Home Composting: Microbiological Processes and Soil Improvement

Microbiological Processes and Determining Factors in Composting

Organic waste management at the household level presents a significant opportunity to close biogeochemical cycles and enhance the fertility of agricultural and garden soils. Composting, a biological process of controlled decomposition of organic matter under the action of aerobic microorganisms, allows the transformation of kitchen and garden waste into a nutrient-rich substrate, known as compost or organic fertilizer. This material not only improves soil structure, increasing its water retention capacity and aeration, but also provides essential organic matter for soil microbial life, promoting a healthy ecosystem.

Microbiological Processes and Optimal Conditions

Composting is fundamentally a microbial activity. Mesophilic and thermophilic bacteria, along with fungi and actinomycetes, are the primary decomposers. The initial stages of composting are characterized by the growth of mesophilic microorganisms (20-45°C), which rapidly consume sugars and starches present in fresh materials. As these compounds are depleted, microbial activity generates heat, raising the pile’s temperature to reach the thermophilic phase (45-70°C). This high temperature is crucial for sanitization, as it inactivates pathogens and weed seeds. Subsequently, as the availability of easily degradable compounds decreases, the temperature drops, and mesophiles, along with actinomycetes and fungi, predominate again, completing the composting maturation.

The effectiveness of the process depends on the correct proportion of ‘green’ materials (rich in nitrogen, such as fruit and vegetable scraps, coffee grounds) and ‘brown’ materials (rich in carbon, such as dry leaves, small twigs, unprinted cardboard). An ideal carbon-to-nitrogen (C:N) ratio ranges between 25:1 and 30:1. It is essential to ensure adequate aeration, either through periodic turning of the pile (every 1-4 weeks, depending on the method) or by using passively aerated composting systems. Moisture is also a critical factor; the pile should be kept moist, similar to a wrung-out sponge, without becoming waterlogged. A moisture content of 40-60% favors microbial activity.

Home Composting Methodologies and System Selection

Home Composting Methods

Various methodologies exist for implementing composting at home, adaptable to different spaces and waste volumes. The most traditional method is the outdoor compost pile, ideal for those with a garden. It is recommended to build the pile on bare soil to facilitate access for soil decomposers and drainage. Suggested dimensions are approximately 1m x 1m x 1m to optimize heat retention and aeration.

For smaller spaces, such as balconies or small patios, enclosed composters or vermicomposters are efficient alternatives. Enclosed composters, often made from recycled plastic, facilitate control of moisture and temperature, and minimize potential odor emissions if managed properly. Vermicomposters use red Californian earthworms (Eisenia fetida) to accelerate the decomposition of organic matter, producing high-quality compost known as worm castings. This method is particularly effective for kitchen waste and yields a final product highly valued in horticulture.

The choice of method will depend on the volume of organic waste generated, the available space, and the time that can be dedicated to management. A common practice to speed up the process is to shred or cut larger materials into smaller pieces, thereby increasing the surface area for microbial action. It is important to avoid adding meat, dairy, oils, and chemically treated materials, as they can attract pests, generate unpleasant odors, and contain unwanted compounds.

Agronomic Application of Compost and Benefits for Soil Health

Application and Benefits of Mature Compost

Compost is ready for use when it has reached a dark, earthy state, with a pleasant smell and no traces of the original materials. Its application in the garden or yard can be done in various ways. It can be mixed directly with the substrate of pots or growing beds before planting, providing nutrients and improving soil structure. Another technique is surface composting or ‘top dressing,’ spreading a thin layer of compost around established plants, allowing nutrients to gradually leach into the root zone with watering. It can also be used to make ‘compost tea,’ a liquid fertilizer obtained by steeping compost in water, rich in beneficial microorganisms and soluble nutrients.

The continued use of compost contributes to overall soil health, increasing organic matter, improving soil aggregation, which in turn favors water infiltration and reduces erosion. Microorganisms present in the compost can help suppress soil-borne diseases and improve nutrient availability for plants, reducing the need for synthetic fertilizers. The implementation of home composting, in addition to its agronomic benefits, aligns with circular economy principles, reducing the amount of waste sent to landfills and mitigating the emission of greenhouse gases associated with anaerobic decomposition in these sites. Initiatives promoted by environmental management and sustainable agriculture organizations often offer resources and guides for the correct implementation of these practices. For example, organizations like the EPA (Environmental Protection Agency) in the US or the RHS (Royal Horticultural Society) in the UK offer detailed information on techniques and management.

Home composting is a powerful tool for the conscious gardener and horticulturist, allowing the transformation of a waste stream into a valuable resource, promoting sustainability and the health of their crops and the environment.