Soil: dependence

how society depends on soil

By Dr J Floor Anthoni (2000)
The cultivation of soil has enabled humans to build empires and to progress to what we are today. But the world's population is now increasing so rapidly that within 40 years, enough food and energy needs to be found to accommodate nearly twice the number of people living today. Optimism of twenty years ago has turned into concern. Will we be able to make it? Here are some issues that will sharpen your mind.
history From hunter-gatherer to the modern agro-economic society, has taken thousands of years but now humankind is faced with a very sudden increase in its population, demanding new and smarter methods to sustain it. Humans depend on soil and what it produces, for food, energy and miscellaneous materials.
concern The initial optimism that heralded the green revolution, promising almost unlimited production by applying science, technology and energy, has dwindled in the wake of many failures and few successes.
food requirements One third of the world's population is either undernourished because not enough food is available, or overweight because food is plentiful. A separate section will be devoted to proper feeding, but here is an introduction to our basic needs. 
meat or vegetarian? One way to relieve food shortages is to eat less meat, because in rearing the animals for meat production, energy is wasted. Is this so and would it help?
why need soil? Isn't soil just a substance for roots to hold onto and can't we just do away with it as in hydroponics?
sustainability Soil forms very slowly over a period of tens of thousands of years, too slow to be noticed, reason why ancient agriculture has erased itself in many places. Unlike any other form of economic activity, agriculture must satisfy several criteria of sustainability in order to survive.

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Human populationAs can be seen from the diagram, the human race has grown very suddenly at an enormously accelerating rate after the year 1850 when the industrial revolution began. Before it, the human population curve stayed steady at 500 million people since year zero, with a few dips caused by plagues. From 10,000 years ago, there have been several rapid increases, each co-inciding with an invention of some kind. The number of births and deaths per 1000 population stayed close to 40. But since the 1850s, the death rate declined suddenly, and even more steeply since 1950. The gap between births and deaths has led to the rapid increase in world population. Since about 1950 the birth rate had been declining suddenly but not as fast as the decline in deaths.

Before 8000BC, there must have been some 5 million people in the entire world, just at the end of the first stone age and the beginning of the new stone age, which brought the very first beginnings of agriculture. Before that, humans had to forage and gather food by walking long distances. This kind of life could sustain a family of ten on an area of ten square km. Large aggregations of people were simply not possible.

MordilloEven while foraging, people did influence their environment by removing noxious or useless plant species and helping advantageous ones. This meddling with nature, eventually led to agriculture.
Agriculture went through pastoralism, by which herds of grazing animals were herded over natural pastures, to shifting-farming and finally to traditional farming. Farming required people to stay in one place and farm the earth there, now and then supplemented by hunting and fishing. The new ways of farming, made possible by the invention of the plough and domesticated animals for ploughing and transport, also enabled the development of better tools and weapons from metals. Industry, boats and trade developed.

From 3000BC to 2000BC was the bronze age, followed by the iron age to about 500AD. During that time several civilisations rose and fell, like Babylon, Egypt, Greece, Rome. Although scientists today differ about the causes of the rise and fall of these civilisations, Plato clearly identified the demise of the Greek power from loss of the land, not being able to sustain its civilisation any longer:

"The consequence is, that in comparison of what [Attica, central Greece] then was, there are remaining only the bones of the wasted body, as they may be called, as in the case of small islands, all richer and softer parts of the soil having fallen away, and the mere skeleton of the land being left". Plato, 360BC.
In the middle ages that followed, major inventions were made, that eventually led to the green revolution of today. Although medical technology enabled people to live longer, it was farming and the use of soil for production, that enabled human societies to become denser. Here is a summary of the revolutions in food collecting. Note that hunting and fishing always supplemented nutrition, but those who mastered agriculture, also amassed wealth and power, leaving hunter-gatherer-fisher societies far behind. The question mark in the last sentence indicates that we've reached an era of uncertainty. We will not be able to improve farming tenfold again, because we are reaching the limits of agricultural production in many ways. The question has now become whether  the world population can be constrained and whether we can produce enough food just in time. Also whether the future situation can be maintained sustainably. Most of this section on soil will be devoted to understanding our limits.
The way an ecosystem reacts to a population exceeding its limits, is by rather sudden collapse. As the green curve in above diagram shows, it is quite possible for the world's population to collapse and probably much more rapidly than shown. The brown curve for area of cropland, may collapse too. Most ecologists now agree that without the help of fossil fuel, the world cannot sustain more than half today's population.

