Land use in the tropics

• ﻿Tropical climate zone of the earth
• Tropical rainforest in Amazonia
Satellite image of the Amazon
Deforestation of the Amazon in 2009
Slash and burn in Zambia
Satellite image of slash and burn cells in Sumatra
rice
manioc
sweet potato
Yams
Brazil nut
Slash and burn lane
Corn
Pinus caribea planting
eucalyptus
Cuban home garden
Sugar cane
Kapok tree
Babassu palms
cocoa
Leucaena glauca
Centrosema

The land use in the tropics describes the diverse use of the land mass in the tropical climate zone by the people and its activities. Since the greatest population growth is observed in the tropical regions of the world, there are urgent measures to increase agricultural productivity - or, on the other hand, to protect and permanently secure the natural foundations of life through the following alternatives:

• strongly increased production growth on previously used agricultural land
• Agricultural colonization and development of unused areas
• more efficient use and distribution of fertile land and products
• Recultivation of degraded areas (salinization, erosion and hard grass savannahs due to incorrect pasture use or overuse )

On the other hand, the extreme conditions in the apparently rich and fertile tropics (abundant rainfall , year-round solar radiation and heat, abundant vegetation ) pose some problems for human use, for example because of the often poor soils (especially due to the heavy rain) .

Land use in the humid tropics

In the tropics, forest stands are dwindling due to intensified forest management (softwood plantations , use of precious wood such as mahogany or wood expansion), the production of pastureland and a strong increase in population and the planned and unplanned settlement of tropical forest areas. The largest increases are recorded in Africa. In South America the area of ​​the tropical rainforest decreased from 550 million hectares (1978) to 330 million hectares (2000). The traditional form of management on these sites is slash and burn farming . The Amazonia, for example, was developed like a mosaic along the slopes and was taken over by settlers from the poorer states of northeastern Brazil, who had to learn other forms of cultivation here. Areas that were "overused" within a very short time were bought up by speculators and turned into pastureland by sowing grass legumes. Radical mechanical clearing by bulldozers and the removal of the root stocks usually prevent the regrowth of successional vegetation. Most of the plants in the rainforest reproduce vegetatively, so that the fallow land is not overgrown by the forest again. For wood expansion, wide aisles are cut to transport the tree trunks to the nearest river, which quickly become erosion channels due to the heavy rainfall. Large-scale shifting cultivation is the main cause of the disappearance of the rainforests. Furthermore, the forests have to give way because of the construction of reservoirs or the surface mining of mineral resources combined with environmental pollution and wild settlements (see Serra Pelada ). The energy needs of the settlers and miners are mostly covered by the production of charcoal . The consequence of clearing with heavy machinery is increasing soil degradation and accelerated humus degradation, deterioration of the soil structure, severe erosion from surface water and the spread of undesirable pioneer plants such as hard grasses. The slash and burn areas are recorded by satellite.

The nutrient shortage of the tropical rainforest was described by Goodland as follows:

" The tropical rainforest is a desert, covered with trees "

- Goodland & Irvin

Tropical rainforest as an ecosystem

Tropical rainforest climates are found in the Caribbean , Central America , northern and central South America , West Africa , the Central African Congo Basin , Madagascar , West India , Indochina , Indonesia and northern Australia , between the northern and southern tropics, or 10 ° north and south of the equator . The tropical rainforest makes up a total of 17 million square kilometers and 3.4% of the world surface. The net primary production of total biomass is 15 billion tons of carbon per year and a productivity per unit area of ​​0.90 P / A. As an ecosystem, the tropical rainforest is characterized by a very high level of biodiversity and complexity . The high biomass production results in relatively closed nutrient cycles with a balanced temperature and humidity regime. There is a typical daytime climate with average temperatures of 28 ° C. Due to the “sponge effect” of the most diverse plant communities during the daily precipitation events, there is hardly any danger of erosion . A dry microclimate can only occur in the crown area of ​​the forest trees due to the intense tropical sunlight . While temperature fluctuations of 7 to 12 ° C are measured at a tree height of 18 meters, the deviation is only 1 to 3 ° C at a height of one meter. The water balance is very balanced due to the interaction of evapotranspiration and precipitation. 75% of the rainwater can be found in the plant ecosystem . Dry events only occur with extensive deforestation of rainforests. South American rainforest soil is relatively poor in nutrients due to its low cation exchange capacity. The plants take up a large part of the nutrients in their broad-based and near-surface root system and release them back to the soil via leaf shedding , where it is quickly converted again by highly active soil organisms ( e.g. mycorrhizal fungi). There is only a relatively small proportion of nutrients in the soil itself. African slash and burn construction releases a high proportion of nutrients via aerosols and dust particles, which are transported via Atlantic trade winds to the Amazonia, where they ensure nutrient input. The Asian rainforest has the greatest biodiversity with 700 species / ha, followed by Central Amazonia with 500 species / ha. In last place are the African rainforests with only 250-300 species / ha.

