Building Digital Education of Heirloom Crops
for the Resilience of African Food Systems in the Climate Crisis
Lecture 2
Indigenous Production Methods
Healthy soil is the key to a solid and productive farm
Feed the soil, and the soil will feed your plants
Soil is a living system that is much more than just a substrate for plant growth. It is home to billions of microorganisms that form a complex ecosystem together with plant roots. This ecosystem is essential for plant health, development, and resistance to diseases and pests.
Through interaction with soil, humans can deplete, degrade, or, by wisely collaborating with soil microorganisms, "build" it. Building soil is a long-term investment that rewards the farmer. When a farmer cares for soil fertility—literally "growing the soil" or feeding the soil-forming microorganisms with organic matter—the fertile soil layer becomes thicker year after year. Plants grow more vigorously, have stronger immunity, and are better able to resist diseases and pest attacks.
Soil ecosystem
The healthy soil ecosystem is a complex network of interconnected organisms. Physical factors like texture and moisture influence its structure. Organic matter provides nutrients and energy. Microorganisms break down organic matter, cycle nutrients, and form soil aggregates. Macroorganisms like earthworms and insects contribute to soil structure and aeration. Plant roots provide food for microbes and help anchor the soil. Together, these components create a dynamic and interconnected soil food web that supports plant growth and overall ecosystem health.
![Drawing by Edvards Putans; Source: Brackin R et al., Soil biological health[..]](https://static.wixstatic.com/media/8b6f1b_0f8b0ef6f6bd4ad9bf29feeb322299d4~mv2.jpg/v1/fill/w_980,h_1386,al_c,q_85,usm_0.66_1.00_0.01,enc_avif,quality_auto/8b6f1b_0f8b0ef6f6bd4ad9bf29feeb322299d4~mv2.jpg)
The symbiosis between plant roots and microorganisms is a highly complex biochemical process. Early in a plant's life cycle, it releases higher sugar levels to attract cooperative microbes. In response, bacteria and fungi that detect these exudates move toward the roots and establish microscopic niches on, around, between, and sometimes inside the roots. In exchange for sugars from the plant, microbes provide the plant with nutrients and water, and protection from parasitic organisms and drought. [1]
The rhizobiome, the intricate community of microorganisms residing in plant roots, is a susceptible system and is heavily impacted by the presence of any chemical substances. Chemical fertilizers disrupt this symbiosis; the plant no longer needs to produce and release sugars because nutrients are readily available, thus leaving soil microorganisms without food and causing them to die. In this way, artificial fertilization destroys life in the deeper soil layers, and restoring it isn't easy.
The root microbiome inhabits a narrow zone around plant roots. Fungi and bacteria consume plant exudates, and in exchange they provide plants with nutrients and metabolites essential for growth and health. Sorce Montgomery and Biklé/The Hidden Half of Nature, 2016.
As a gardener, you can actively promote soil health:
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Feeding the soil: Regularly adding organic matter (compost, green manure) provides food for microorganisms and encourages the formation of a fertile layer.
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Protecting the soil: Avoid deep plowing, which damages soil structure and destroys microorganisms. I prefer mulching and shallow soil tillage.
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Diversifying plants: Planting a variety of plants promotes soil biodiversity and improves its ability to retain water and nutrients.
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Using natural fertilizers: Prefer compost, manure, and green manure over artificial fertilizers, which can deplete the soil.
Healthy soil is a long-term investment. By regularly caring for soil health, you provide your plants with everything they need to grow strong and healthy and reduce the need for pesticides and other chemicals.
Restoring soil fertility through natural techniques
Mulching[2]* – Mulch is any material spread over the soil to protect and improve health. Mulch acts as a protective cover for the soil, serving several essential functions:
*Mulching is a gardening technique that covers the soil around plants with organic or inorganic materials.
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Mulch acts as a barrier that reduces water evaporation from the soil, thus keeping it moist for longer. This is especially important during dry periods.
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A layer of mulch blocks the sunlight needed for weed germination and growth, reducing the need for weeding.
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In summer, mulch helps protect the soil from overheating; in winter, it protects it from freezing. It provides a more stable topsoil temperature, benefiting plant roots and soil microorganisms.
