Soil Fertility
IN THIS LESSON
Five things that improve soil fertility.
Earthworms
Earthworms facilitate the incorporation of organic matter into the soil by taking dead plant material from the soil surface into the soil where they feed on it. The material is transformed as it passes through their digestive tracts, becoming soil crumbs, which improve soil structure. The agro ecological farmer encourages earthworms by using mulch on the soil surface and by using no-tillage agriculture. Tillage means mechanically agitating the soil by, for example, digging, turning the soil over, and ploughing. The pH of the soil (how acid or alkaline it is) controls many chemical processes in the soil. Earthworms prefer near-neutral pH soil, moist conditions, and lots of plant residues on the soil surface.
Mycorrhiza
Mycorrhiza refers to a symbiotic relationship between a fungus and the roots of a plant. The fungus colonises the roots, and the plant and the fungus feed one another. Mycorrhizas are present in all soil types and serve to increase the uptake of water and nutrients, especially phosphorus.
Protozoa
Protozoa are unicellular microorganisms that crawl or swim in the water between soil particles. Many soil protozoa eat other microbes including bacteria. By eating and digesting bacteria, protozoa speed up the cycling of nitrogen from the bacteria, making it more available to crops.
Nematodes
Nematodes, also called roundworms, are multicellular organisms that are active in the soil. A handful of soil contains thousands of nematodes. Only a few species are harmful to crops. Nematodes speed up the nutrient cycle by eating decaying plant litter, bacteria, fungi, algae, protozoa, and other nematodes.
Algae
Unlike most other soil organisms, algae produce their own food through photosynthesis. Algae have a greenish film appearance on the soil surface and they improve the soil structure by producing substances that join soil together into water-stable aggregates. Some species of algae (the blue-greens) can fix nitrogen levels in the soil, which can be used by crop roots.
Most organisms are beneficial to agriculture, but some cause diseases, and some are parasitic. For example, certain fungi can cause a plant a net loss of energy. This may result in plant damage, e.g. wilting, rust, and rotting plant tissues. Practices that tend to promote a diverse variety of beneficial organisms in soil include adding organic matter, e.g. decomposed kitchen waste, returning crop residues to the soil, and rotating crops.