It is not just a matter of semantics that differentiates dirt from soil. Dirt is comprised mainly of inert particles and lacks the vital nutrients necessary for plant growth. Soil, on the other hand, is alive and, as such, must be treated as a complex, yet delicately balanced entity that is the foundation of our food chain. Simply said, we must protect our soil and regenerate it when it has been depleted if we expect it to provide us with nourishing plants. Its vitality determines the quality of the life forms it supports.
Healthy soil teems with microscopic organisms that function as partners in the cycling of nutrients in the soil food web. Bacteria, fungi, mites, springtails, pseudoscorpions, nematodes and protozoa consume plant and animal matter, converting it into humus.
Humus is the organic, nutrient-rich component of soil. A poorly drained garden plot with too much clay in the soil would benefit from the addition of humus along with some coarse sand. The plant fibers in humus create air and water pathways in the compacted clay soil, improving drainage and enhancing the spread of roots. On the other hand, overly sandy soil that drains too rapidly would also be enriched by humus, which increases its ability to retain water. Like a sponge, humus readily absorbs moisture and slowly releases water, a factor that diminishes plant stress during drought.
In a single scoop of compost live thousands of different species of bacteria. In general, beneficial bacteria require oxygen to survive. These single-celled aerobic bacteria thrive in moist conditions and, when given oxygen, will proliferate. This is why turning the compost pile speeds up the decomposition process. Another way to ensure that oxygen reaches the lower portion of the compost pile is to place thick stems in a haphazard fashion at the bottom. I also prop a pole at the center of my bin, giving it a swirl each time I add to the pile. This creates a funnel that allows oxygen to reach the center without my having to flip the contents of my pile frequently.
In an oxygen-deprived environment, disease-causing, anaerobic bacteria proliferate. A waterlogged, compacted compost pile may smell of rotten eggs. When there is an excess of nitrogen rich material, such as a thick layer of fresh grass clippings, a pile may smell of ammonia. In this case, add carbon rich matter such as straw, shredded leaves or aged wood shavings to balance the nitrogen/carbon ratio.
Decomposition generates heat. If the temperature of the pile reaches 140 degrees, pathogens as well as many weed seeds are destroyed. Over 150 degrees, beneficial bacteria die. The heat is concentrated in the center of the pile so, to destroy pathogens, it is imperative to mix all the contents in the bin well to ensure that the entire batch gets hot enough. I do not compost meat, dairy or manure from carnivorous animals because it is difficult to ensure that the entire pile reaches 140 degrees.
Fungi decompose leaves and wood-based materials. Sawdust and wood shavings actually take up nitrogen as they initially decompose, so I do not add these to my compost bin until they have aged a year. Letting them winter over in the open also allows the snow and rain to wash away the tannins that inhibit decomposition. Hardwood leaves often take two to three years to fully decay, so I place them in a separate pile after shredding them with the lawn mower.