949
Medium OM3High Silt/Clay1045455499
Medium OM3High Silt/Low Clay590514104
Medium OM3Low Silt/High Clay559099104
High OM10Low Silt/Clay90553540
High OM10Medium Silt/Clay6020205070
High OM10High Silt/Clay10454575120
High OM10High Silt/Low Clay590535125
High OM10Low Silt/High Clay5590120125
Table 1: Expected Leakability and Plant Available Water ranges based on various OM and Texture levels.


These custom properties further extend the possibilities of the textural and physical properties which are reported from standard lab procedures. The utilization of these properties extends to the knowledge of the user; however, applications may include variable rate seeding scripts, irrigation management or combining with other precision agriculture datasets (e.g. normalized yield data).