Introduction to agricultural systems


Subsistence Farming and Shifting Cultivation



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Subsistence Farming and Shifting Cultivation. This system is based on food production to meet the needs of a family. Traditionally, it required only a few hours of work per week in labour to produce food and to collect cooking fuel. In modern cash economies, these systems are disappearing. These people now usually produce some cash crops to supplement there needs, as permitted by distance to market and infrastructure development, such as roads to get their produce to a market.

Shifting cultivation is a very old system, and was usually the type of agriculture practised by subsistence farmers. Fields and settlements were moved at intervals as productivity declined over time. Old land was left idle to revegetate for several years in order to restore soil organic matter and nutrient levels in the soil. The length of fallow period and the number of crops prior to the fallow period would vary, depending on soil quality.

The major problem with this system is increasing population in areas of the world where shifting agriculture is practised. If the population density is low, land can be left fallow for 20 to 30 years before it is reused, and in that time fertility levels are restored. If population is too large and food needs increase, the fallow periods are shortened. Land may be used before fertility has been restored by natural cycling processes, or used for longer periods so that soil erosion can become a problem.

Cropping practices vary with location, but usually two or more crops are grown together (intercropping). Intercropping reduces susceptibility to pests and diseases, provides a complete vegetation canopy for maximum photosynthesis and protection of the soil from heavy rainfall and erosion. Animal production is variable. For example, in West Africa the tsetse fly limits cattle production in regions where shifting agriculture is practised. In rainforest areas, generally a few goats, sheep, and chickens are produced to supplement protein intake, whereas in

Latin America, large cattle herds are often part of the system.

Capital and labour requirements of the system are relatively low. Labour is mainly manual work for clearing, land preparation, planting, weeding, harvesting and processing, and occupies about half of the working time. Tending livestock, marketing and collecting water uses the other half of the labourers time. Labour efficiency can be improved with better tools and higher yielding crops, but that may deplete soil fertility more rapidly and increase the fallow period required because nutrient availability is always a major factor limiting productivity in these systems.



In some areas, shifting cultivation systems are threatened by large increases in population. For example, in Thailand refugees from Burma and China have flooded into the northern mountainous zone. The large increase in population and the loss of opium, which is now illegal, as a cash crop, have meant that the stable system of shifting cultivation used by the hill tribe people for thousands of years is now becoming unstable and environmentally damaging. The Thai government is attempting to develop new agricultural systems that combine shifting cultivation practices with partial permanent planting. The government has also protected some sensitive watersheds, which means that they cannot be cultivated. The new systems rely on production of both food and cash crops, with the money from cash crops used to buy fertilizers and pesticides which should decrease nutrient loss from the soil, increase overall productivity and make continued production possible. Many of the new systems are based on agroforestry, in which horticultural crops are inter-planted with fruit, nut and berry trees to provide some permanent cover and reduce erosion and on steeply sloping lands. Although these systems seem to be successful, some of the hill tribe people worry that their new reliance on cash makes them dependent on markets over which they have no control. They have watched input prices increase and produce prices decline over the last ten years. Subsistence shifting agriculture allowed these people to be completely self-sufficient.

Shifting cultivation and pastoral systems are solar energy farming systems - they do not rely on energy subsidies. Although they are not highly productive, these systems are have been sustained for hundreds, maybe thousands of years. Their sustainability is now questionable because of increased population which causes farmers to reduce the fallow period. Reduced fertility is sometimes countered with fertilizer inputs, but that increases the need for capital among farmers who are often poor and remote to have access to markets to raise cash and buy inputs.



Settled Agricultural Systems. The process of adapting cropping patterns and farming practices to the conditions of the land resource and climate has resulted in many distinct types of settled agricultural systems in the Tropics. Some of the major systems will be discussed in this section.

Irrigated Rice cultivation (Goodland et al., 1984, pp. 8-13). Asia produces most of the world's rice, but only a third is irrigated. Irrigated rice landscapes have been recontoured over hundreds of years, with terraces and bunding to provide very sophisticated systems of water control. These practises evolved to improve water availability during growing season. Although they are now often associated with large-scale hydroelectric dams, river flood water was the traditional source of irrigation water.

Paddy rice is often grown on the most productive soils in Asia, where the high use of inputs can be returned in high yields. Traditional rice varieties can be fertilized, but they do not respond as well to high levels of fertilizer. Pesticides may also be used, but traditional varieities usually have fewer pest problems because they are grown as part of a more diverse system, with several varieties of rice and other crops grown together. As part of the traditional wet rice production systems, a N-fixing cyanobacterium (Anabaena azollae) was often grown in symbiotic association with a water fern (Axolla spp.) in the irrigation water of paddy systems to contribute significant amounts of N to paddy soils. (The relationship is like that of the Rhyzobacteria and legumes). The saturated conditions of the rice paddy also increase the availability of P and K to plants.

