Understanding soil is vital for good agricultural outcomes and sustainable land use management, but methods for mapping and monitoring typically require manual intervention. Satellite-derived top-soil indices do not, and are therefore offer an attractive alternative – or addition – to other data gathering methods.
Two of the most common soil mapping techniques are soil sampling and electromagnetic (EM) mapping, each of which has its benefits, and when used together form a rich, calibrated data set. Soil sampling involves physical measurements using cores of soil extracted from a field/paddock and returns analysis at all depths of the sample. However, it is limited to specific locations and requires time for the sample to be processed and data to be returned. EM mapping has the benefit of creating multiple maps (e.g. texture, moisture, salinity) at different depths and is often ground-truthed against soil samples, but it is also time-consuming, and maps are not produced instantly.
Optical satellites cannot measure depth, unlike soil sampling and EM mapping, but they can provide accurate, relative measures of exposed top-soils at very large scales at a fraction of the cost of the other methods, and within minutes of satellite imagery being available (which is typically every 3 to 5 days for most of the world). In between growing seasons, the use of soil indices produced by processing satellite imagery has been demonstrated to deliver a range of time and cost-saving benefits without the need for soil sampling or EM mapping.
In the example below, the yield map generated at harvest is compared to one of several top-soil indices available from D-CAT (at 10m resolution). The strong correlation between areas with lower amounts of clay minerals and higher yielding parts of the field/paddock are immediately evident to the eye.
Another example of using soil indices as a decision aid is through managing plant toxicity issues. In the images below, plant tissue testing was performed on a crop which was exhibiting some areas of poor growth, as seen on the left-hand image which is a relative measure of canopy from D-CAT satellite processing. The image on the right is the soil index which gives a relative measure of iron bearing minerals in the top-soil, generated prior to sowing.
The low growth areas (red in the left-hand image above) directly relate to the areas where plant tissue testing returned “High” at 180 ppm and tests in the blue/green regions of the left-hand image returned “Normal” at 113 ppm. Prior to sowing, had this knowledge been available, appropriate interventions could have been made and toxicity problems avoided.
Top-soil indices have also been used to explain pH issues, such as acidity in soils, with the example below highlighting poor vegetation health of a crop (purple and yellow areas in D-CAT’s crop health image). The image was used to guide the locations of pH samples. The large patch of purple in the top right-hand corner of the image was found to have acidity (pH 4) whilst orange areas had an average pH of 6 (only slightly acidic and not problematic for the crop).
Soil indices therefore offer key decision support information to agriculture, some examples of which have been shared here. Any industry requiring knowledge of soils, such as utilities, infrastructure and construction will also gain from their use as well. Often, a time-series analysis of soil indices will provide further insights into changing conditions on the ground, and additional intelligent processing can automatically alert issues before they are visible to the human eye.
By using this service clients:
From determining whether an area of land is better suited for arable or pastoral farming, to deciding the most suitable crop to cultivate, soil indices give farmers essential information to best manage their land and crops.
D-CAT offers three different soil indices which are proven and ready to use worldwide. Whether for agricultural production applications, or as part of your sustainability plan, they have a part to play and real value to add. Please get in touch if you would like to order a one-off map or a regular monitoring service, or require any further information.