Lecture 21

Notes on Lecture 21

Despite a long history of predicting that the human population will reach its carrying capacity in the early 21st century, human population continues to rise. However, concerns about the sustainability of this population increase force us to think about how natural and human systems are coupled. Agriculture is one area where these two systems are intimately linked and thus, deserves greater analysis.

Types of Food Procurement
-Hunting and gathering from wild stocks
-Cultivation of domesticated plant crops
-Pastoralism: humans follow animals as they range over an area of land
-Animal feeding: Animal feeding refers to providing animals feed that could be consumed by humans e.g. corn. Whereas pastoralism entails animals consuming wild foods that are not food sources of humans or are not digestable by humans.

History of Agriculture

Neolithic Revolution
The dividing line between the Old Stone Age, which was dominated by nomadic hunting-gathering, and the New Stone Age, which saw the initiation of animal and plant domestication and a progressive abandonment of nomadism, occurred roughly 10,000 YBP. It is unclear how long the domestication process took for various species, but one hypothesis is that the domestication of plants happened at midden (trash) sites. Humans selected plant species from the wild and discarded the seeds and other food wastes in communal midden piles. These seeds germinated and if bearing a desirable food source, were further selected by humans. Over time, the idea of planting seeds may have emerged from observation of how seeds in midden piles grew.

It is unclear whether animals or plants were first domesticated, but we do know that domestication occurred in multiple sites (China, Peru, Mesopotamia, New Guinea) between 10,000 YPB and 5,000YPB. What drove this process? Some combination of poopulation pressures and extinction of wild game and foraging species encourage the domestication in areas where suitable plant and animal stock already existed. These centers of domestication were initially separated, but millenia later, cultural practices, technology, and plant and animal stocks began to diffuse/be traded.

Early agriculture was primarily swidden agriculture, in which tracks of forests are cleared, usually by fire, and desired crops are planted in the ashes. After a certain period of time (usually two years in the tropics), the plot is abandoned , and new parcel of forest is cleared. The process is then repeated. The forest reclaims by succession the first plot and after a certain fallow (rest) time has passed, the original plot may be cleared again. The need to abandon the plot differs but in the tropics, it is either because of weed competition or from nutrient exhaustion of poor soils. Trees established in the fallow period replenish soil nutrients and limit soil erosion and may themselves be used by humans (fruit, timber, medicine,etc.)

Agricultural Systems

Such systems consist of the crops and animals, inputs (both material and labor), and timing and spacing of activities. Farmers may choose to grow monocultures or mixtures of different crop species. They may rotate different crops over a specific plot of land, planting a different monoculture of species in each plot each year. Crop rotations limit the buildup of pest and pathogens, facilitate nutrient recycling, an d improve soil structure. Farmers also have a wide choice of inputs such a manure, dung, straw, compost, seaweed, and irrigated water. In what seasons crops are grown and what types of crops, how long the land is in cultivation, and how long it is in fallow are all variables that are important in defining a particular agricultural system. These decisions may also determine whether the human settlement associated with the cultivated land are sedentary or shift over time. The extent and placement of animals are additional factors for consideration in an agricultural system.

Example: In-field/Out-field System

In this system, land is divided into an in-field, a series of cultivated fields close to the human settlement, and an out-field, an area of pastures and forest in which animals graze during the day. At night, the animals return to the infield where they are penned and their manure contributes nutrients to the soil. Plots within the infield undergo crop rotations plus usually a fallow period.

Shifting Cultivation

During fallow periods, other products may be harvested (timber, medicine, fruits). It is an agricultural system in which plots of land are cultivated temporarily, then abandoned. This system often involves clearing of a piece of land followed by several years of wood harvesting or farming, until the soil loses fertility. Once the land becomes inadequate for crop production, it is left to be reclaimed by natural vegetation, or sometimes converted to a different long-term cyclical farming practice. Andecological consequences are often deleterious, but can be partially mitigated if new forests are not invaded. Of these cultivators, many use a practice of slash-and-burn as one element of their farming cycle. Others employ land clearing without any burning, and some cultivators are purely migratory and do not use any cyclical method on a given plot. Sometimes no slashing at all is needed where regrowth is purely of grasses, an outcome not uncommon when soils are near exhaustion and need to lie fallow. (Wikipedia)

Mechanization Revolution

Mechanization of agriculture in the 19th century in Europe and the United States dramatically improved farmer efficiency, reduced the need for rural labor, and facilitated the Industrial revolution by enabling the movement of people to urban areas. New technologies increased the area of land under cultivation. For example, the steel plough was able to turn over tough prairie sod and opened the way for the grain belts of the Midwest. Initially, mechanization was animal-powered, but the invention of the gasoline-powered tractor fed by cheap petroleum remade the farm. Draft animals were no longer necessary, allowing for the conversion of pasture into fields, and the smaller footprint of a tractor allowed for crops such as corn to be planted closer together in rows.

Intensification v. Extensification

Intensification involved increasing the productivity per unit of land or per capita of participent. Extensification involves increasing the land or the labor involved in agriculture, but not the productivity per unit of land or per capita of labor. Both are means to increasing the total yield in an agricultural region. Intensification is usually achieved via: 1) irrigation 2)inputs such as fertilizer or manure, 3)more energy (animal or industrial), 4) differennt types of labor or intensity of labor e.g. weeding, and 5) greater flows of capital and technology. Intensification only makes sense when land tenure is defined, the area under production is secure and safe, and markets for extra production have been developed.

Green Revolution 1.0

From the 1940s to the 1970s, farmers in the first world embraced a package of agricultural elements that dramatically increased per acre yields by on average 2.6 fold. This package consisted of machines, crop breeding , and chemical pesticides, antibiotics, and fertilizers. Mechanization accelerated during this period with gas-fueled equipment replacing virtually all animal-power on farms. New hybrid varieties of crop were bred to be drough and disease resistant, but also plant architecture was changed to allow for stiffer stems to hold heavy seeds heads. Farmers also began to use high levels of chemicals. Antibiotics were fed to animals to cure disease but also to aid in weight gain in healthy animals. Synthetic fertilizers, herbicides, and pesticides were sprayed on fields. Levels of pesticides applied plateaued in the early 1980s, but only after more than a decade of protests.

Green Revolution 2.0

The same suit of technologies began to be exported to the Global South in the late 70s/early 80s, just as first world use of such technologies began to plateau. World use of fertilizers peaked in the early 90s, fell, but is now climbing back to record levels.

Advantages of the Green Revolution

High yielding varieties have allowed food production to keep pace with population growth (so far). The number of people required to grow food has plummeted with the average US farmer producing enough food for 130 people, freeing up labor to enter industry.

Disadvantages of the Green Revolution

A low-input system has been replaced with a high-input system that dramatically increases our reliance on petroleum, fertilizers, and pesticides. These inputs often leak from farm land, causing eutrophication and dead zones. Roughly 220,00 people, often quite poor, are poisoned and killed by pesticides each year. Both petroleum and groundwater are non-renewable resources that will be depleted within the next century. Such a system is inherently unsustainable.

Major Issues:

-Hunger and equity: People starve not because of food shortages, but because they cannot afford to purchase food…
-Continued deforestation: How to feed more people without land use/land cover change?
-Continued intensification?
-Corporate farming, corporate control: Should large corporations control the food supply?
-Biofuels: Can we devote cropland to non-food crops? Will this encourage deforestation?
-Genetic engineering:Much promise, but at what cost?

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