Use of Compost

Compost, vermicompost, pit humus, terra preta, humanure or ecohumus are all products of the degradation of organic wastes. Even though they vary somehow regarding composition and structure, they have similar functions when applied to the soil.

The process of thermophilic (high-temperature) composting generates heat (50 to 80° C), which kills the majority of pathogens present. The composting process requires adequate carbon, nitrogen, moisture, and air. The Double VIP, Fossa Alterna or Twin Pits for Pour Flush are ambient-temperature variations of high-temperature composting. In these technologies, there is almost no increase in temperature because the conditions in the pit (oxygen, moisture, C:N-ratio) are not optimized for composting processes to take place. Because of this, the material is not actually ‘compost’ and is, therefore, referred to as ‘pit humus’.

The texture and quality of the pit humus or composting products depends on the materials, which have been used for composting or have been added to the excreta (e.g., soil added to a Fossa Alterna) and the storage conditions. A variety of materials can be composted such as kitchen waste, garden waste, animal manure (cow dung, chicken dung, etc.). But also human urine and faeces are very valuable soil conditioners when properly produced and applied (see also small and large-scale composting, double ventilated improved pit, fossa alterna, twin pits for pour flush toilets, composting toilets, the arborloo, terra preta toilets or terra preta sanitation).

WHO guidelines on excreta use in agriculture (Volume IV) stipulate that compost should achieve and maintain a temperature of 50° C for at least one week before it is considered safe to use. Achieving this value, however, requires a significantly longer period of composting. For technologies that generate pit humus, a minimum of 1 year of storage is recommended to eliminate bacterial pathogens and reduce viruses and parasitic protozoa. WHO guidelines should be consulted for detailed information.

The basic use of compost-like products is conditioning and fertilising soil by the addition of humus, nutrients and beneficial soil bacteria. This helps improving the physical and chemical properties and contributes to enhance the capacity of the soil to store air and water.

Around the house, compost can be used on the lawns, for potted plants, trees and shrub plants, in the vegetable garden, as mulch, starter mixes. It is always important o incorperate the compost into the soil and to water well in order to protect it from the sun and to disperse the nutrients in the surrounding soil. The application technique varies according to what and where it is to be used. For instance, when compost is applied in the garden, simply add compost to your garden each year in spring or early summer before planting: Till the soil to a depth of 15 to 25 cm. Then, apply 10 cm of compost on top of the soil and till again to mix. If the soil is very poor, you can add some more compost (don’t worry about adding too much compost). Compost releases nutrients slowly and continuously and will not damage plants. Throughout the growing season you can add a sprinkle of compost mixed with soil as a top dressing (COMPOST CENTRE n.y.).

When using compost for the potted plants, potting soil can be made with 1/4 to 1/3 finished compost and the rest sterile soil or sand. You can also sprinkle a thin layer of compost over the house plant soil to add nutrients. This is also excellent to correct drainage problems in soils that have cracked or pulled away from the container. But do not put plants in pure compost. Plants need coarser particles such as sand and soil in order to root properly (COMPOST CENTRE n.y.).

Vermicompost is similar to compost, but as earth worms are used during the composting process, the resulting soil is particularly rich in nutrients, humic acids improving the structure of the soil. Earthworm castings in the home garden often contain 5 to 11 times more nitrogen, phosphorous, and potassium as the surrounding soil. Secretions in the intestinal tracts of earthworms, along with soil passing through the earthworms, make nutrients more concentrated and available for plant uptake, including micronutrients (AALOK et al. 2008, DICKERSON 2004). Moreover, the tunnels formed by the worms aid in the passage of water, which also washes the nutrients from the drilosphere to the roots that extend quite rapidly along these channels (AALOK et al. 2008, DICKERSON 2004).

