Soil Life and Your Garden- Something to Consider

 I was trying to think of  catchy, attention grabbing title for this post.  I had something like Microscopic entities grow Giant Kale!  with "and, lettuce and broccoli and sweat peas......" heading up the text.  I went with a much 'quieter' heading, but as Sci-Fi fantastic as it sounds, those kale growing micro-organisms are as real as you and I.

As spring approaches and we start planning and preparing our vegetable gardens, it's a great idea to take some time to learn about the life within the soil.  I've read that a double handful of good garden soil contains more living organisms than there are people on earth.  It's true.  With billions of bacteria, countless yards of fungal hyphae (threads), hundreds of protozoa, dozens of nematodes, and don't forget the earthworms, arthropods, and gastropods there's a lot going on down there!  Sound scary?  It shouldn't be.  Healthy garden soil has a work force of microbes (microscopic organisms) that provide food, water, pest and disease protection, and nicely aerated soil for your plants.  There are certainly 'bad guys' in the soil- bacteria, fungi and nematodes to name a few- that are out to eat your plants. The idea is to foster a large and diverse population of soil life to keep the harmful organisms in check. 
Over millions of years plants have evolved intricate relationships with bacteria, archaea, and fungi in the soil.  In nature, plants actually expend some of the energy from photosynthesis to create "exudates." These excretions from the plant roots contain carbohydrates, proteins and minerals specifically aimed at attracting bacteria and fungi into the area within their root system.  That may seem crazy at first, but these organisms are responsible for 'fixing' nitrogen so it is in a form available to the plants, as well as searching out, unlocking and transporting critical phosphorus, water and other nutrients. One of the most well known examples of bacteria and plant symbiosis is with legumes.  Plants like clover, sweat peas,  beans, and vetch are great companion plants and cover crops because they add nitrogen to the soil.  However it is actually different species of Rhizobia bacteria that will 'infect' the plants root tissue and then from inside the roots convert nitrogen to an available form for the plant to use.  In exchange the bacteria gets carbon and air from the plant.
If we're talking vegetables a few things to remember: They rely on different types of bacteria working "together" to provide nitrogen in the Nitrate form they prefer.  You may know that vegetables prefer a pH of 7 or just below.  What you may not know is that these beneficial bacteria also prefer a pH of 7, and without disruptive influences from us, the protective film bacteria create around themselves will slowly raise the pH of the area around them to 7 to help their numbers grow.  Other plants like trees and shrubs tend to prefer somewhat more acidic soils and have built relationships with fungi who also want more acidic soil and create acids themselves that will lower the pH of nearby soil!
Bacteria are also the main food stuffs of earthworms.  Earthworms may eat soil and organic matter, but what they are really after are the bacteria attached to those particles.  It is then up to other bacteria in the gut of the earthworm to process what they have ingested.  The earthworm waste, or "castings" created by this process are considerably higher in nitrogen and other critical nutrients than the matter they'd consumed.
Growing organically, adding compost, properly made compost teas and organic matter to your soils, mulching with shredded leaves, green mulches and shredded pine bark for the veggie garden are all great steps to take in support of healthy soils.
This is a huge topic, with books written on every different type of participant in the 'Soil Food Web'.

I love learning and talking about this stuff! In  my classes it so great to see people be as surprised and amazed as I first was to realize just how much life is in the the soil, and just how much the plants depend upon that life. 
Want to learn more on your own?  A lovely resource is the book Life in the Soil by James Nardi. An education and guide is also provided by the book Teaming with Microbes: The Organic Gardeners Guide to the Soil Food Web.   You can also check out the USDA-NRCS page on soil biology by Elaine Ingham.  There you'll find some very sciency talk and lots of great electron microscope images. Or if you are really getting into it, how about the website for The American Society for Microbiology?