Cation exchange capacity
Cation exchange capacity is
the first characteristic you should consider when you get your soil
test results. Cation exchange capacity (CEC for short) is
closely tied to the amount of organic matter and clay you have in
your soil since both provide spots for positively charged ions ---
cations --- to cling to the soil. In contrast, sandy soil without
much organic matter will allow
nutrients to leach away during heavy rains.
You're throwing away your money if you add soil supplements to raise
your calcium, magnesium, or potassium levels without first increasing
your CEC so that these essential nutrients will be held in place.
I've highlighted the one non-garden spot I sampled --- our chicken pasture, which was basically a lawn until we started letting chickens graze there this spring. I also sampled some of my Mom's soil, which has been intensively gardened for decades. Finally, the white columns are four different parts of my own vegetable garden. By comparing these three areas, you can see:
Most organic gardeners believe you can't have too much organic matter in your soil, but soil scientists will roll their eyes at that statement and now I understand why. If your CEC is low but your organic matter levels are high, that means you're doing something wrong and your organic matter isn't being broken down into a stable humus. Maybe you've added too much high carbon material all at once (for example, tilling wood chips into the soil) or have sprayed pesticides that killed off your soil microorganisms. That's why I recommend using CEC rather than organic matter as the most important "grade" on your holistic gardening "report card." As far as I can tell, with CEC, more is always better.
Our chicken waterer never spills or fills with poop.
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