Organic farming
In order to obtain the greatest economic benefits in the shortest time, agricultural production today tends to be mechanised and uses a large amount of chemical fertilisers and pesticides in the production process. The production of chemical fertilisers and pesticides creates a huge ecological footprint. Intensive production and chemicals will damage the natural ecosystem and directly endanger the health of farmers, consumers and wildlife.
Organic farming focuses on the recycling of natural resources, abandoning the use of petroleum by-products such as chemical pesticides or chemical fertilizers, and using natural farming methods to maintain water and soil and produce healthy crops. It is based on the rhythm of nature, which not only reduces unnecessary resource consumption and waste emissions, but also maintains the regeneration capacity of the natural system.
Organic farming is a method of farming that is in harmony with the natural environment, growing a variety of crops and coexisting in harmony with nature's biodiversity:
- No use of chemical pesticides, chemical fertilisers
- Planting arrangements are based on natural seasons and environment
- Maintaining soil long-term productivity
- Avoid damage to the ecological environment
- Reduce energy consumption
What is composting?
Composting imitates the cycle of nature by piling together organic matter that is originally called garbage but can be biodegraded (such as fallen leaves, dead grass, animal carcasses and excrement), providing a suitable environment for various animals and microorganisms to decompose them at a higher rate. During the process, the decomposed organic matter will release heat and carbon dioxide. It eventually transforms into a dark brown, earthy-smelling, high-nutrient humus called compost.
Why do we need compost?
Recycling of kitchen waste
Food waste accounts for 1/3 of Hong Kong’s garbage.
In 2011 (the base year), Hong Kong people discarded about 3,600 tonnes of food waste every day, of which two-thirds came from households (about 2,500 tonnes) and one-third came from food-related commercial and industrial sources (about 1,100 tonnes).
Currently, most of the food waste in Hong Kong is disposed of at landfills together with other municipal solid waste. In 2022, about 11,130 tonnes of municipal solid waste were disposed of at landfills every day, of which about 3,300 tonnes (30%) were food waste, the largest category of disposed municipal solid waste. Of the food waste dumped in landfills every day, about 1,000 tonnes comes from the commercial and industrial sectors, including restaurants, hotels, wet markets, food manufacturing and processing industries, etc. Moreover, due to the lack of oxygen, it is very difficult to decompose. The decomposition process will also produce harmful methane (marsh gas) and may leak sewage, causing environmental problems.
Composition of municipal solid waste (MSW) in Hong Kong in 2012
The current practice of disposing of food waste in landfills is not in line with the principle of sustainable development and also has adverse impacts on the environment. These organic wastes not only take up valuable landfill space, but also decompose and produce odors, requiring further proper treatment of leachate and greenhouse gases, and also waste the useful organic matter.
Incineration, another common method for dealing with solid waste, is even less suitable for organic waste. This method is not only expensive, but also has poor combustion effects and low efficiency due to the high water content of most organic matter. It also produces more waste gas and highly toxic organic pollutants, requiring more resources to process and remove.
If these solid wastes are composted and turned into useful soil conditioners, not only can the resources be reused, but the volume of the waste will also be greatly reduced after composting, greatly saving the cost of processing, storage and transportation.
Compost is a natural soil conditioner
If compost is mixed with soil, it can improve the structure of the soil, adjust the pH of the soil, and make the originally loose sandy structure compact, improving water retention, air permeability, drainage and fertilizer retention, etc. It can also provide balanced basic nutrients to plants, making it an excellent soil conditioner.
Carry out composting in schools or communities to raise environmental awareness
Many environmental education and civic education activities involve "recycling". Composting is not only relevant to this topic, but also allows participants to directly experience it and explore the thorny issue of waste disposal from another perspective.
Increase soil biodiversity
The composting process involves a large group of organisms breaking down organic matter. Bacteria are the smallest but most abundant organisms in compost. In a compost pile, about 80-90% of the microorganisms are bacteria, which break down organic matter into simpler forms so that other microorganisms can continue to work. Other organisms, such as fungi, secrete enzymes to break down organic matter and then absorb the nutrients contained therein. This form of decomposition can be called chemical decomposition.
The contribution of invertebrates (such as earthworms, snails, millipedes, centipedes, etc.) in the compost pile can be called physical decomposition. They break up materials through activities such as chewing, sucking, and excretion, increasing the surface area of the materials for microorganisms to work on. At the same time, it will loosen the material, allowing more air to enter the center of the compost pile. When they die, they leave behind debris that provides raw materials for microorganisms to decompose.
Common organic compost ingredients, properties and uses
We often use organic compost of animal and plant matter to degrade it with microorganisms. This process is called composting, which is divided into aerobic composting and anaerobic composting.
