Written By Lau Hoi Lung. Translated by Angeline Chan.

Soaring property prices, shortage of elderly homes, lack of places for people to enjoy intimate relationships – it seems as though no social problem in Hong Kong is far removed from land issues. The government keeps banging on about limited land supply, lending credence to the saying “Hong Kong is a densely populated city”. Studies on low interest rates and injustice in land distribution have already shown that this saying may well be false. Putting this aside, is it true that building housing is the most important use of land? To form a better idea of what our ideal city should look like, we need to address collusion between the government, developers, rural interests and triads – and more importantly, we should have a renewed understanding of land. The writer will start from soil – one thing that city dwellers give little if any thought to.


Soil is made of more than sand and stones. In fact, it is primarily made of three parts. Almost half consists of minerals from the weathering erosion of rock and sedimentation of eroded materials. Soil formed from the erosion of tuff (a kind of volcanic rock) or from river bank sediments is the most fertile. Soil from granite is less fertile, and least fertile is soil from sedimentary rocks. The other portion of soil consists of the gaps occupied by air and water. When the soil is dry, air is dominant; when it is damp, water displaces the air in bubbles. The size of grains in the soil determine capacity for water retention and drainage. The third and smallest portion, at about 5%, is organic matter. Yet this is precisely the determining factor of fertility, and even the key to human survival.

Organic matter is formed by the decomposition of organisms. On a hike, brushing away fallen leaves on the ground will reveal humus, which is decaying organic matter. Incredible things occur on the microscopic level. Microorganisms and the hyphae of fungi bind different minerals together, creating soil aggregates of different sizes. These aggregates are not easily compacted, and between them allow for a balance between air and water. These aggregates carry nutrients and form the perfect medium for plants to thrive. Without organic matter, soil would become like sand on the beach: loose, disconnected, and incapable of carrying moisture. In fact, much of the nutrients absorbed by plants are excretions from microorganisms living in the soil.

The quantity of organic matter in soil turns on a few factors: the amount of fallen leaves; the speed of their decomposition; and speed of their further transformation into gases such as carbon dioxide. There is a common misconception that tropical rainforests, being the most diverse ecosystems, are richest in decomposing matter. In fact, due to the high temperature and humidity, fallen leaves quickly decompose and turn into gases. Grasslands in temperate climates actually have higher portions of decomposing matter. Hence the famed “black earth” regions of Ukraine, the US and North-eastern China. To summarize, the fertility of soil is determined by the intertwining factors of geology, climate, and accumulation of organic matter. Apart from these natural factors, the human process of growing food is another essential factor affecting soil fertility.


A famed line from local film Overheard 3 (2014) goes: “land is for nurturing life.” Yet it is undeniable that farming does affect soil and the underlying ecosystem. As our ancestors shifted from being hunter-gatherers to growers, we gained control over land. We classified plants that we could not eat as weeds and thought of them as our crops’ competitors for nutrients and space. We classified animals that ate crops as pests, and those which ate pests as beneficial. We thus passed judgments of “good” or “bad” upon natural processes, which in themselves have no normative value.

With the removal of weeds, soil becomes constantly exposed to sun and rain. Tilling the soil improves drainage, yet further exacerbates the vicious cycle of soil erosion. This is because tilling exposes hidden organic matter to air and sunshine, accelerating its oxidation. At the same time, pruning and harvest reduce the supply of organic matter and hence the supply of ingredients. Without the connections offered by soil aggregates, soil compacts easily, and farmers till the land more frequently… To keep the soil productive, farmers use mulch to cover the soil, and increase organic content by adding fertilizers and soil conditioners like manure and peanut meal.

Agriculture in Hong Kong in the early 20th century relied on these methods. In rural areas, villagers collected manure by themselves. In urban areas, the government established manure stations to collect human excrement (known as nightsoil). Upon treatment, this was transported to fields in the New Territories for use as fertilizer. Vegetables and rice grown in this manner were sold back to urban dwellers for consumption. This mutual exchange of resources between urban and rural areas was only disrupted in the late 1960’s.

With technological advancement, we increased the productivity of soil. Yet this has also brought many side effects. With the end of World War II came the “Green Revolution”, and petroleum-based pesticides and fertilizers became the order of the day. Many Hong Kong farmers came to favour use of chemical fertilizer over manure. This marked the shift from traditional agriculture to conventional agriculture. Chemical fertilizer is highly soluble and efficient. But as it fails to supplement organic matter, prolonged reliance reduces the soil organic matter content to as low as 2%. At the same time, manure became characterized as refuse rather than a resource. This shift in farming methods also had repercussions for the livestock industry. As manure came to be seen as waste, chicken and pig pens were no longer designed to collect manure. Instead, manure was an unwanted byproduct, to be disposed of as quickly and as cheaply as possible. Often, this meant disposal into the nearest river – which is why the Shing Mun River and Lam Tsuen River became so heavily polluted that only extremely hardy fish such as catfish and carp could survive. The Kam Tin River continues to be severely polluted to this day. In the 80’s, the government sought to control the damage by promoting organic farming, and there are over a hundred organic farms in Hong Kong today. The irony is that while organic farmers buy Dutch chicken manure and other organic fertilizers from halfway around the world, manure from 3 million local chickens is dumped into landfills.


Amidst burgeoning New Towns and small houses, we still have 4,000 hectares of agricultural land – although over 80% is abandoned. Brownfields suffer a worse fate, and end up covered in construction waste, oil and toxic electronic waste. In recent years, calls for revitalizing agriculture have become more popular. Yet we cannot simply take the approach of increasing productivity, lest we make the same mistakes as those of the Green Revolution. It is precisely because we have forgotten the story of soil that we now have problems such as excess kitchen waste, fly-tipping and brownfields.

Even if we revitalize agriculture, we should be careful how we grow. Agriculture in itself is the practice of intervening in nature to collect food. Growing methods range from natural farming, in which no fertilizer is used, to hydroponics, where no soil is used. What sets them – and everything in between – apart is how we choose to treat the soil. Do we respect it and cooperate with it, or do we try to control it? History has told us time and again that the attempt to conquer nature can backfire within the same generation.

Returning organic matter from the city, such as kitchen waste, to the land does more than help to grow good food. There is actually more carbon contained in soil than in the atmosphere and land organisms. In the Paris Climate Change Conference early last year, the French government put forward the 4 per 1000 initiative. Increasing organic matter in the soil by 4/1000 every year not only aids food production, but also helps control release of carbon dioxide into the atmosphere by carbon sequestration in soil. As it turns out, while heads of state and diplomats quibble over carbon emissions, only to come up with compromises that are easily repealed by the next incumbent, it is in the hands of each city and each community to use our own soils to control the situation. We cannot distance ourselves by saying that Hong Kong is a financial city – our lifestyle consumes the resources of 3.9 planets combined. Steps have to be taken – if not for the next generation, then for our own remaining years on this planet.

(Author’s note: Thanks to Professor Chau Kwai Cheong from the Department of Geography and Resource Management, CUHK, for inspiring students that soil is not dirt.)

2 thoughts on “DO WE KNOW OUR SOIL?

  1. Hi, I’m a french reader of Gogreenhk, your article is very interesting about the importance of microorganisms and oraganic matter. When I studied landscaping, my teacher explained that 96% of the surface water (rivers, lakes …) and 61% of the groundwater contain traces of pesticides in France. This is the legacy of the “Green Revolution”, pollution and soil leached without humus. It’s time to react.

  2. This is very interesting, let’s hope the regenerative movement of localisation & sustainability burgeons in the coming years as we take responsibility for what we are doing to the earth.

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