First off, it is soil not dirt. Got that? Dirt is what you track in on your shoes, soil is a living universe of microorganisms that supports all life on this planet.
Last week I attended the pre-opening press conference for "Dig It! The Secrets of Soil" exhibit at the Smithsonian's Natural History Museum. Sounds thrilling right? While the subject is pretty *ahem* dry and musty. I did learn a few new things like just how little we know about our soils. Like air and water, we are not making more of this essential element and once we've stripped off the top soil and poisoned the layers below we are basically screwed.
An off-hand comment at the press conference led me to the NRSC web site, which I'd never heard of before and here I thought I had traveled all over the USDA's various sites! While there, I have hit the mother-lode for soil nerds. This page tells you everything you want to know about testing your soil quality yourself. True DIY. Since Maryland and DC do not offer free soil tests for their citizens, we have to take it upon ourselves to find out what toxins we have underfoot or what nutrients our soils lack. The earthworm assessment test caught my eye. Basically, you dig up a square-foot of earth than flush out the earthworms with a noxious mustard-water mix, then count them up. Of course, you rinse off the poor things before returning them back with the soil. The interpretative guide states: "About 10 earthworms per square foot of soil (100 worms/m2) is generally considered a good population in agricultural systems." And if you just read that and thought to yourself, "Huh, I wonder how many earthworms per square foot are in my yard?" Congratulations, you are a soil nerd.
The Dig It! exhibit runs until January and there are plans to have it travel across the country. Pictured here are soil samples from 54 US states and territory. No surprise to see DC, VA, MD, and DE are basically red-orange-yellow clay.