Humus in the context of "Soil retrogression and degradation"

Soil retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a stable soil. Retrogression is primarily due to soil erosion and corresponds to a phenomenon where succession reverts the land to its natural physical state. Degradation or pedolysis is an evolution, different from natural evolution, related to the local climate and vegetation. It is due to the replacement of primary plant communities (known as climax vegetation) by the secondary communities. This replacement modifies the humus composition and amount, and affects the formation of the soil. It is directly related to human activity. Soil degradation may also be viewed as any change or ecological disturbance to the soil perceived to be deleterious or undesirable.

According to the Center for Development Research at the University of Bonn and the International Food Policy Research Institute in Washington, the quality of 33% of pastureland, 25% of arable land and 23% of forests has deteriorated globally over the last 30 years. 3.2 billion people are dependent on this land.

Dirt is any matter considered unclean, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty.Common types of dirt include:

• Debris: scattered pieces of waste or remains
• Dust: a general powder of organic or mineral matter
• Filth: foul matter such as excrement
• Grime: a black, ingrained dust such as soot
• Soil: the mix of clay, sand, and humus which lies on top of bedrock. The term 'soil' may be used to refer to unwanted substances or dirt that are deposited onto surfaces such as clothing.

Termites are a group of detritophagous eusocial cockroaches which consume a variety of decaying plant material, generally in the form of wood, leaf litter, and soil humus. They are distinguished by their moniliform antennae and the soft-bodied, unpigmented worker caste for which they have been commonly termed "white ants"; however, they are not ants but highly derived cockroaches. About 2,997 extant species are currently described, 2,125 of which are members of the family Termitidae.

Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blattodea (the cockroaches). Termites were once classified in a separate order from cockroaches, but recent phylogenetic studies indicate that they evolved from cockroaches, as they are deeply nested within the group, and the sister group to wood-eating cockroaches of the genus Cryptocercus. Previous estimates suggested the divergence took place during the Jurassic or Triassic. More recent estimates suggest that they have an origin during the Late Jurassic, with the first fossil records in the Early Cretaceous.

Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical, and biological properties. It is commonly prepared by decomposing plant and food waste, recycling organic materials, and manure. The resulting mixture is rich in plant nutrients and beneficial organisms, such as bacteria, protozoa, nematodes, and fungi. Compost improves soil fertility in gardens, landscaping, horticulture, urban agriculture, and organic farming, reducing dependency on commercial chemical fertilizers. The benefits of compost include providing nutrients to crops as fertilizer, acting as a soil conditioner, increasing the humus or humic acid contents of the soil, and introducing beneficial microbes that help to suppress pathogens in the soil and reduce soil-borne diseases.

At the simplest level, composting requires gathering a mix of green waste (nitrogen-rich materials such as leaves, grass, and food scraps) and brown waste (woody materials rich in carbon, such as stalks, paper, and wood chips). The materials break down into humus in a process taking months. Composting can be a multistep, closely monitored process with measured inputs of water, air, and carbon- and nitrogen-rich materials. The decomposition process is aided by shredding the plant matter, adding water, and ensuring proper aeration by regularly turning the mixture in a process using open piles or windrows. Fungi, earthworms, and other detritivores further break up the organic material. Aerobic bacteria and fungi manage the chemical process by converting the inputs into heat, carbon dioxide, and ammonium ions.

Biodegradable waste includes any organic matter in waste which can be broken down into carbon dioxide, water, methane, compost, humus, and simple organic molecules by micro-organisms and other living things by composting, aerobic digestion, anaerobic digestion or similar processes. It mainly includes kitchen waste (spoiled food, trimmings, inedible parts), ash, soil, dung and other plant matter. In waste management, it also includes some inorganic materials which can be decomposed by bacteria. Such materials include gypsum and its products such as plasterboard and other simple sulfates which can be decomposed by sulfate reducing bacteria to yield hydrogen sulfide in anaerobic land-fill conditions.

In domestic waste collection, the scope of biodegradable waste may be narrowed to include only those degradable wastes capable of being handled in the local waste handling facilities. To address this, many local waste management districts are integrating programs related to sort the biodegradable waste for composting or other waste valorization strategies, where biodegradable waste gets reused for other products, such as using agricultural waste for fiber production or biochar.

Loam (in geology and soil science) is soil composed mostly of sand (particle size > 63 micrometres (0.0025 in)), silt (particle size > 2 micrometres (7.9×10 in)), and a smaller amount of clay (particle size < 2 micrometres (7.9×10 in)). By weight, its mineral composition is about 40–40–20% concentration of sand–silt–clay, respectively. These proportions can vary to a degree, however, and result in different types of loam soils: sandy loam, silty loam, clay loam, sandy clay loam, silty clay loam, and loam.

In the United States Department of Agriculture, textural classification triangle, the only soil that is not predominantly sand, silt, or clay is called "loam". Loam soils generally contain more nutrients, moisture, and humus than sandy soils, have better drainage and infiltration of water and air than silt- and clay-rich soils, and are easier to till than clay soils. In fact, the primary definition of loam in most dictionaries is soils containing humus (organic content) with no mention of particle size or texture, and this definition is used by many gardeners. The different types of loam soils each have slightly different characteristics, with some draining liquids more efficiently than others. The soil's texture, especially its ability to retain nutrients and water, are crucial. Loam soil is suitable for growing most plant varieties.