Traditional composting often uses anaerobic field stacking methods, which occupy a large area, take a long time to stack, and have a low degree of harmlessness. Modern composting production methods usually use aerobic composting, which is monitored by electrical instruments and controlled by machinery. The composting process is large, the fermentation speed is fast, the degree of harmlessness is high, and the compost composition is stable and safe.
Aerobic composting is usually divided into the following four processes, which are key steps for the quality of organic fertiliser:
1. Step 1: Pre-treatment
It mainly collects the deposited materials, removes impurities such as plastic, metal, stone, etc., and controls the moisture content. If the moisture content is below 30%, the reproduction of microorganisms will be inhibited, which will affect the fermentation; if the moisture content is higher than 70%, the aeration will be reduced and there will be insufficient air. In severe cases, it will turn into anaerobic fermentation, which will slow down the compost fermentation speed. Therefore, it is most appropriate to control the moisture content at 55% to 65%, and the pH value of the stacking material should be adjusted to around pH 7.
2. Step 2: Primary Fermentation
It is usually carried out in a specific fermentation device or place. The microorganisms that decompose organic matter during fermentation are aerobic microorganisms, so oxygen supply is very important. Oxygen can be introduced into the compost through automatic stirring and turning or ventilation equipment to facilitate aerobic fermentation. When there is insufficient oxygen, anaerobic microorganisms will proliferate, making decomposition difficult and producing ozone such as hydrogen sulfide; but if the air supply is too large or the stirring is excessive, the fermentation temperature will drop and water will be lost quickly, affecting the fermentation speed.
The period from when the temperature starts to rise to when it starts to drop is usually called primary fermentation, which lasts at least 10 days. If it is cow dung composting, it is 4 to 5 weeks, pig manure is 3 to 4 weeks, and chicken manure is 2 to 3 weeks.
3. Step 3: Secondary Fermentation
After the first fermentation, there are still easily decomposable and a large amount of difficult-to-decompose organic matter in the material, which are sent to the secondary fermentation site for further decomposition. The pile height is about 1 to 2 meters. During the process, the pile is turned over every 1 to 2 weeks and will gradually be transformed into a more stable and mature compost. When the internal temperature of the compost drops to about 40℃, it is mature, which usually takes about 20 to 30 days. Composting pure poultry and livestock manure takes about 1 month, adding stem materials takes about 2 to 3 months, and adding wood materials such as sawdust and bark takes 6 months.
4. Step 4: Post-processing
This stage mainly involves removing residual impurities from the fully fermented compost, crushing and granulating it, and finally packaging or directly storing it.
Figure 1 Composition, properties and uses of commonly used organic compost fertilizers
When organic materials are fermented through the composting process, the temperature can reach as high as 60℃ to 80℃. Most pathogens, insect eggs, and weed seeds will be destroyed at this temperature, and even after the fertiliser is fully decomposed, it will not generate fermentation heat to harm the crop roots.
The moisture content of fully decomposed organic fertiliser drops below 35%, at which point the microbial activity stops and the fertiliser can be stored for a long time without changing its quality. After being fully decomposed, the fertiliser composition is stable and uniform, which can also avoid uneven crop growth, harm to crops or damage to the soil after application.
If livestock and poultry manure (such as raw chicken manure, raw pig manure, and raw cow manure) is applied directly without being fully decomposed, it may carry pathogens, insect eggs, weed seeds, etc. If used rashly, it may cause massive damage to crops. In order to prevent animals from getting sick or being infected by insect pests, some feeds contain heavy metals such as zinc or copper, which directly affects the quality of animal manure. If such organic materials are used as fertilisers, they may cause heavy metal pollution in the soil or be absorbed by crops, and even affect the health of consumers.
Food waste composting
About 3,000 tonnes of food waste is generated in Hong Kong every day from restaurants, food factories and households. Household kitchen waste includes fruit peels, vegetable leaves and leftovers, which are an inevitable part of household garbage. They are easy to rot, stink and seep water, causing trouble in garbage removal. If kitchen waste is turned into organic fertilizer through composting and then returned to the earth, it is the best way to complete the cycle of organic matter and reduce waste.
Food waste collection
The most discarded garbage by Hong Kong people is "kitchen waste". In our daily lives, we may have a lot of leftover food every day. Meat, soup residue, and fruit peels can also be recycled. These kitchen wastes often become garbage and are sent to landfills. More than 3,000 tonnes of food waste is discarded in Hong Kong every day, accounting for nearly 30% of municipal solid waste and is the largest type of garbage. Food waste is easily decomposed and creates odor and hygiene problems, taking up valuable landfill space and wasting the useful organic matter contained therein.
The Environmental Protection Department currently has "Smart Food Waste Bin" installed in 217 public housing estates in Hong Kong, Kowloon and the New Territories. Smart recycling bins with overflow prevention and odour removal devices are used to collect food waste to maintain a clean environment. "Green Rewards" smart points rewards are also provided to encourage residents to participate and gradually change their lifestyle habits.
