Topic of Book
The Pimentels explore the relationship between food, energy and society.
While about half of this book is about managing modern agriculture, the first half gives an excellent introduction between the relationship between food, energy and society. The book is particularly strong about collecting the amount of energy produced from each crop and technique.
- Food and energy are critical resources for humans and all other animals.
- In prehistoric times, 95% of total energy expended was used for food.
- In the wealthiest societies today, this level has dropped to 15-30%.
- All food power ultimately comes from the sun, but plants can only convert 0.1% of that sunlight into biomass. And the vast majority of that biomass is inedible for humans.
- 90% of the world’s food supply comes from only 15 species of crop plants and 8 species of livestock.
- Cereal grains, particularly wheat, rice and corn, have been the dominant food source for millennia.
- In agricultural societies, virtually all people worked in the fields to grow food for society and a tiny elite who worked elsewhere.
- Animal power, particularly horses, oxen and water buffalo, has been used to supplement human muscle power.
Important Quotes from Book
In natural communities, the entire structure and function of the population revolves around food as an energy source. This situation is also true of human societies
The major reason why food and energy are considered critical resources for all natural communities, including humans, is that living plants can convert relatively limited amounts of solar energy—only about 0.1% of the sunlight reaching the Earth—into biomass. Before fossil fuels were discovered and used, humans shared with other animals that portion of the sun’s energy captured by plants and subsequently converted to food/energy.
One measure of the relative importance of food in society as a whole is the amount of energy and labor devoted to producing it. In prehistoric times, about 95% of the total energy expended by the family was used for food. This included hunting and gathering, transporting the food back to camp, and preparing it for consumption. Even today in some developing countries, the energy expended on food systems represents 60–80% of the total expended. By contrast, in many developed countries the proportion of energy devoted to food production ranges from 15% to 30%, and little of this is human energy.
Energy is defined as the capacity to do work… Light energy coming from the sun is the most important and universal type of energy, supporting all life on Earth.
The survival of humans in their ecosystem depends upon the efficiency of green plants as energy converters. Plants convert sunlight into food energy for themselves and other organisms. The total foundation of life rests on plants’ unique capacity to change radiated solar energy into stored chemical energy that is biologically useful for humans and other animals.
Most plants divert significant proportions—from 5% to 50%—of the energy they collect into their fruits and seeds, illustrating the high priority plants give to reproduction.
Natural ecosystems, of which humans are a part, are fundamentally a network of solar energy and mineral flows. Green plants capture solar energy and convert it into chemical energy for use by themselves and the remainder of the biological system using the elements of carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and others. The food supplied by plants in the ecosystem is basic to the survival of all animals, including humans. It is the foundation of the entire life system. Some of the solar energy plants convert into stored chemical energy is passed on to herbivores and parasitic microbes.
Since the first organisms appeared on Earth several billion years ago, many basic trends in the evolution of living systems have been apparent. First, the living system has become more complex, with an ever-growing number of species.
Water, followed by nutrients, is the principal limiting factor for terrestrial plant productivity, including agriculture.
After water, soil nutrients (nitrogen, phosphorus, potassium, and calcium) are the most important factors limiting crop productivity. Valuable nutrient resources available for recycling include crop residues and livestock manure.
At present, 90% of the world’s food supply comes from only 15 species of crop plants and 8 species of livestock. This is a very narrow base, especially considering that there are about 10 million species of plants and animals in the world today.
All operations required in agriculture can be carried out by human power. However, producing crops by hand requires about 1200 h/ha, and each person can manage only 1 ha during the growing season. Under such production conditions, only the bare minimum of essential human needs can be attained; the amount of the surplus.
Hunter-gatherers probably expend 60–80% of their energy intake in securing food. In fact, obtaining food and collecting firewood for its preparation usually dominate the activities of these societies.
Gradually, aided by this improved mode of transportation, trade between villages developed. As early as 2500 b.c., cattle, including oxen and water buffalo, were used to transport people and goods and to draw plows (Leonard, 1973). The use of animal power to cultivate the soil was an immense breakthrough in agricultural production. Tremendous quantities of energy and about 400 h of heavy labor were expended when humans worked alone to turn 1 ha of soil for planting. With 1 h of ox power substituting for 3–5 h of human power, the time and energy requirement was drastically reduced. About 3000 b.c., the invention of the wheel made possible a tremendous increase in the efficiency of transportation . The wheel doubled the load of goods that could be transported per unit of energy.
In addition, the wheel led to improved efficiency in other food-related processes, such as grinding cereals.
Almost 90% of the plant calories/ protein consumed by humans comes from 15 major crops rice, wheat, corn, sorghum, millet, rye, barley, cassava, sweet potato, potato, coconut, banana, common bean, soybean, and peanut.
Cereal grains have always been the dominant source of human food for several reasons. Cereals can be cultured under a wide range of environmental conditions e.g., soil types, moisture levels, and temperatures), and they yield large quantities of nutrients per unit of land area. In addition, cereals have a relatively low moisture content (13%–15%) at harvest and can be transported more efficiently than potatoes, cassava, and other vegetables, which are about 80% water. The low moisture content of cereals facilitates storage for long periods of time with minimal storage facilities. Finally, most cereal grains sustain only minor damage from pests.
The prime disadvantage of cereal grains is that they contain low levels of lysine, an essential amino acid. Also, dry cereal grains average only about 9% protein, whereas dry legumes average about 20% protein. Most legumes are low in the essential amino acid methionine but high in lysine. Therefore, by eating combinations of cereals and legumes, humans can obtain sufficient quantities of the essential amino acids. In fact, grains and legumes have long been staple foods for people in many areas of the world.
Corn Production in Teposlan, Mexico (axe and hoe; human power only)
1144 hours labor
Yields 6.9 million kcal/hectare
Corn Production in Guatemala Mexico (axe and hoe; human power only)
1414 hours labor
Yields 3.8 million kcal/hectare
Corn Production in Teposlan, Mexico (using oxen)
383 hours labor
Yields 3.3 million kcal/hectare
Corn Production in Guatemala (using oxen)
700 hours labor
Yields 3.7 million kcal/hectare
Wheat Production in Uttar Pradesh, India (using bullocks; castrated bull)
615 hours labor
Yields 2.7 million kcal/hectare
Rice Production in Iban, Borneo (axe and hoe; human power only)
1186 hours labor
Yields 7.3 million kcal/hectare
Sorghum Production in Sudan (hoe; human power only)
240 hours labor
Yields 2.9 million kcal/hectare
Cassava Production in Tanga, Tanzania (hoe; human power only)
1284 hours labor
Yields 19.2 million kcal/hectare
- “The Agricultural Systems of the World: An Evolutionary Approach” by David Grigg
- “An Introduction to Agricultural Geography” by David Grigg
- “Alchemy of Air: … the Scientific Discovery that Fed the World” by Thomas Hager
- “A History of World Agriculture” by Mazoyer and Roudart
- “First Farmers” by David Bellwood
- “People, Plants and Genes: the Story of Crops and Humanity” by Denis Murphy