Tropical soils

As a rough subdivision, a distinction is made between zonal and intrazonal soils; in the former, climate and vegetation were decisive for soil development and the latter are characterized by pedogenic factors. Azonal soils are young and mostly very fertile soils that are very suitable for high-yield arable farming. The dominant soils of Amazonia are already heavily weathered Oxisole (also known as "Latisole") Ultisole and Alfisole . The age of a soil is mostly negatively correlated with its nutrient content. Oxisols are characterized by a high iron and aluminum content and a good soil structure with stable micro-aggregates, but often show a clay depletion of the topsoil. The aluminum toxicity quickly becomes a limiting factor for a sensitive crop like maize .

Cultivation problems in the humid tropics

• high soil acidity: aluminum, manganese and iron toxicity and phosphate fixation
• low base saturation in the soil
• low cation exchange capacity (CEC) and high nutrient leaching
• absolute phosphorus deficiency
• Nitrogen deficiency
• low nutrient reserves in the soil
• compacted subsoil layers, iron concretions
• Soil compaction after cultivation
• low water holding capacity
• high to very high precipitation intensity (tropical heavy rain)
• temporary excess and lack of water
• Water erosion on slopes and loss of topsoil
• high humidity and thus high infection pressure from fungal diseases
• no climate-related growth pause
• strong sunlight and the resulting increased floor temperature to over 35 ° C and the death of important microorganisms
• strong population increase and settlement of marginal soils

Structure and types of management forms

• Shifting (shifting cultivation)
• Forestry arboriculture
• Agricultural tree and shrub cultures such as coffee, cocoa, rubber, oil palms
• Agroforestry as joint agricultural ( plant production and partially also pasture management ) and forestry use
• semi-permanent cultivation, for example grazed fallow bush
• Ley farming with pasture and annual crops
• Irrigated agriculture (rice)
• Pasture management with grass / legume pastures and low livestock / area
• annual cultures mostly monocultures or mixed cultures (multiple cropping)

In the 1970s, shifting cultivation was still one of the most common forms of tropical land use in Africa and Asia at 45%. 17% was accounted for by permanent arable farming and 4% by plantation farming Shifting cultivation is mostly practiced by non-sedentary ethnic groups, although in view of the strong increase in world population and the declining availability of land, this extensive form of farming can hardly be pursued. After a certain forest area has been cleared, the remaining tree stumps are burned and the area can be used for agriculture for one to a maximum of five years. Due to the strongly declining nutrient content and deteriorated soil structure, most crops then have to be given up, since further use is no longer possible due to severe soil degradation due to erosion and heavy weeds and grass growth. Fallow forest takes around 10 to 20 years to fully regenerate . While there is still enough space available in Amazonia for resource-saving shifting cultivation, the forests in Central America are exhausted (as of 1991). As an alternative, numerous agroforestry systems have emerged in Mexico and Costa Rica .

The measured variable is the so-called land use factor

${\ displaystyle {\ frac {number of cultivation years} {number of fallow fields +/- cultivation years}} * 100}$

• semi-permanent cultivation> 30 R <70
• permanent attachment> 70 R <100

Loss of yield from continuous use of agricultural crops in the humid tropics

• 70% cassava after the 3rd year ( Congo )
• 50% corn after the 3rd year (eastern Honduras )
• 40% cotton after the 5th year (southern Sudan )
• 10% peanut after the 2nd year (Congo)

Certain indicator plants (wild plants) show the nutrient deficiency earlier.

In traditional slash-and-burn agriculture, maize comes first because of its highest nutritional requirements, and lastly the less demanding cassava.

forestry

85% of the logging is done for the production of firewood for local needs, only 16% for the production of industrial wood for national consumption or export . The main suppliers are Malaysia and Indonesia and the main importing countries are Japan , USA , China and many EU countries . A large part of the sawn and veneer logs comes from the tropics (as of 1991).

However, it must be taken into account that approx. 80% of the logging in the always humid tropics is illegal and therefore cannot be precisely determined. Only about 20% of the tropical timber is legally felled, with only a small part of it paying attention to sustainable forestry (e.g. by using light machines, smaller clearances, taking into account the direction in which the trees fall, etc.).