Vermicompost can be used in many ways, such as a good germinator, potting mix, soil conditioner, tree planting media, seed inoculation and fertiliser replacement. It can be applied as pure cast or it can also be mixed with the garden soil. In pure form, castings provide a superior rate of germination. Vermicompost is a good potting media, suggested good mixture formula can be 5 to 10% vermicompost, mixed with any other potting medium that does not have a nitrogen demand. It will provide sufficient nutrition to sustain growth for up to six months. Vermicompost is also a good soil conditioner. Even in quite barren soils good sprinkling of vermicompost (around 2 to 3 mm thick), dug in and watered well, can improve harvests already in the first season. Another option to use vermicompost is for tree planting. A hand-spade of castings in the bottom of the hole dug for the tree will help ensure healthy growth right from the start (DWF 2009).

For seed inoculation take the seed and shake it together with vermicompost before you spread it. Vermicompost is also a good fertiliser due to its high C/N ratio: sprinkle it around the base of plants and dig it into the soil (DWF 2009).

Pit humus is a term used for composted human faeces, in particular the one from double ventilated improved pit, fossa alterna, twin pits for pour flush toilets, composting toilets, the arborloo, terra preta toilets or terra preta sanitation. It is produced passively underground at ambient temperatures and has a slightly different composition than other composting products (MORGAN 2007; TILLEY et al. 2013). To use pit humus as a soil conditioner it can be mixed into the soil before crops are planted, used to start seedlings or indoor plants or simply mixed into an existing compost pile for further treatment.

Terra preta (literally “black earth”) is a manmade soil recently discovered in the Amazon region that was produced by pre-Columbian cultures through the conversion of biowaste and faecal matter via lacto-fermentation and vermicomposting into long-term fertile soils. Terra preta soils have a specially high organic carbon content that allows for a long lasting fixation of essential nutrients, water retention and reduced leaching of nutrients from the rhizosphere. The nutrient rich humus in combination with the black carbon acts like a “microbial reef” that promotes and sustains the growth of mycorrhizae and other beneficial microbes, and it has been shown to retain its fertility for thousands of years (adapted from FACTURA et al. 2010). Terra preta products can be used or applied similar with the ordinary compost and vermicompost.

It has been shown that the productivity of poor soil can be improved by applying equal parts compost and top soil to it. The output from one Fossa Alterna should be sufficient for two 1.5 m by 3.5 m beds (MORGAN 2007) . In order to decide, which type of compost product is better for which type of soil, one must first know what set of organisms is needed in the soil (lacking in the soil); second, what set of carbon compounds are needed around the roots of the plants to grow the beneficial bacteria and fungi; and third, what organisms and kinds of carbons are in the different types of compost products.

In order to determine the quality of the compost, the most important things are: pH level, soluble salts, moisture, organic matter content, total nitrogen, carbon to nitrogen ratio (C:N), and other physical properties of the compost (e.g. structure).

A small risk of pathogen transmission exists, but, if in doubt, any material removed from the pit or vault can be further composted in a regular compost heap before being used or mixed with additional soil and put into a ‘tree pit’, i.e., a nutrient-filled pit used for planting a tree (see also small and large-scale composting). Compost and pit humus should not be applied to crops less than one month before they are harvested. This waiting period is especially important for crops that are consumed raw.

As opposed to sludge, which can originate from a variety of domestic, chemical and industrial sources, compost and pit humus have very few chemical inputs (see also pathogens and contaminants and health risk management). The only chemical sources that could contaminate compost or pit humus might originate from contaminated organic material (e.g., pesticides) or from chemicals that are excreted by humans (e.g., pharmaceutical residues). Compared to the chemicals that may find their way into wastewater sludge, compost and pit humus can be considered as less contaminated.

Compost and pit humus are inoffensive, earth-like products. Regardless, people might refrain from handling and using them. Conducting demonstration activities that promote hands-on experience can effectively show their non-offensive nature and their beneficial use (see also awareness raising).

The material must be allowed to adequately mature before being removed from the system. Then, it can be used without further treatment. Workers should wear appropriate protective clothing.