**3. Composting**

*Elements of Bioeconomy*

**90**

**Figure 2.**

*harvested mushrooms, respectively.*

*Mushroom cultivation processes. (a)–(g) represent substrate preparation, mixing and bagging, actively growing mushroom planting material (spawn), inoculation/spawning of substrate bags, Volvariella volvacea growing on banana leaves, and Calocybe indica (milky mushroom) growing on sawdust substrate and freshly* 

variety [11, 12]. They are conventionally grown on agro-industrial wastes containing lignin, cellulose and hemicelluloses. In Nigeria and other parts of the world, tons of these wastes are generated annually which, if not managed, will constitute a menace to the environment. Different agro-industrial wastes singly and in combination have been used for the cultivation of different mushrooms such as *Volvariella volvacea*, *Pleurotus* species, *Agaricus* species, etc*.* [13–15]. The waste used in mushroom production includes banana leaves, water hyacinth, sawdust, rice straw, maize

stover, corn cob, cassava peels, grass straws, oil palm processing wastes, etc.

maturity. Mushroom cultivation processes are presented in **Figure 2**.

The first step in mushroom growing is the choice of which mushroom species to grow. The culture of the choice mushroom can be obtained and prepared into the planting spawn, or the spawn is purchased directly from a mushroom laboratory. The second step is sourcing for a readily available substrate within the grower's immediate environment to cut down production cost. This step is followed by the preparation of the growing medium or substrate which may include chopping, breaking, soaking or moistening, depending on the type of substrate. They can be used fresh (rice straw, maize cob, banana leaves, etc.) or composted (sawdust). Some (straws, vines and wood) may require chopping into smaller sizes of 3–5 cm, while others can be used directly (e.g. sawdust) [16]. It is also required that the growth materials are disinfected to rid them of other inherent micro-organisms and insects by applying heat or chemical treatments [17, 18]. The third step in mushroom growing process is the transfer of the spawn or inoculum (planting material) to the growth medium after disinfection. This is done using a standard method in a laminar flow chamber or a locally fabricated inoculation hood, to avoid contamination of the disinfected substrate by unwanted micro-organisms. After inoculation or planting, the substrates are then moved to a dark room or incubation chamber and left for a period depending on the mushroom species that is being grown; it is a time during which the mushroom mycelium ramifies the entire substrate. After incubation, the substrates are subjected to a fruiting condition where the mushroom fruiting body initials or primordia begin to appear and are harvested after

Compost fertilizers are organic fertilizers made from plant and animal leftover that have been decomposed by the existing micro-organism [22, 23]. The main objective of making compost manure is to recycle these nutrients in plants and animal leftover back to the soil for plant growth. The practice improves the soil physical, chemical and biological activities, improving crop yields and nutritional values. It also maximizes the use of available organic resources on the farm and minimizes the use of costly inorganic agrochemicals [24, 25]. Process involved in making compost is referred to as composting. Composting is defined as a biological process in which a micro-organism converts organic materials such as manure, sludge, leaves, peels, animal waste and food waste into a soil-like material called compost in the presence of water and air [26]. It is the main process used to produce stable, high-quality organic fertilizers from organic waste [27]. Composting is done to transform and stabilize organic materials into stable, usable products, to produce uniform organic fertilizer suitable for soil amendment and to remove offensive odors, to kill weed seeds and pathogenic organisms [28]. Compost can be made from crop residues, husks, stovers and agricultural, domestic and industrial wastes that are accessible and available, combined with animal manures. Human wastes can also be composted for crop production, but it is not encouraged due to disease and pathogen transmission [29].

Nigeria is the leading producer of cassava in the world, producing 37 million tons/year on 2.5 million hectares of land [30]. Accompanied with this output is the large volume of cassava peels being released as waste by processing centres all over Nigeria. It is usually burnt or used to feed livestock (most especially small ruminants) as source of protein and roughages. However, not more than 10% of the cassava peels produced is utilized in feeding livestock. The remaining is commonly found in farm and other processing sites as heap that are generally perceived as a nuisance [28]. These materials, however, could be utilized more effectively and sustainably through recycling rather than being destroyed through burning as commonly practiced by many leading to air pollution. Wastes such as cassava peels are rich in crude protein (5.29%) and fat (1.18%) [31]. Utilization of the peels and other agricultural wastes is limited by its low digestibility. Composting will not only reduce toxicity but also convert the resistant lignocellulose material into a more digestible substrate. Preparing compost from wastes offers many advantages. It provides incentive for communities to recover locked nutrients in the wastes, eliminate the problem of waste disposal and increase the manurial values of the materials [32].

Compost can be prepared throughout the year. Three common methods of preparing composts include on the earth/flat surfaces, the use of compost pits and preparation in boxes. Methods adopted are dependent on availability and access to space (**Figure 3**).

Compost manure will regulate soil structure, softens hard soil and improves the water holding capacity of the sandy soil, thus increasing soil aeration and the soil's ability to withstand erosion by wind or water [25]. It requires little or no technical

#### **Figure 3.**

*Composting materials and matured compost; a, b, c and d are composting using bins, poultry manure, cassava peels and finished compost, respectively.*

know-how. It is cheap and can be made on-site where wastes are deposited, thus reducing cost of transport. As an organic fertilizer, it has the ability to release nutrient slowly into the soil, thereby making the effect to last longer, even to the succeeding crops. It creates a good environment for soil microbes, by providing carbon compounds which serve as nutrients for soil micro-organisms and other soil habitats. Compost manure due to its composition is the storehouse of all essential macro- and micronutrients required by plants. When composts are fortified with other amendments, it can be used to control plant diseases and reduce crop losses on the field. [30]'s report indicated that this type of product significantly reduced the need for pesticide, fungicide and nematode application, which could cause environmental pollution. Matured compost should conform to at least one of the four tests outlined below: (i) The carbon to nitrogen ratio (C: N) must be less than 25:1, and seed germination using radish in the compost is at least 90% of control. (ii) The compost is cured and does not reheat to 20°C above ambient temperature. (iii) The compost is cured and there is a 60% weight reduction of organic material. (iv) The material is cured under aerobic conditions without reheating.
