Monday, February 22, 2010

It’s a jungle out there

My previous post initiated some pondering on the amazing properties of dirt. The preferred term used by horticulturalists and biologists is "soil." The complexity of this material is astounding. To help explain why it matters whether you mulch with compost, you have to look at the microscopic level. Healthy soil supports a vast number of organisms that enhance the soil structure, recycle nutrients, and even help to control disease by processing food through their systems. These include macro-organisms such as beetles and worms, but the majority of the work is done by the tiny guys.
The ecosystem in your soil is made up of an astonishing diversity of microbes that play an important role in forming the crumbly, aerated soil structure that plants need to thrive. Fungi and bacteria produce substances that bind soil particles together. Beetles and earthworms consume soil and excrete castings that increase soil's arability. These macro-organisms also create nutrient-lined tunnels for roots, water and oxygen.
Most soil organisms get their energy from breaking down organic compounds, but there are some that get their energy from light, some from inorganic sources such as carbon dioxide, and a small but valuable group that gets energy from oxidizing inorganic compounds.
Plants need simple inorganic (non-carbon) forms of nutrients. Soil microbes create the nutrients plants need out of the raw materials available: organic and inorganic. They do this in several ways. Microbes speed up the decomposition process, during which acids are produced that chemically combine to form stabilized organic matter. Other microbes convert organic matter into plant friendly, inorganic nutrients. This is called mineralizing and nematodes, for example, can produce hundreds of pounds of ammonium per acre per day. Wow!
Bacteria also transform inorganic material into different inorganic compounds. Probably the most familiar example is nitrogen fixing bacteria that convert a type of nitrogen from the atmosphere into forms that plants can use. The roots of legumes host these beneficial bacteria as do the alder trees of the PNW. Alder trees were early colonizers after the Mt. St. Helen's eruption and the reforestation of that area has taken place faster than anyone could have predicted. A similar beneficial microbe is mycorrhizal fungi which invade a plant's roots or feed on carbon compounds exuded by roots, but repay the favor by fixing atmospheric nitrogen into a plant friendly nutrient.
Soil organisms control disease by generating substances toxic to the disease causing organism. Some beneficial predators, such as nematodes and protozoa control population levels of the harmful organisms. Some microbes simply compete with them for location or food source and win. Hurray for our side!
So, how do you encourage a jungle of diverse soil volunteers to make your garden thrive? Most soil organisms rely on organic matter for food. Compost is a readily available, ecologically friendly way to inoculate the soil with a wide diversity of organisms and provide them with a high quality food source. In addition, you can protect your volunteers by minimizing compaction, restricting pesticides and improving water drainage. So, go get your compost and start spreading!

No comments:

Post a Comment