The infrastructure of irrigated rice production is at least partially commercial and therefore requires access to markets, and a transportation system. New high yielding varieties are often sold in a package that includes credit, extension services, and chemicals.

Dry land or upland rice is also a common crop throughout the Tropics. It is usually grown on sloping lands within intercropping systems with other annual and tree crops.


Tropical dryland farming (Tivy, 1979, p. 202) is common in the African Sahel, South Africa karoo, North and East Australia, north east Brazil and parts of India. It is practised in areas with semi-arid precipitation and high temperatures that result in a high evapotranspiration rate. As a result, there is less effective precipitation than in semi-arid temperate zones; however, temperature is favourable for crops all year round.


Soils are generally more weathered, acidic and leached, resulting in poor soil fertility. That combined with low and variable precipitation limits cropping options. One crop and one grass or bush fallow is a common practice, especially in Africa.

Subsistence staples, such as sorghum and millet are common crops. They may be supplemented with protein crops like cowpeas and groundnuts, or with carbohydrate crops like and cassava which also tolerates low fertility. Goats, sheep, poultry and cattle are kept if grazing is available.

The major problems are increasing population pressure which results in:


  1. reduction of the fallow period

  2. declining soil fertility, and

  3. the cultivation of pasture land, which is usually dry and of low quality, resulting in soil erosion and soil degradation

Dryland systems are also used in tropical Asia, because not all farmers have access to irrigation water for paddy rice, or only a part of the farm produces wet rice. On dry fields, crops such as manioc, yams, maize, groundnuts, soya beans are grown, with hoe or draft animal and plough. Sheep, goats, poultry, oxen, cattle and water buffalo are kept to graze on the stubble. Root crops, vegetables, spices, medicinal herbs, tobacco, citrus, mangoes, coconut palms, coffee, tea, pineapples, papaya and banana are grown for consumption and as cash crops.

These farmers produce food and cash crops, and require infrastructure and markets. Inputs, such as fertilizers, machines, and pesticides are used by the farmers who have money, but not by all farmers. Villages in these areas usually include some landless people, who provide labour and are paid in produce and cash.


Plantations (Manshard, 1974, p. 89) are large-scale agricultural enterprises, producing high value crops, and involving large investments of capital and labour. They began in colonial times by Europeans, and are based on an industrial and export model of agriculture. Plantations were designed for the production of one crop in monoculture, originally using slave labour, but now using a combination of labour and mechanization. Crop sales are made on the world market, and are sensitive to market fluctuations (i.e. sugar, palm oil).

Plantations are managed by either independent owners, in the case of relatively small plantations, or by large corporations (United Fruits) which may own many large plantations. Corporate plantations may also include processing facilities on the site.

Traditionally plantations produce a monoculture crop, but increasingly, complementary crops are produced together. For examples, coffee and papaya in East Africa, oil palm and cocoa in Zaire, coffee, mangoes, avocados and bananas in El Salvador. The move away from monoculture crops reduces the risks associated with production of commodities that can vary widely in price on the world market.

Are plantations good or bad for tropical countries? They use modern farming methods and improved crop varieties, which brings those improvements to countries that could not otherwise afford them, but they also often use of high rate pesticides to increase yields and are thus often a source of potential pollution and health problems for local labourers. Plantations operating on an industrial style with economies of scale reduce costs and processing on the sight increases product quality. They provide employment, infrastructure, sometimes food rations, and foreign currency for the local people.


Summary. Tropical systems were mainly solar energy based systems, that have been sustainable, with low populations, for hundreds of years. Crops and livestock productivity may be low, but they are adapted to local climate and soils conditions and the people are often self-sufficient with little interaction with the cash economy. Productivity versus well-being may not be directly related. Self-sufficient farmers who produce their own food and other needs can be better of than farmers in more highly productive commercial (rubber, coffee etc) systems. Commercial farmers must purchase all of their food and other needs, and are dependant on often fluctuating markets for the money needed to buy food.

Increasing population is a problem, because it causes farmers to increase cropping intensity (try to produce more per ha) which reduces soil fertility and soil quality in general. Chemical, purchased inputs may be required to maintain productivity, which creates a need for capital, farmers must then devote some of their land to production of saleable commodities, further reducing land availability for food production.

3.5 Temperate Agricultural Systems
3.5.1 An overview of the temperate resource base (Strahler, 1974, pp. 250-265; Thorne and Thorne, 1979, p. 23; Vasey, 1992).
Cool Temperate Zone.

