Soil color is one of those things you can just look at and it will teach you so much. It tells you about organic matter. It tells you about drainage. It tells you about how iron behave in the ground. In short, you get a quick read on soil’s history. And it’s not just a read of your mind but a read we share with each other.
It is a subjective impression translated to a repeatable notation. Anyone can verify it later. The Munsell system do that. It’s a kind of short code for notation. First, there’s hue, which are the color family. Second, there’s value (light to dark in soil). Third, there’s chroma (how strong or muted that color is).
Why Soil Color Matters
Low chroma and low value would be a dark topsoil. Higher chroma and a redder hue would be a bright red subsoil. Once you grasp those elements the system no longer seem abstract. It’s shorthand for what you’d notice yourself when digging.
That’s where the shorthand gets important if you’re moving down a profile. Upper layers may get darker from the accumulation of organic matter. Deeper down, it shifts to colors based off iron and other minerals. In well-drained places, it’s usually gradual. In poorly drained ones, you begin to notice olive or even grey tone.
That’s because standing water there has chemicaly reduced iron. Within inches of one another, the same soil may be gray and red. That occurs where the water table go up and down during the year. It’s like a sort of mineral-written diary.
Common color families is laid out in the infographic above. Yellow-brown hues dominate many temperate croplands. These develop through moderate levels of oxidation. Where there’s more red, that means iron has aged into hematite. This happens when warmer drier seasonal conditions exist. Areas where water tends to linger are marked by yellows and olives. The reason? Oxidation is slowed down in those areas.
On their own, none of these hues suggests one specific type of crop. But they do narrow the list of what’s most likely to succeed with little or no added effort.
“Repeatable behavior will help you read color in the field. Tear off a fresh chip from the surface of soil. If it is dry, lightly moisten it. Examine chips under an unfiltered exposure (neither shaded nor direct sunlight). Record both the moist and dry readings. Both may vary sufficiently to alter your classification of the horizon. A spot of earth may appear darker by as much as one value when wet. So, neither should of be omitted in a full description.
They are used for more than that. These reading are read by farmers. Dark on the surface flags spots to protect from erosion. Improves its structure (organic matter). And better holds nutrients. Subsurface greys prompt another look at drainage. Check first here if you plan to plant something precious that doesn’t like to have wet feet. High light-colored readings in dry zones may signal an accumulation of lime. This affects phosphorus availability.
Every reading prompts a practical question: What will it grow without a lot of help? Observers’ squabbles is diminished by it, too. “Brownish” is a perfectly acceptable descriptor of a horizon, and yet two individual may be describing something entirely different until one of them writes it down in that three-part notation. That common denominator helps when data travel from season to season. This happens when one consultant compares notes with another over a large region.
Remember color does not replace chemical tests or texture. But it does provide the quickest starting map. Knowing the main colors help put the rest of the profile description in place faster. Note the way those colors shift with depth. Treating every reading as a start to a question is where it gets realy interesting. Don’t make it the end-all, be-all.