Soils define the transition zone between the rocks that make up the Earth's crust (lithosphere) and the environment where living organisms coexist (biosphere) with the gaseous layer surrounding the Earth (atmosphere). They are defined as the dynamic and porous layer composed of minerals, gases, and organic matter from living beings that inhabit the Earth's surface. Furthermore, they are the space that completes the life cycle, where we can find its "end" and "beginning." This is why there is the famous saying, "From the soil we come and to the soil we return to be reborn."
The scientific field dedicated to the study of soils is called edaphology or "pedology." Soils are a natural entity; some consider them living entities due to the great variety of organisms and plant life they harbor. They constitute a storage site for water, carbon, and nutrients that allow plant growth. The most fertile soils are those with the greatest ability to support plant growth through the availability of nutrients. Nutrients are all those elements that are essential for optimal plant growth. Some examples include nitrogen, phosphorus, potassium, magnesium, calcium, iron, and sulfur, among others. Roots participate in soil aggregation and structuring, protect them from erosion, and create porous spaces that allow water infiltration. The greater the number of roots, the more protected the soil is because the network covering it is larger.
The structure, texture, mineralogy, water content, and chemical composition of soils exert significant control over the distribution of organisms. For this reason, the determining factors in soil formation include climate, parent rock (underlying rock), biological activities and organisms present in the area, topography, and time.
If we were to cut a cross-section of the soil from the surface down to the bedrock, we would observe the layers that make up the soil profile. These layers are called horizons, and they are formed by the vertical movement of water, minerals, biological activity, chemical processes, and organic matter. They are clearly distinguishable layers located from the bottom to the Earth's surface. Examples of the nomenclature used for horizons (from the surface to greater depths) are: O, A, E, B, C, R.
There are different systems for classifying soils. The Russian school, a precursor to soil science, classifies soils based on their formation processes. The system used in the United States (and Puerto Rico) divides them into 12 major orders, 64 suborders, 300 groups, 1,200 subgroups, 6,000 families, and thousands of series. This system forms a large taxonomy where orders constitute the largest and most general groups, and series are the most specific classifications. This system is based on soil structure, texture, chemical properties, and profile for classification.
In Puerto Rico, nine (9) of the eleven (11) soil orders, 29 suborders, and 164 series are observed. The predominant soil orders in Puerto Rico are Inceptisols (37%), Ultisols (27%), and Mollisols (21%). In our archipelago, 28% of the soils are suitable for agriculture, although the spread of urban development poses a clear threat to our food security.
The agency responsible for updating and distributing this information in digital format is the Natural Resources Conservation Service (NRCS).
The map of the San Juan Bay Estuary basin shows 8 soil orders, of which Entisols (12.8%), Ultisols (7.5%) and Inceptisols (6.1%) predominate.