This region covers 22% of the total land area and 29% of arable land on earth. It occurs between 35 to 55o N in Europe, Asia, North America and Russia. It is associated with a continental climate with heat during growing season and cold winters. The growing season is limited by spring and fall frost. This zone is dry enough that leaching in minimal, soils are rich in N and OC, but wet enough that grass production is good. It includes several broad vegetation zones.



Humid Zone. There is adequate precipitation (50 to 100 cm) for crop production throughout growing season of 4 to 8 months. The native vegetation is deciduous and mixed forest, although now it is mainly cleared and cropped. Soils are generally acid to neutral with relatively low fertility due to the leaching potential. The amount of available N and SOM in soils declines from north to south as precipitation decreases.

Semi-arid and arid zone. The most extensive areas of this zone occur in central Russia and Northwestern North America. It is characterized by a continental climate and a growing season moisture deficit. Winters are cold and dry and summers are warm to hot. Natural vegetation is grasslands with few trees or shrubs. The dominant soils are Chernozemic with a relatively high soil organic matter and fertility levels. Soils range in age from young where they were glaciated to old where they occur south of the extent of the last glaciers. Growing season drought limits choice of crops or limits land use to grazing or to irrigated agriculture. Wheat is the most dominant crop under dryland conditions.

Warm Temperate Zone

This zone covers 21% of world's land and includes 18% of arable land. It ranges from 20 to 35o N and 20 to 35o S. Temperature permits growth all year and the frost free period is more than 200 days. Winters are mild. The agriculture system is determined by amount and seasonal distribution of precipitation.



Humid Zone. Land in the humid zone is now mostly cultivated, but native vegetation was wooded grassland, high grassland, and subtropical humid forest. Precipitation is adequate for more than six months of production, usually a cool season crop and a warm season crop. Soils are neutral to acid, including Chernozemic soils, moist soils such as Ultisols, and clayey soils such as Vertisols. Soils are not usually production-limiting.

Semi-arid and arid zone. This zone includes the great deserts of Africa, Asia, Australia, US, the Middle East and S. America. Soils range from Chernozemic to poorly developed Brunisolic soils. The major crops are wheat and sorghum where rainfed production is possible and a wide range of crops under irrigation.
3.5.2 Crop Production Systems
Humid cool-temperate zone

Development in Europe (Schusky, 1989, p. 104; Spiertz et al. 1992, p. 359). Temperate agricultural systems evolved in Europe from hunting and gathering to settled systems over thousands of years. The first settled systems had small diversity of crops, such as wheat, oats, barley, rye, peas and lentils. Animal production was based on cattle for draft and pigs for food. The Romans introduced chickens, grapes and basic tools.

A system of large estates evolved, based on the aristocracy which owned the land. In these systems, there was generally a central town, surrounded by plowed fields, then pasture, and woodlands. Individuals had rights to plowed fields, and the remaining land was held in common.

Farmers paid dues to manor.

The original system was a crop-fallow system of production. By 1000 AD, population pressure resulted in the need to increase agricultural productivity, and the dominant system shifted to two crops-fallow. Production on the large manors used hired labour and managers in a capitalistic organization with capital, labour and management supplied by different sources.

As urban population grew, demand for food increased, resulting in a transition from subsistence to commercial agriculture, especially during the Industrial Revolution.


Current Crop Production Systems (Bowden, 1979, p. 62; Thorne and Thorne, 1979, p. 152; Spiertz et al., 1992, p. 360). The agricultural systems of Temperate regions are now commercial in all parts of the world.

United States. The original production systems were based on maize with legumes to provide soil nitrogen and livestock feed. Small grains were used as cover or cash crops. Livestock was produced for meat, dairy and farm power.

Now, crop production in this region of the United States is mainly maize, soybeans, and forage crops. There is also some concentrated production of dairy products and hogs in specialized operations characterized by few producers, and a large number of animals per operation.

A large portion of this zone is referred to as the Corn Belt. The most common system there is a rotation of maize and soybeans. The region produces half of world's maize and 65% of the world's soybeans. The major secondary crop is winter wheat. It is possible to produce two crops in three years, but two crops per year generally not possible.

High levels of chemical inputs are used in the corn and soybean production, including the use of specially bred high yielding crop cultivars that are disease and insect resistant.



In Europe crops produced include wheat, oats, barley, rye, sorghums, potatoes, sugar beets and millet. Livestock products account for larger part of gross farm revenue than in the U.S. For example, in Sweden 40% of land in this zone is in grass and 40% is in cereals. Yields per ha are among highest in world, and are accomplished with high levels of inputs. Farm size is smaller than in the U.S.

Asia. China=s agricultural systems in this region are high intensity, multiple cropping and intercropping systems. The major crops are rice and wheat with production done in less mechanized ways than in other similar areas of the world.

Russia=s humid temperate areas are more northerly than in US, so there is a larger climatic limitation. The main crops are wheat and maize in highly mechanized systems that are less productive than in the US or Europe. This is mainly due to more climate limitations and less input use.