(Left) The Environmental Protection Department will install "smart food waste machines" in 217 public housing estates in Hong Kong, Kowloon and the New Territories in 2024, (Middle) and restaurants carry out food waste recycling in Harbour City, a large urban property management collection, owned by Wharf Group; and (Right) O PARK1 Food Waste Recycling Centre in Siu Ho Wan, North Lantau Island
Introduction and operation of the first Organic Resource Recovery Centre (O.PARK1) in Hong Kong
Trash can covering method
- Take a 50-liter (or larger) covered trash can, cut off the base, choose a cool place, bury the can in the mud about 5-10 cm deep, and sprinkle lime on the edges (to prevent rats and cockroaches from infesting).
- After draining the water from the kitchen waste, spread a layer of soil on top of the kitchen waste and process it day by day.
- Cover the lid of the trash can with a thick cloth, or cover it with a large plastic bag and tie it with a rope to keep out insects and flies.
- Once the compost bin is full, leave it there for 3-5 months. If there is no bad odor, the composting is successful.
- To use the compost, scoop out appropriate amounts from the bottom of the bucket in batches.
Detergent Bucket
- Add a faucet to the side of an empty laundry detergent bucket (a round bucket with a twist-off lid or a square box will do, remember to clean the contaminants on the inside).
- First add bricks to the bottom and then place a wire mesh with a 2.5 cm mesh (to separate slag).
- In addition, an empty plastic bottle is hung with wire under the faucet.
- Chop the daily kitchen waste into small pieces, put it into a bucket, stir it slightly, and cover the bucket.
- Every night before going to bed, turn on the faucet to let the smelly water flow into the plastic bottle, and immediately flush it down the toilet.
- When the compost bin is full, leave it for another month (with continuous drainage), then find a suitable location (such as an open space or a large flower pot) to bury the compost in the soil or mix it with other soil for later use.
- When making organic compost at home, it is advisable to use plant materials as kitchen waste, such as vegetable stems, leaves, and fruit peels. Cut, chop and drain them when processing them daily, or mix them with some shredded old newspapers or used toilet paper, and stir them slightly before covering the compost bin. This can reduce the odor produced during composting. You may want to give it a try.
Worm Composting
Worm composting mainly utilizes the earthworms' ability to digest organic matter. They eat the organic matter, excrete it after digestion, and turn it into smaller and simpler substances. They then eat these excrement again. The whole process is repeated many times, and finally the organic matter is turned into useful fertilizer.
Earthworms eat organic matter, digest it and excrete it, and the whole process is repeated many times, eventually turning the organic matter into useful fertilizer.
Material︰
(1) A wooden box/plastic barrel (the size depends on the number of fish you are keeping, and can be anything from a lunch box to a trash can)
(2) A pile of gravel (enough to fill the bottom of the box/barrel)
(3) A piece of screen (laid flat on the gravel layer to prevent earthworms and soil from falling)
(4) A pile of soil (it is the living space of earthworms; if there are more earthworms, there should be more soil; if there are fewer earthworms, there can be less soil)
(5) At least two earthworms (earthworms are hermaphrodites and cross-fertilization occurs)
(6) Cardboard/Newspaper/A cover (to block out light and reduce moisture loss)
(7) A watering can (to keep the soil moist)
Preparation method:
- Place the gravel in a wooden box/plastic bucket (if necessary, add two holes at the bottom of the box or bucket to drain water).
- Cover with gauze and put in soil and earthworms.
- Put a small amount of food on the mud surface and observe how much the earthworms eat.
- Initially, the earthworms may still be adapting to the new environment and may not eat much. But after about a week, when the earthworms have adapted to the new environment, they will eat a lot and reproduce. Remember to add food to them and keep the environment moist.
- After 3-4 months, you can start harvesting. First, open the lid for a while to let the earthworms hide in the lower layer of soil. Then you can take the upper layer of soil and the earthworm manure and use it as fertilizer.
If your earthworms are introduced from other places, they may grow faster and be easier to raise, but never release them into the land or nature, because we still don't know what impact they will have on local earthworms. In order to avoid the recurrence of problems like micrantha, it is better to be cautious.
If you encounter any technical difficulties, you can email the Earthworm Bulletin Board Service (earthworm@julian.uwo.ca) and they have 40 earthworm experts from different countries to answer your questions.
Earthworms are natural soil tillers. The Rodale Institute estimates that if there are 1 million earthworms living in every acre of soil, it is equivalent to three gardeners taking turns working on the field for 8 hours a day.
Reference
- Mr. Ye Maosheng, Introduction to Agriculture, 1994. (in Chinese)
- Organic Farming Basics, 綠田園基金 Produce Green Foundation (in Chinese)
- A Hong Kong Food Waste and Yard Waste Plan, 2014-2022