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As organic mulch decomposes, it enriches the soil with organic matter and improves its structure and aeration. The nutrients it gradually releases are available to plants.
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Mulch helps reduce soil erosion caused by rain and wind.
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Different types of mulch can improve the appearance of a garden and give it a well-maintained look.
Mulch can consist of leaves, grass clippings, hay, straw, compost, bark, wood, peat, and pebbles. Different materials can have slightly different effects on the soil:
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Hay: Diverse plant composition, providing a variety of nutrients for soil microorganisms upon decomposition; usually not treated with pesticides; better C:N ratio than other materials, therefore composts better; even spoiled hay, unsuitable for animal feed, can be used; retains moisture well and provides good thermal insulation, yet does not hinder air circulation.
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Wood, bark, and leaves: Contain a large store of nutrients; feed fungi; significantly promote water retention in the soil.
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Grass clippings, including grass silage, are a delicacy for soil microorganisms and provide balanced and readily available nutrients for plants.
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Straw may contain pesticides and other chemicals that can contaminate your soil and even inhibit plant growth. It is also poor at retaining moisture. It has a uniform composition, but it composts slowly and provides less nutrition to the soil compared to hay.
Composting [3] – Composting is a natural process that has been occurring for millions of years. In the forest, where leaves, branches, and other plant debris fall, microorganisms work, transforming this organic material into humus – the fertile layer of soil.
Humans have learned to accelerate and optimize this process with targeted material selection to ensure an optimal carbon-to-nitrogen ratio and active intervention by turning the compost*, providing access to air and moisture, or building it the most efficiently.
*Compost is a mixture of decayed or decaying organic matter fertilizing soil. It is usually made by gathering plant material, such as leaves, grass clippings, and vegetable peels, into a pile or bin and letting it decompose through the action of aerobic bacteria, fungi, and other organisms.
Composting offers numerous benefits for soil health and sustainability. It creates a natural fertilizer rich in nutrients that can enhance soil fertility. Compost also improves soil structure, allowing it to absorb and retain water better. Additionally, it's a haven for beneficial microorganisms that promote plant growth and overall soil health. Composting organic waste reduces the amount of material sent to landfills, contributing to a more sustainable environment.
What do microorganisms need in compost?
Just like us, they need:
Carbon: provides energy for microorganisms and is found in wood chips, leaves, and straws.
Nitrogen: Essential for growth and reproduction of microorganisms. It's found in grass clippings, food scraps, and manure.
Moisture: Microorganisms need water to carry out their activities.
Oxygen: Most composting microorganisms require oxygen.
C:N ratios in home compostable materials
C:N ratio stands for the ratio of carbon to nitrogen in organic materials. It's a crucial factor in composting because it affects how quickly materials decompose and whether the compost pile heats up enough to kill pathogens.
Generally, a good C:N ratio for home composting is between 25:1 and 30:1. For every 25-30 carbon parts, you should have 1 part of nitrogen.
More about bacteria
When we compost, we are essentially creating a thriving ecosystem of microorganisms. Aerobic bacteria are the workhorses of this ecosystem because they require oxygen to break down organic matter. These bacteria can be categorized into three main groups based on their optimal temperature range:
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Psychrophiles: These are typically the first bacteria to appear in cold temperatures (4-15°C). They produce amino acids, feed on lignin and cellulose (wood), and can work even in winter.
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Mesophiles: These are the second wave of moderate-temperature bacteria (18-30°C) and are usually the most common. Among them are actinomycetes (a hybrid of fungi and bacteria), the actual finishers of the decomposition process, creating those beautiful gray spider webs.
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Thermophiles: These are high-temperature metabolizers that make your compost heat up. They are also the most productive.
Compost bacteria. Sorce Compost Magazine.
Why are aerobic bacteria so important?
They convert organic matter into nutrient-rich humus, which is essential for plant growth. Additionally, they help reduce the volume of organic waste and can improve soil structure and water-holding capacity.
What about anaerobic bacteria?
In contrast, anaerobic bacteria do not require oxygen. While they can also break down organic matter, they often produce unpleasant odors and create conditions that favor the growth of plant pathogens.
