Beneficial Soil Organisms
Part 4: Arthropods and Earthworms
Originally published in the Rose Garden newsletter, December, 2003.
A while back I was digging through my vermicompost pileŚwith my bare hands of course. I should tell you that my vermicompost pile is about 30 feet long, 3 feet high, and 3 feet wide and consists mostly of horse manure and grass clippings. Anyway, I was digging on the "fresh" end to see how the worms were doing and as I scooped out some manure, I came within one poop ball of scooping up a really gigantic and gross-looking bug.
Turns out potato bugs are a good thing to have in one's compost pile. They are members of the arthropod genus, a group of soil organisms whose main function is to shred large organic matter and mix it into the soil, which is exactly what my potato bug was doing crawling around in the fresh horse poop and grass clippings.
Other beneficial soil arthropods include centipedes and millipedes, sowbugs, ants, beetles, and springtails. When arthropods shred the large stuff, they increase the surface area making it more available to beneficial bacteria and fungi. Bacteria and fungi convert the nutrients into biomass and make the nutrients available to your roses on demand. Arthropods also improve soil structure when they burrow and poop. Some arthropods eat soil fungi and in doing so, they release fungal biomass nutrients and regulate the fungal population. My friend Chris Reid calls arthropods the pick-up trucks of the soil because they transport organic material and nutrients throughout the soil
A square yard of biologically active soil will contain 500 to 200,000 arthropods.
Everyone who was ever a kid knows about earthworms. I have fond memories of night crawler hunting with my grandpa. It was great fun to sneak around grandma's garden in the middle of the night with a flashlight. You must walk softly and grab the worms quick before they snap back into their holes.
There are three major types of earthworms: epigeic or surface worms, endogeic or upper soil worms, and anecic or deep-burrowing worms. Night crawlers (Lumbricus terrestris) are anecic and found mostly in the North and East. Composting redworms (Eisenia fetida) are epigeic and prefer an environment rich in organic material.
Like arthropods, all earthworms are major shredders and decomposers of chunky organic matter. Earthworms eat bacteria and fungi growing on the organic matter and thus release nutrients stored in their biomass. Interestingly, even though earthworms eat fungi and bacteria, their poop (castings) contains even more of them, particularly beneficial fungi. Also, any pathogenic organisms that go through a worm's gut are neutralized.
Earthworms dramatically change soil structure as they burrow and poop. They can turn over the top 6 inches of soil in 10 to 15 years! As the soil becomes more healthy and earthworm populations increase, they pull more and more organic matter into their burrows, helping to mix it into the soil. This mixing action improves soil structure, aggregation, and water infiltration.
Earthworms have few enemiesŚman and birds make up the list. Since birds do such good work for us in terms of above-ground pest control, we can't deny them a few worms. Man regularly reduces worm populations through tilling and the application of chemical fertilizers and pesticides. Fortunately, we organic gardeners do none of the latter and little of the former so our worms are comfy and happy.
A square yard of highly organic soil will contain more than 300 worms.
Photo from whatsthatbug.com.