Soils lab is fun!

This is a picture I took of someone testing a soil sample with hydrochloric acid to see if there is a fizzing reaction. If there was we would note it as a presence of Calcium Carbonate (CaCO3).

CaCO3 is important in a soils profile. This compound's source of Calcium comes from the parent material of the soil, the bedrock so to speak. As it weathers as a result of chemical or physical processes, the calcium rock can be broken down into minerals or even elements. And Calcium is one of them.

The Carbonate in the compound comes from the respiration of plant roots, which are exhaling CO2 just like you and I. The carbonate mixes with the calcium to create CaCO3.

Now this compound is in fact produced close to the surface of the soil, where the roots are right? But it doesn't always stay at the surface. The compound can be carried down through the soil profile by water in a process called illuviation. This simply means the CaCO3 is getting carried in the water, by force of gravity, lower into the soil.

You test for presence of CaCO3 at different depths in the soil (using the acid test). The closer to the surface the CaCO3 is found, the less effective precipitation the soil experiences. I've seen soil with no CaCO3 in it and I've seen soil where the CaCO3 is at the very surface. Can you guess what the different soils were like?

The first one was a grassland soil with sparse, small vegetation on a south facing slope in Montana. It gets 11-13 inches of precip. per year, but since it is angled, the water runs off before it soaks into the soil, furthermore south facing slopes get more solar radiation than other aspects due to our northern latitude so the water not only runs off, but also evaporates before going into the soil.

The second soil without CaCO3 was in fact less than 100 feet from the very dry soil. It has the same amount of annual precipitation, but it is low in a gully where water collects and where it is shaded. The dominant vegetation here was snowberry, a shrub, rather than the drought tolerant species of the south facing slope. This change in topography resulted in leaching the Calcium Carbonate not only to lower depths in the soil, but lower down the slope, and eventually perhaps into a stream or groundwater system. All things are connected: topography, solar radiation, water, plant life.