The connection between agriculture and civilisation is not a trivial one. In order to be able to maintain a bureaucracy, an army, a legislature (the law), engineers, artisans, and so on, the farmers must produce not only enough food for themselves, but also enough to spare for those  who do not produce their own. The more efficient farming, the richer and stronger is society. This has unfortunately, over the ages, also depressed farm wages, for the less one needs to pay for food, the more is left over to spend on culture. When farmers are put under unnecessary strain, they will farm to survive, taking ecological shortcuts that will inevitably lead to ecological disaster. It is society's responsibility to avoid this happening. Society would indeed be foolish in not assisting its farming communities.

Ironically, on the scale of farming success, the extremes on either end are hard to control: at the lower end, subsistence farming  will exceed nature's carrying capacity in order to survive. Farming for greed at the other end of the scale, will have the resources and the motivation to exceed nature's carrying capacity for short-term profits. In the middle, where farming is just profitable, will it be possible to farm sustainably.


Reasons for concern

In the population growth diagram above, a solid brown curve is also shown, representing the amount of crop land (excluding forest and pasture), increasing from 0.8 to 1.6 billion hectare (Gha) in the time span of 100 years. It is obvious that this curve is flattening off, not keeping pace at all with population. It not only shows how much has been achieved in improving agricultural productivity, but also that no more land is available to increase production. In fact, much good agricultural land has been lost to optimistic farming practices (overfertilising, irrigation, desertification, soil loss), while large corporations appear in control of seeds, fertiliser and pesticides. The world's cropland now stands at 1.5 Gha, after losing 0.43 Gha already, and reaching its limits. By comparison, the surface area of all ice-free land = 13.3Gha; the whole world 51Gha.
The green revolution:

+  Uses less arable land
+  Uses high yield crops
-   Abandons other varieties
-   Reduces biological diversity
-   Needs more soil management
-   Needs more fertilising
-   Needs more spraying
-   Seeds controlled by large corporations
-   High risk of environmental damage

As can be deduced from the summary of advantages and disadvantages of the green revolution, it is not at all certain that it is sustainable and that it will deliver what is needed for 11 billion people. For instance, the amount of cereals (wheat, rice, etc.) per person has not increased since 1975, staying steady (even decreasing) at 350 kg/yr each, despite the fact that grain yields have been increasing from 1.5 tonne/ha to 2.5 in the same period. Simply by more people having to share the same land, the available cropland per capita was 0.3 ha in 1986 and is now 0.23 ha, decreasing further to 0.15 ha by 2050. It is estimated that 0.5 ha per person will just give an adequate amount of food and cooking fuel (Americans have 0.68 ha each). Not knowing that the world's arable soils would become so scarce, people have built their cities over the most valuable and productive soils. In the USA 0.8 ha per person has been paved by cities and roads.

To compound the situation, due to our increasing affluence, more soil is needed for: water collection, stock fodder, domestic fuel, paper, energy farming (windmills, trees, etc.), rubber, wine, beer, coffee, tea and so on.

Modern agriculture is characterised by large industrialised monocultures. Where pigs or broilers (young chickens) are reared, they are reared in closed confinement in very large numbers, producing large amounts of wastes that are difficult to recycle because of transport costs. Large fields in monoculture are very sensitive to pests, requiring excessive amounts of chemical pesticides. There's little scope for land cycling (alternating crops), green manuring (alternating fertility crops like legumes) and fallowing (leaving land unused). To reach the highest possible yields (and profit), even small losses to birds, mice, insects, are fought with chemical overkill. Pesticides and fertiliser leach into groundwater and aquifers and into streams and the ocean, where they cause measurable harm. A safe limit of 50ppm (parts per million) nitrate is in place for our aquifers, but this amount kills marine fish and other organisms in a marine aquarium. In many cropland areas, such as in Holland, groundwater is polluted by concentrations of nitrates exceeding 100ppm. The amount of nitrate raining down from the sky, in many places in Europe and the USA, exceeds the equivalent of 100kg/ha fertiliser application. It fertilises dunes and changes their ecology.