Methods of composting
Sheet composting is a simple and sustainable method of improving soil health. Instead of creating a compost pile, you spread organic materials directly on the soil surface. Over time, microorganisms break down these materials, enriching the soil with nutrients and improving its structure. This method is ideal for large areas or for preparing garden beds for planting. It requires less labor and helps suppress weeds, improving soil moisture retention.
Direct composting in beds is a low-maintenance method that requires minimal effort. Materials are layered directly onto the garden bed and allowed to decompose naturally. This process is slow but beneficial for soil health. The three-bin method helps maintain a continuous supply of compost. It's an excellent option for those seeking a sustainable and hands-off approach to composting.
Three-pile system – cold composting. A variant for those with plenty of time and material, composting in layers.
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First pile: Accumulates fresh material, striving to maintain a C:N ratio of 30:1. It is preferably layered (C-N-C-N-C).
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Second pile: Transferred from the first when the pile cools (at least 3-4 months), the process is activated, the material is mixed, and the temperature rises.
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Third pile: The second pile is transferred when it has collapsed and cooled (the following spring?), the compost matures, and worm activity increases.
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In Latvia, the third phase of composting can last throughout the second summer, and good compost is obtained only in the third season.
Three-bin system - hot composting. Optimizes and accelerates compost formation but is labor-intensive.
This method involves three bins and focuse on maintaining a high temperature to speed up the composting process. The high temperatures generated in the first bin are due to the rapid activity of thermophilic microorganisms. These heat-loving organisms break down organic matter quickly.
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Bin 1: Fresh organic materials are added and regularly mixed to maintain a high temperature, but keeping it lover in the center than 65°C
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Bin 2: After the initial hot phase, the material is moved to the second bin where mesophilic (moderate temperature) organisms continue the decomposition process.
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Bin 3: This bin holds the finished compost, ready for use.
![Figure from research [4]: Temperature evolution during the composting process [4]](https://static.wixstatic.com/media/8b6f1b_adcd6c55a5fb4a14b3544d83880e6abb~mv2.jpg/v1/fill/w_485,h_307,al_c,q_80,enc_avif,quality_auto/8b6f1b_adcd6c55a5fb4a14b3544d83880e6abb~mv2.jpg)
Nikoloudakis et al. (2018). Composting as a Service: A Real-World IoT Implementation. Future Internet. 10. 107. 10.3390/fi10110107.
Hot Compost. Hot composting is a method that speeds up the composting process by maintaining a high temperature within the compost pile. This is achieved by frequently turning the compost to introduce oxygen and mixing the materials.
It requires more effort as materials need to be shredded, mixed, and watered, maintaining an optimal minimum volume of at least 1 cubic meter.
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Must be turned at least every three days (optimal temperature 55-60°C).
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Compost is usually ready in about 14 days, but if there's time for mesophilic bacteria and fungi to work, it's even better.
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Excellent for new gardens or areas with long cold seasons like Latvia.
Refferences:
[1] - Clutter, Christy Ph.D. (2021). Unearthing the Soil Microbiome, Climate Change, Carbon Storage Nexus. American Society for Microbiology. https://asm.org/Articles/2021/May/Unearthing-the-Soil-Microbiome,-Climate-Change,-Ca
[2] - Zalamane, Guna., Kilupe, Daira (2024). Lecture "Soil fertility enhancement, biodiversity in the garden", Seed savers' course organized by LPA. [restricted availability]
[3] - Larrive, Mike P.G. (2017). Lecture "The Art and Science of Composting: Restoring Function in Soils", Latvian Permaculture Festival organized by LPA. https://docs.google.com/presentation/d/1KQETdy2AIaBfgL2QNjS-wxobmEjz_QZe/edit?usp=sharing&ouid=100422232736659187716&rtpof=true&sd=true
[4] - Nikoloudakis, Yannis & Panagiotakis, Spyridon & Manios, Thrasivoulos & Markakis, Evangelos & Pallis, Evangelos. (2018). Composting as a Service: A Real-World IoT Implementation. Future Internet. 10. 107. 10.3390/fi10110107.
The content of this page was created as part of the project 'Building Digital Education of Indigenous Inherited Crops for the Resilience of African Food Systems in the Climate Crisis Development.' The project was funded by the Ministry of Foreign Affairs in 2024 from the development cooperation budget. This content reflects only the views of the project partners.