Use of resources in the rainforest

• Complete mechanical clearing leads to a desertification of the area in the long term
• Shifting farming with improved productivity
• Sustainable agriculture is only possible on suitable areas
• semi-permanent cultivation as a transition phase for permanent cultivation, is usually only practiced for cash crops for export
• ecologically adapted permanent cultivation, for example agroforestry

Agroforestry

In agroforestry systems there is a double use of the rainforest with an emphasis on agriculture and pasture management. Cuba and Costa Rica are countries where agroforestry systems have traditionally been practiced. House gardens (span. Conuco) with mango trees , citrus ssp., Papaya, plantains (span. Plátanos), coffee and pineapples are part of the typical appearance of the Cuban country. These systems have been further developed since 1975, as a lack of land caused by high population pressure, increased livestock and large-scale deforestation led to severe soil degradation and erosion, especially on slopes.

Agroforestry is seen as the most ecologically adapted form of land use for the humid tropics because:

• permanent ground cover is guaranteed
• little tillage is necessary
• optimal nutrient supply through plant communities
• maximum perspiration is guaranteed
• the humus level is maintained.

These land use systems and the interactions between their plant communities are being researched at the ICRAF (International Center for Research in Agroforestry) in Nairobi , Kenya and partly also at the CATIE (Centro Agronómico Tropical de Investigación y Enseñanza) in Turrialba, Costa Rica . Originally, agroforestry or forest cultivation was also practiced in Central Europe before industrial agriculture, today still in Spain and some other Mediterranean countries. In most developing countries, food production has the highest priority (see Green Revolution ), so that permanent crops are increasingly prevailing. Agroforestry with a high degree of diversification remains an alternative for locations that cannot be mechanized, for example due to slopes. Agroforestry is the internationalization of an old system that has been tried and tested for sensitive ecosystems. The aim of an agroforestry system is the food supply through locally adapted cultivation of fruits, nuts, mushrooms, oils, game and pet meat, secondly energy supply through firewood and thirdly fodder production for livestock farming. The beekeeping can serve as an additional source of income. The focus is on yield security, not maximum yields. The forest has the effect of a "sponge" to hold on to the valuable nutrients during heavy tropical rain. Agroforestry as a low-input system has self-sustaining material and energy cycles and additional mineral fertilizers can usually be dispensed with. Pest invasions can almost be ruled out in an agroforestry system due to the numerous interactions. Because of allelopathy , inhibitory effects can also occur within the plant communities.

65% of Tanzanian coffee is produced in agroforestry systems, known zones are around Kilimanjaro and Mont Meru . These are highly complex management systems for small areas with coffee, citrus and papaya as predominantly useful plants, on which productive and sustainable agriculture is practiced. However, this system is severely threatened by insufficient food production, strong population growth and increased migration to the Tanzanian forest areas. The traditional coffee cultivation in Mexico is also practiced in a mixed culture with shade trees (Inga edulis), plantains, citrus and beans. Similar systems with hill cultivation of yams and maize can also be found in Nigeria, although it is noticeable that crops that require a lot of care, such as yams, are grown in the immediate vicinity of the huts. Based on the tree communities of the tropical rainforest, floor cultivation is sometimes also practiced. The arrangement of the plant communities appears to be random, although there is a system behind it based on centuries of agricultural experience. "Alley cropping" is practiced in many places in Southeast Asia. Rice and maize or coconut palms with cassava are cultivated between the rows of trees in the teak plantations , whereby both fruits are pushed back due to the increasing shade in the course of the vegetation period. Javanese house gardens often consist of coconut palms combined with fruit trees ( guava ) and lower shrubs such as papaya and manioc. From the GTZ numerous projects for Ecofarming were in Rwanda accompanied the large population increase and increased erosion problems on the hills by the increased productivity could not be collected. Local low input systems based on plantain, Albizia umbrella acacia, Grevillea silice together with intercropping from corn, beans, sweet potatoes, soy and cocoyam (Colocasia esculenta or Xanthosoma spp.) Were examined. In Central America and Colombia , coffee is found in the company of plantains and beans and other legumes , especially at high altitudes . In the Mediterranean area olive trees together with wheat.