For optimal productivity, farm animals are fed growth hormones and antibiotics, which end up in their meat, causing endocrine disruption in people who eat a lot of it (excessive growth, obesity and early start of menstruation in girls are known to have been caused by better diets, but may be linked to the use of hormones in food as well).

Although much environmental harm has been caused already, the good news is that both consumers and farmers are becoming more aware and more cautious in embracing new technologies for profit only. We are obviously entering an era where we need to be smarter and eat smarter.

Food requirements

Of the 6 billion people on Earth, 1 billion is seriously underfed, suffering reduced life spans, whereas an equal number is overfed, also reducing their life expectancies considerably. The human body is capable of  surviving happily somewhere in between these extremes. The ability of our fat cells to store fat for times of need, has served us well in the course of evolution, but since food has become so readily available in fast food outlets and elsewhere, many people fall victim to the seduction of eating too much and too much fat. How we spend our energy, and how to eat will be treated in its own section, but here we'll look at the ecological aspects.

The main food components people need are (with daily pure amounts per kg body weight):

Plants can provide all of the above, making life as a vegetarian perfectly possible, although with some difficulty. Particularly children under 3 years, need animal proteins (milk, eggs, 2g/kg/day). A problem with protein is that mammals, including humans, are unable to make 9 essential amino acids (and one more very early in life). Although animal meat provides these in the right ratios, plant proteins usually do not. It requires vegetarians to eat more plant protein than the required daily amount (RDA).
Typical energy expenditures (approximately):
500kcal - 8 hours sleep (Basal Metabolic Rate BMR is 1500 kcal/day)
750kcal - 8 hour office job (1.5 x BMR)
1200kcal - 8 hour medium job, gardening, teaching, (2.4 x BMR)
2000kcal - 8 hours tree cutting, digging (4 x BMR)
3000kcal - 8 hours truck loading, pit sawing (6 x BMR)
1500kcal - 1 kg potatoes, 0.5 kg meat, 100 g plant oil.
As can be seen from the above range in energy expenditures, the amount of food needed also varies. It would indeed be very difficult or impossible to predict the amount of food needed to feed the world, by starting from these figures. The best estimate we can make, is by starting from the situation as it is today, taking account of a doubled population and 50 percent extra for more equality in the distribution of wealth. It adds up to being able to provide 3 times more than today, which, as we will see, is not achieved easily and sustainably.

From the amount of energy spent in an office job, it is difficult to compose a diet that does not overfeed, yet provides everything one needs. A few greasy chips, a bar of chocolate and similar delights, can easily tip the scale, resulting in preventable disease. The more energy one spends, the easier it is to eat healthily. It is not surprising then, that many diseases are linked to poor eating habits, or rather poor exercising habits, diseases that were uncommon before the automobile became commonplace:

Health problems that could be avoided by diet change and exercise
disease or condition % of cases
what to do
cancer 30-40 eat more fruits and vegetables, less fat and exercise more
coronary heart disease 17-25 eat less fat and exercise more
childhood blindness 25-50 eat more vitamin A; more vegetables rich in micro-nutrients
mental retardation 33-43 use iodised salt.
adult-onset diabetes 64-74 eat less fat and exercise more.

the above shows that one cannot be healthy without exercise!

Meat or vegetarian?

The food/energy pyramidAgriculture does not escape the principles of physics and ecology. One of these is the food or energy pyramid, shown here. Solar energy is converted by grass (primary producer) and is eaten by grazers (primary consumers). They use the food for growing , moving and living. But only a small amount is used for growing, usually between 5 and 20%. It is called the conversion efficiency or conversion rate. For quick ecological estimates, often the figure 10 is used, meaning that 10kg food is required to grow one kg. It corresponds to 10% efficiency.
If wheat was grown instead of grass, humans could eat the wheat direct, and thus attain a ten times better usage of the soil. So if people went vegetarian, we would get up to ten times more food, solving the world's food shortage in one step. We will see that this is not that simple.

