Not sure why this is, but I find the biggest nightcrawlers in my garden, in the top several inches of clay. I have a relatively small backyard in Oregon's Tualatin valley where we have a clay silt soil. We get a lot of rain, about 40-50 inches a year, but essentially none between mid-June until mid-September. I have 2-3 foot wide planting strips in the garden, where we removed about 30% of the clay in the top 16-18 inches, and worked in sand and compost. There are clumps of clay in this zone. When I dig in the strip, almost all the worms are in the clumps of clay, and especially in clay at the bottom of worked section.
My hypothesis: that nutrients from the compost are washing down and being absorbed at the clay surfaces, which seems to promote fungus growth at the clay boundary. The very large earthworms in my garden seem to be eating this fungus or microorganisms on the wet clay surface. If I break apart a six inch clump of clay, I invariably find several large fat nightcrawlers in the clump.
Seems that when I add cardboard, or other moisture retaining materials, I find the earthworms there as well.
I wonder if I add biochar pieces, would I find earthworms next to the biochar surface?
Of course for this to work, there needs to be a constant supply of composting materials above these earthworm feeding zones. Is this perhaps why Amazonian people used Loma Preta biochar + composting systems?
