The Biology Of Soil Health 4

At least two studies have revealed this beneficial characteristic of mycorrhiza. In one, tomato plants were warned of the presence in nearby plants of a fungal disease; in the other, bean plants were warned of attacking aphids. In both cases, non-affected plants were able to set up defenses in advance of any infestation.

Microbes consume the organic residues and incorporate some of the carbon in their bodies, with the rest released as CO2. Over time, as these microbes live, breathe, and die, much of the remaining carbon will also be released as CO2. However, some portion will be converted into more stable forms of carbon, and some will be protected in soil aggregates. These latter forms of carbon will stay in the soil much longer, adding to the soil organic matter pool. The latest scientific evidence suggests that in healthy soils more carbon is retained in these more stable forms than is the case in less healthy soils. This is probably due to the higher levels of microbial activity and greater aggregate formation in healthy soils, which usually leads to higher levels of soil organic matter.

Armillaria ostoyae, nicknamed the "Humongous Fungus", is an organism that covers 2,385 acres (almost 4 square miles) of the Malheur National Forest in Oregon.

Mycorrhizal fungi are the most common fungi in healthy agricultural soils, dominating compared to the decomposer and pathogenic varieties. They form "common mycelial networks" with their hyphae, connecting with each other both within and between species, and these networks can pass chemical messages, nutrients, water, and maybe even things that we don't yet know about.

Actually, it is the fungi that are good at breaking down the tough-to-degrade organic materials such as lignin. Most bacteria cannot degrade these substances, or do so very slowly. This is one of the main reasons that forest soils are fungal dominated.

Sand is defined as particles between 0.5 and 2 millimetres (mm) in size; silt is between 0.002 and 0.5 mm; and clay particles are very tiny -- smaller than 0.002 mm and down to the size of a bacterium -- less than 0.001 mm (one thousandth of a millimetre).

Farm fields are often bacterial dominated, mainly because of the management practices used (tillage, in particular, is hard on fungus). When soil health best-management practices are adopted (e.g., no-till, cover crops), the ratio eventually changes as fungal populations become better established. These types of farm fields more closely mimic mid-successional ecosystems such as grasslands. Several benefits arise from this change: for instance, higher fungal populations are closely associated with higher organic matter levels and better soil aggregation.

1 Plants put out root exudates to attract and grow beneficial microbes in their root zone. Some of these microbes help plants to prevent and/or fight disease organisms. 2 Some fungi can trap nematodes in hyphal loops; they then gradually consume the nematode (which are often root feeders). 3 Protozoa eat bacteria and some organic matter, but not living roots. 4 Some types of nematodes are root feeders and they can cause a lot of economic damage in crops.

1 - summer fallow (ploughing, followed by leaving the field bare) is usually done to destroy weeds and conserve moisture, but in fact it starves the soil food web (no residues or plant root exudates), reducing its size and diversity. 2 - adding perennial pasture to a rotation (putting some portion of a farm into pasture for a few years, before returning it to production) increases the inherent fertility (and optimizes the soil biology) due to the organic matter -- residues and exudates -- added to the soil over the pasture period. If animals are grazed obn the pasture, they will also fertilize the soil with their manure; 3 - regular tillage destroys soil structure and results in bacterial dominated fields. 4 - cover crops add carbon, retain nutrients, and protect and feed the soil food web.

The primary productivity of an ecosystem is the amount of solar energy that the system converts into biochemical energy, for any given period of time (usually expressed as an annual figure). The word "net" means that the amount of that energy used up by the organisms in the ecosystem over that time (the energy they use to live) has been subtracted. This can be thought of as the gain in biomass over that period, as the biomass represents the stored energy.

"Recalcitrant" refers to the ability of an organic substance to resist degradation by microbes. For instance, fresh plant residues are not at all recalcitrant, whereas biochar (organic materials heated in the absence of oxygen, so that almost all of the non-carbon materials are driven off and only black carbon remains) is usually extremely recalcitrant. This means that decomposer organisms are not able to break it down further and release the carbon back into the atmosphere as CO2. Extremely recalcitrant substances can remain in soils for thousands of years.

Nutrient release from minerals can be accomplished by certain enzymes, but these enzymes are produced by plants and some microbes, rather than by earthworms.

Yeast is classified as a fungus, even though it is single-celled (the cell has a nucleus and organization and is therefore eukaryotic, as are all fungi); mites are among the tiniest soil arthropods; amoebae are among the largest soil-based protozoans; and algae are plants, which can photosynthesize, even though many varieties of algae are single-celled (but like all plants, also eukaryotic).

1 - SOM is about 58-60% carbon, on average; 2 - one tonne of soil C equals about 3.67 tonnes of CO2; this is because you have to add the weight of the twon oxygen atoms (O2) to the carbon atom (C) in the carbon dioxide molecule (CO2). 3 - the 133 figure is an estimate for all soils (forests, savanah, croplands, etc.), worldwide, since the beginnings of agriculture about 10-12,000 years ago. 4 - the United States Environmental Protection Agency (US EPA) has estimated that an automobile driven by the average person outs about 4.7 tonnes of CO2 into the atmosphere each year.

In nature, almost all of the N used by plants comes from bacterial N-fixers. Many of these are symbiotic bacteria, such as Rhizobium, but others are free-living bacteria.