Kleiber's line, metabolic rateIn studying how animals spend their energy, Kleiber discovered that there is a fixed relationship between body weight and basal metabolic rate, the energy spent when at rest. In mammals, this energy is mainly used for staying warm, but part of it also for breathing and pumping the blood round. It is known that the weight of an animal is related to its length to the power of three and its surface area likewise to the power of two. So, bigger animals need to spend more energy to stay warm, but proportionally less than small ones. A human baby spends proportionally more energy staying warm, than an adult. If heat loss were the only expenditure, Kleiber's law should be:

BMR = 3.4 x weight 0.67  rather than BMR = 3.4 x weight 0.75 , but this is a fine detail.

It is important to know that some farm animals spend more of their energy growing than living, and pigs and broilers appear to be very effective at gaining body mass, particularly when young. Like humans, mature animals no longer grow. They spend their energies in living and reproducing instead. If one wants to rear lots of young animals for the production of meat, it can only be a species that reproduces profusely, like pigs (1-15 per litter, 3 litters/year), chickens (200-300 eggs/ year), rabbits (?). The traditional grassland animals like cattle, sheep, goat, deer are most unsuitable.

Kept in confinement, animals will, out of necessity, spend little energy in moving around. So the conversion rates are optimal. When also fed the right diet, their conversion rates can be astounding:
Piglets are weaned after 3-5 weeks, reach slaughter weights of 90-100 kg in 100-160 days. It means that many pigs are now marketed in less than 5 months after birth. Weaned piglets start with a conversion rate of 1.3, rising to 3.5 at 90 kg body weight.
Chicken broilers do even better, perhaps because of their higher body temperature and being non-mammals. In 9 weeks they reach 2-3 kg for conversion rates starting at 1.5 and ending at 2.0. (Ducks 2.5-2.9 and turkeys 2.5-3.2).
Compare these conversion rates with cattle (8-19), eggs (2-3), fish (1.4-2), milk (1.0). The table below , compares efficiencies of animal food production:

Efficiencies of animal food production
milk eggs chicken pork beef carp salmon
conversion rate kg/kg
edible weight % (EW)
effective conversion rate
protein content %EW
energy content kcal/kg
(*) per litre of milk. Multiply by 4 to compare with other columns.
After Vaclav Smil: Feeding the world. 2000.

From this table we can see that food production from milk, eggs, chicken and pork is far more efficient than from grazing animals like sheep and cattle, but fish are most productive. In Asia and china, fish aquaculture in freshwater ponds has almost reached the same volume as all ocean fisheries, supplying well over 15% of all dietary protein. Carp ponds can produce 100-300kg/ha (50kg/ha protein) without any fertilisation or feeding, but with extra feeding, polycultures of multiple fish species yield 15-40t/ha. Compare this with 80t/ha for  vegetables and 20-30t/ha for fruits, all yielding much less protein per ha.

Polyculture of freshwater fish species
Silver carp (Hypophthalmichthys molitrix) lives near the surface, feeding on phytoplankton.
Bighead carp (Aristichthys nobilis) occupies the middle layers, feeding omnivorously on plankton.
Grass carp (Ctenopharyngodon idella) is a herbivore, feeding on aquatic plants and organic waste.
Common carp (Cyprinus carpio) lives on the bottom and feeds from detritus.

Chinese aquaculture finfish
Source: Vaclav Smil: Feeding the world. 2000.

With milk, eggs, chicken and pork being such efficient protein converters, the world would not be helped very much by exclusively vegetarian diets. Besides, much of their food is considered unsuitable for humans, such as fish meal made from by-catches, and crop wastes. Whereas fish ponds and milk cows may compete with good cropland, beef cattle and sheep roam on grasslands that are not suitable for cropping, so they remain efficient sources of meat, hides and wool. So, neither cropland nor harvest can be saved by shifting our appetites to vegetable matter.

Why do we need soil?

Why need soil?Why would we need soil in the first place? Can't we rely more on using hydroponics to feed the world? Hydroponic cultivation is the pinnacle of technological cropping, where most of the climatic conditions are controlled: temperature, CO2 concentration, moisture, nutrient levels. Usually done in temperate climates inside modern glasshouses, this method of high intensity cropping has found widespread use. 
In the glasshouse the temperature is kept under control. Often carbon dioxide gas is added to the atmosphere inside. Chemical sprays can easily be contained inside a closed environment, resulting in savings. But best of all is the controlled application of nutrients, while water is copiously available because it is circulated. 

