The UN has declared 2015 as the International Year of Soils. What is soil? Well, it’s simple – minerals derived from weathered rocks; and organic materials derived from living and dead organisms. Soil is also complex – it’s the “skin of the earth” that supports all forms of terrestrial life, including our homes, our food and our oxygen-giving plants.
Indeed, soil is the most diverse eco-system on the planet – a teaspoon of soil can potentially provide habitat for thousands of bacterial species, fungi, protozoa, nematodes and more. The soil food web is very complex and plays a major role in contributing to the health of soil and its ability to support our food systems.
The importance of soil is the theme of Ag Day 2015, scheduled for March 18 on the west side of the State Capitol. This year’s event will feature information about our farmers’ and ranchers’ efforts to preserve, restore and protect the health of this essential resource.
When soil scientists studies soil, they examine the soil profile. A soil profile is the vertical arrangement of different layers of soil – known as soil horizons. Soil horizons can give us a lot of valuable information by providing evidence for different geological, hydrological, biological and climate-related process that occurred in the earth’s history that led to the formation of a particular soil in a specific region.
O horizon: This layer is generally present on top and the “O” stands for organic matter.
A horizon: The A horizon is the topmost mineral horizon and generally contains partially decomposed organic matter which gives the soil a color darker than that of the lower horizons.
B horizon: This layer forms underneath O and A horizons and has undergone many changes. Typically, this layer has accumulation of materials such as clays and iron oxides that have slowly leached from layers lying above them.
C horizon: The C horizon is composed of is the unconsolidated material underlying A and B horizons, typically formed from the bedrock that has weathered and broken to smaller particles.
A fun way to look at this would be a soil profile cake – an edible cake that resembles the various layers of soil. Here’s how you might achieve that:
O Horizon: Crumbled up dark chocolate cake, mixed up with pistachios to look like “leaf litter” and “earthworms” made of agar jelly.
A Horizon: Dark chocolate cake to represent organic matter that gives it a darker color.
B Horizon: Fudgy, sticky chocolate brownie layer to represent clay accumulation (clay minerals often feel sticky and slippery to touch).
C Horizon: A thin layer of chocolate-vanilla marbled cake with chunks of almonds, cashews and walnuts to represent unconsolidated rock material.
To hold all the layers together, you can use whipped cream and chocolate ganache – which peek out of the “soil profile” to represent while calcium carbonate deposits (often seen in arid soils) and preferential flow paths of soil water.
If you’re wondering if a soil cake looks good, well, check out the pictures:
It looks mighty tasty to us! There’s some competition for mud pie!
Thank you to CDFA environmental scientist Geetika Joshi, Ph.D. for the concept and for baking the soil cake.