Life in the Soil

I've been nibbling away at Life in the Soil:  A Guide for Naturalists and Gardeners, by James B. Nardi, for about 2 months now.  It was easy to read, but a lot to digest, I guess.  Much of it was essentially a list of the types of organisms that live in the soil, discussing each group's place in the life cycle/food web of the community there.  I've underlined copiously, so that I can flip through for quick tidbits when I return for information or for refreshment.
Probably the overarching lesson that I took away from this book is how alive the soil really is.  The complexity and diversity of life there is phenomenal, although we (as humans) see and understand relatively little of it.

If we can't see it, it isn't important, right?  Wrong. In fact, that's the kind of thinking that leads to dead soil and, ultimately, desertification and a dying world.  Many of the discussions on soil organisms had a summary list for each group, with a category labeled, "Impact on Garden".  The options for that category appeared to be "allies", "absent", or "adversaries", or a combination of those responses.  Allies vastly outweighed either the organisms with no impact or the ones considered adversaries.  Occasionally a group (e.g. nematodes) would earn the title, "allies/adversaries" when their impact could swing different directions, or when the different members of the group had very different places in the soil community.  Nematodes, for example again, consist of approximately 15,000 species.  It's amazingly simplistic to think that "nematodes", as a group, would ONLY function as allies or adversaries in the garden.

(An aside:  why do we always classify everything as "good" or "bad" based on how it relates, specifically, to us?  Maybe we ought to grow up a little and start realizing that we aren't, actually, the center of the universe.)

I learned a myriad of things from this book.  For starters, fungi and roots literally are intertwined, each feeding the other, each in the other's space, but both "...always respecting each other's integrity." (p. 15)  Fungi finds and transports minerals and water into the roots, roots feed the fungi with sugars from photosynthesis.  It's been shown that pine seedlings with mycorrhizae absorb more than twice as much phosphorus (as well as more nitrogen and potassium) than pine seedlings without mycorhhizea.

On a prairie, typically more than 3 times as many roots are produced as shoots.  There is literally more than 3 times as much life BELOW the soil surface as above it.

"Roots mine the mineral resources of the soil, and roots make these 18 essential nutrients available to animals of the land.  In going from soil to plant, calcium, for example, is first concentrated eightfold; and in going from plant to animal, this elements is then concentrated five-fold more, for a total of 40 times the concentration found in soil  Animals are not only entirely dependent on energy that is ultimately derived from sugars produced by plants during photosynthesis, but also almost entirely dependent on plant roots for concentrating from the soil the many mineral nutrients that sustain their lives."  p.20.

I'll leave you with one other interesting interaction of soil animals....

Dung beetles recycle animal droppings, especially droppings from herbivores like elephants or bison or cattle.  Both the adult and larval stages of dung beetles rely on dung for food:  the adults eat the dung juices and then move dung underground where they lay their eggs upon it.  The dung beetle larvae then utilize it as their food source while growing.  Fly maggots also like animal droppings as both adult and larval food, and there is a frequent tussle going on over which type of insect will get most of the energy from this important food source.  Dung beetles (and rove beetles and hister beetles, two other types of beetles that commonly feed on animal dung and its inhabitants) carry tiny mites on them - up to 30 mites/beetle.  When the beetle alights on a dung pile, the mites jump off and eat fly eggs and newly hatched fly maggots, then jump back onto the beetle(s) to move on to the next food source.  Without the hitchhiking mites eating the fly eggs and small maggots, the beetles can't effectively compete with the flies to get the amount of dung that they need to survive and reproduce.

Gross?  Yes, to us.  But fascinating, too.  And a perfect example of nothing going to waste.

I would highly recommend reading this book to anyone who is interested in what's going on around them, especially gardeners.  It'll help you understand the importance and complexity of a garden's soil in ways you never even thought about before!  What connections will it make for you?

The Worms Crawl In, The Worms Crawl Out....

It seems like I'm seeing worm castings everywhere I go these days, like these I photographed this morning on the trail in the Back Five.

The castings started appearing earlier in the year than I expected - I started seeing them weeks ago - and they are more granular than I thought they should be.  In fact, at first I wondered if these little piles of dirt were actually worm castings at all.

I've recently been reading Life in the Soil:  A Guide for Naturalists and Gardeners, by James B. Nardi, and I found the section on worms fascinating.  Did you realize that the earthworms we see in our gardens are not native to North America but were brought here from "The Old World"?  There are native earthworms, but these are smaller and exist mainly where there is undisturbed native vegetation.    The native earthworms work at a more "measured pace" than introduced earthworms, a pace that better matches the actual accumulation of detritus in North American forests.  Because of this difference in the activity levels of native compared to introduced species, introduced earthworms have been found to be actually depleting the leaf litter (and thus the animals and plants associated with it) in many of the North America's forests.

According to Life in the Soil, identifying different earthworm species involves characteristics such as the number of segments between the clitellum and the head of the earthworm, the number of segments the clitellum takes up, and the shape of the first head segment.  No, I haven't attempted this yet!  (But I probably will, if I can find a decent guide....)

Earthworms will dig as deep as 10 feet, and they literally eat the soil as they push their way through it.  The resulting manure - the earthworm's castings - is both less acidic and richer than the soil the earthworm took in.  Calcium carbonate has been secreted into the material by glands along the earthworm's gut, and the resultant castings therefore have about 50% more available nitrogen, phosphorous, potassium and calcium than the surrounding soil.

Earthworms move a surprising amount of soil.  Nardi reports that Darwin's last book was about earthworms, and that Darwin estimated that earthworms produced about 40 tons of castings/acre/year on the soil surface in Britain.  He also estimated that this activity would cause objects to be buried at a rate of 0.1"/year simply by the actions of earthworms!

I guess the earth really is moving under our feet when there are plenty of earthworms in it!