Hydroponics has taken the world by storm for the cultivation of specialty crops such as high quality and highly priced vegetables and fruits. Hydroponic cultivation requires a flat, slightly sloping floor and a capital-intensive structure. In most cases the energy content of the product is less than the energy put into the process. It is energy inefficient and unsuitable for the staple food of the world like cereals, tubers and pulses (beans), or for slow growing crops like tea or rubber. But it has proved that soil is not strictly needed for growing food. So what advantages does cropping in the open soil offer?

The idea of agriculture is to convert solar energy into food and products necessary for people, with the least amount of meddling (time, energy, fertiliser, chemicals). It ought to be like using the forces of nature to produce what we need. Since the only living organisms able to convert sunlight into something useful, are plants, agriculture will mainly be concerned with growing plants. Over the eons of time, plants and soil have been together, the one influencing the other. They form the most important part of the terrestrial ecosystem. Soils do naturally what has to be done artificially in hydroponics, like:

By understanding how soil works, we will be able to farm in an ecologically friendly way that will be sustainable forever.

Unlike any other economic activity or commercial business, farming must satisfy a number of harsh sustainability criteria. It also operates under high external risks and uncertainty (weather, disaster). For society's own sake, and in order to enable farming to become more productive, some help is needed to insure risk, provide capital and to look after the precious and vulnerable resource, the soil. Society does not know of any asset that is (or should be) as long-lived as soil. Which building, bridge, dam will have a life of over 10,000 years? How much is soil worth? How much would it cost to make a hectare of soil by artificial means? We don't know the answer. Is it important? How important is food? What comes first, fuel or food? Hypothetical questions perhaps, but they dig at the roots of our attitude to soil and agriculture. It requires us to think outside the frame, outside present economic thinking.
Agricultural sustainability
  • be profitable
  • be energy efficient
  • retain soil quantity
  • improve soil quality
  • retain water quality

Before everything else, farming, like any other business, needs to be profitable in order to survive. That means that dollars earned must exceed dollars spent. Unlike most other businesses, farming operates under the vagaries of weather and climate. Unlike most other open air businesses, farms are hit hard by natural disasters, from frost and deluge to earthquakes. These are unpredictable and hit hard at a community's resilience, their damage erasing many years of profits. Farmers are extremely exposed to fluctuating and usually unfavourable market prices. In small markets, these are unduly influenced and controlled by the big buyers, resulting in underpayment for their produce. The farm cycle is controlled by the seasons, leaving little room for planning, marketing and stockpiling. Farmers live in remote areas, incurring high costs for their daily needs and the education of their children. The list goes on.

Farmers derive their resilience from nature's ability to repair, from being able to postpone costs a few years. But loan repayments do not fit into this category, hence their need for assistance in financing.
Above all else, farmers need to look after the soil that enables them to live, a soil 'borrowed from our children', a soil that must be bequeathed to them 'in as good or better state as we received'. With a renewal rate of tens of thousands of years and erosion risks far too high, this is no easy assignment.

The American Society of Agronomy defined agricultural sustainability as summarised in the box on right. They go as far as saying that it should enhance environmental quality, the resource (soil) and the quality of life for all (not just the farmer), an even tougher mission. Mr Rutan has added another constraint, that of substituting biological technology for chemical technology. (Is any farmer reading this?)


Agricultural Sustainability:
  • Enhances environmental quality 
  • Enhances the agricultural resource base
  • Provides for all our food & fiber needs
  • Is economically viable
  • Enhances the quality of life for all
AND while improving plants, animals and production practices, facilitates the substitution of biological technology for chemical technology. (organic farming principles) [V W Rutan, 1989]
Large-scale farming is constrained too by having to be energy-efficient, which means that the amount of energy used must always be less than the amount of energy in the product. Many businesses exist, indeed the majority, where this is not true (all services, the bureaucracy, army, police and so on). Farmers use their tractor, which cost energy to make and fuel to run. They use fertilisers made or modified by factories and transported to the field. They use chemicals that were produced with large amounts of energy from fossil fuel. The list goes on.
As fossil fuel becomes more expensive, the drive behind farming efficiency using high yielding crops, will bend towards higher fuel efficiency (less fertiliser, chemicals, tilling, transport). So the question becomes 'how little fuel?' rather than 'how much yield?'.

Most of the chapters in this section on soil will focus on its sustainable use, and the understanding necessary to do so.

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