Arid and semi-arid cool temperate zone

Soils are generally nonlimiting in arid cool regions, but climate limits production. In the arid zone, drought is a problem and agriculture may require irrigation. In the semi-arid zone, which is farther north, the is less of a moisture limitation, but the frost-free season is short. Cropping systems are intensive where crops are gown under irrigation, and extensive where they are gown under dryland conditions. Dryland production systems are characterized by low yields and large farms that require large equipment and large inputs of fertilizer and herbicides.

Only short season and drought tolerant crops, such as small grains (spring wheat, barley, oats), oil seeds (canola, flax, sunflowers, safflower, mustard) and forages (alfalfa, sainfoin, cool season grasses) can be successfully grown. These are usually specialized cultivars adapted to the dry or cold conditions of the region. Yields are determined by moisture conditions at critical stages of crop development. Lack of soil moisture or high atmospheric demand (hot dry winds) at heading stages can reduce yield. Water use efficiency increases with latitude because there are lower temperatures and more moisture in the north portions of the cool temperate zones.

The most common rotations are crop-fallow to three crops-fallow in monoculture cropping systems. Water conservation is important where PET exceeds precipitation and crop growth depends on stored soil moisture. Specialized techniques have developed to store soil water the driest regions of this zone. These include snow trapping with standing stubble, plant barriers, snow ridges, and shelter belts; maintenance of high SOM and good soil surface structure to maximize the infiltration rate an, prevent runoff; and summer fallow. Summer fallow has benefits, although the efficiency of this system is questionable. It stabilizes yields (reduces risk of crop failure), allows for tillage weed control, and reduces labour at seeding and harvest, but it is also associated with salinity, soil erosion, leaching of N mineralized during the fallow period, and rapid decomposition of soil organic matter.

Erosion by wind and water is a common problem in cultivated areas of this zone. The rate of erosion is affected by slope steepness, soil texture, surface roughness and soil cover. Control can be achieved if farmers avoid cultivation of steep slopes, keep sandy textured soils under permanent cover, keep the soil surface covered with crop residue, avoid tillage fallow, and plant shelterbelts and grass strips within large fields.


Soils are relatively fertile, but because most of the crops harvested are exported, soils can become depleted of nutrients if adequate fertilizer is not used. Nitrogen is required in all areas, P and K may be required on sandy soils or where parent materials are low in those nutrient.

Farming systems are highly mechanized, so fossil fuel inputs are high, and weed control by a combination of tillage and herbicides is common. All of the temperate farming systems in North America are at the top of the technology ladder. They rely on specialized equipment for tillage, seeding, application of pesticides, harvesting, drying, storing and transporting of grain. Even though they are highly technological and employ economies of scale, net profit per farm may be low or negative. There reasons for poor profitability are related to high input costs relative to commodity prices. The high cost of fossil fuel increases all inputs costs, such as steel, synthetic rubber tires, diesel fuel, and coal generated electricity. High levels of productivity has not meant high income for farmers.


3.6 Agricultural systems produce and modify their own environments

Agricultural systems are products of their biophysical and socio-economic environments, but they also modify their environment through feedback and other control mechanisms. Thus, agriculture is both a product and a producer of environment. This idea is illustrated in the following example that compares farming in Brazil and Saskatchewan.


Shifting Cassava Production in N.E. Brazil versus Grain Farming in Saskatchewan

Physical Environment - What is different?

1. Climate - rainfall, temperature. Climate determines the natural vegetation.

2. Natural vegetation - Tropical savanna versus mixed-grass Prairie. The climate and natural vegetation under which a soil forms, affects the nature of the soil.

3. Soils - Tropical soils are Oxisols. They are highly weathered, acidic, with low organic matter, low fertility, and Al toxicity. Prairie soils are Chernozems. They are relatively young and unweathered, neutral to alkaline ph., with relatively high quantity and quality of organic matter, and high fertility.

Differences in climate, natural vegetation and soils affect the cropping system because crops are adapted to specific environments. Cassava requires a long season, high temperatures, and dry conditions. Spring wheat can mature within a short season, and temperate, semi-arid to subhumid climate.

Social Environment - What is different?

1. People. Levels of education, class distinction, and population density vary.

2. Community structure is affected by how the land is used. In shifting production, the people are semi-nomadic, they live in small groups (tribes), they are mostly self-sufficient with few inputs (fossil fuel, fertilizer, pesticides). The land is cleared, cropped and abandoned to naturally revegetate for 5 to 30 years. The grain farm has more technology (mechanization) and intensive energy use, it has a permanent location headquartered at a farmstead with about one family per farm. Land is in crop or fallow every year. Services and infrastructure provided by industry and government




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