An important measured variable is the LER or Land Equivalent Ratio M: mixed culture; R: pure culture; I: intercrop; j:? ${\ displaystyle {\ frac {Yi * M} {Yi * R}} * {Yj * M} {Yj * R}}$

The LER expresses the relation of pure culture to mixed culture and is represented in the following index function: LER = Xm / Xr + Ym / Yr X / Y - culture; m, r - mixed culture, pure culture

All mixed cultures (MCS: multiple cropping systems) have in common the economic flexibility, since there is no overproduction problem as with pure cultures . Disadvantages are the high manual workload in complex systems, yields in the low to medium range and no immediate short-term result. Agroforestry is based on the principles of long-term, sustainable and viable agriculture . In Southeast Asia there are completely self-sufficient systems: pigs are housed in the immediate vicinity of a pond and their dung feeds water hyacinths and is also composted or used as mulch . The water hyacinths form the basis of life for the microorganisms that tilapia cichlids feed on.

Case study agroforesting in the coffee gardens of Costa Rica

Problem

The main task of agriculture is to feed the exponentially growing world population . Agricultural productivity is increased on the one hand by intensifying and increasing the input of production factors of the existing land use and on the other hand by opening up hitherto not yet cultivated landscape areas. Since small farmers are hardly able to take on large amounts of outside capital , they have to produce their food themselves with the means available. The formation of reserves is hardly possible with the low subsistence yields. In Costa Rica there has long been a tendency to reclaim forested areas and convert primary forest ( tropical rainforest ) into agricultural land, which is associated with irreversible erosion and loss of soil fertility on slopes. Due to the strong humus shrinkage and fertile topsoil, productivity on marginal areas drops within a few years. Exploitation corridors for logging make the forests accessible for shifting cultivation with serious consequences for the ecosystem, since reforestation usually does not take place. Traditional Native American land use systems outside of the gathering economy were geared towards producing food and forest products in a small concentrated area in order to sell the surplus production in local markets. For a long time, Costa Rica was characterized by monostructured agriculture with a one-sided export orientation of coffee, bananas, sugar cane and beef.

Study area

The canton (span. Cantón) Acosta-Puriscal in the volcanic low mountain range of Costa Rica, 40 kilometers southwest of the capital San José , which since about the middle of the 19th century was examined. is intensely populated. This area was settled relatively late, as rough environmental conditions and a dense forest that was difficult to penetrate made urbanization difficult. Small-scale subsistence farming with maize and beans , market fruits (cash crops) such as coffee and extensive pasture farming dominate in this area . Year-round accessibility and infrastructure are provided, and numerous state rural development measures have been carried out here.

climate

The climate of Costa Rica is divided into thermal altitude levels:

Thermal altitudes of Costa Rica and their agricultural use
designation Vegetation form height Average temperature Crops
Tierra Caliente tropical lowland rainforest up to 400 m 24 to 31 ° C Cocoa, sugar cane, bananas, rice, corn
Tierra Templada tropical mountain rainforest, cloud and cloud forest up to 1700 m 18 to 24 ° C Coffee, tobacco, corn, citrus fruits
Climate diagram of San José / Costa Rica
Acosta-Puriscal Canton Costa Rica
Citrus fruit
Pejibaye

In the Acosta-Puriscal region there is a tropical humid climate with a defined dry period in Acosta between December and January and Puriscal between February and March. The average temperatures are around 20 ° C. The seasonal rainy season takes place in Acosta from June to October and in Puriscal with precipitation maximums from March to December. Otherwise the precipitation is distributed relatively evenly over the year.

Geology and soils

In the canton of Acosta-Puriscal there are heights between 200 and 1600 m, a low mountain range with relatively large differences in altitude and a slope of 20 to 75%. The soils are relatively clayey soils with a high humus content and proportion of organic material. They are moderately to strongly acidic and have a high cation exchange capacity (KAK). Of the nutrients, potassium can become a deficiency factor in some locations.

vegetation

The natural vegetation consists of tropical lowland rainforest with transitions to the premontane wet forest. In 1985 only about 8.5% were forested, mostly in hard-to-reach source regions.

Land use development

As a result of the increase in population, the agricultural area was increasingly extended to deforested border soils with a steep relief. In addition, pasture farming increased, which greatly promoted erosion and the decline in soil fertility . Many workers migrated to the urban conurbation of San José due to the low income opportunities. When coffee revenues fell in the past, the investment and expense costs for mineral fertilizers and biocides increased . The aim of the agricultural development measures was to sustainably increase agricultural income through efficient and export-oriented coffee production.

Settlement history

Before the conquest by the Spanish conquistadores, the Indios operated slash and burn. In the years 1561 to 1573, simple forms of agriculture were established. Between 1779 and 1790, subsistence agriculture was replaced in many places by cocoa, sugar cane and cotton. Coffee was first planted in 1821. Favorable climate and extremely fertile soil of volcanic origin were a real coffee - Boom arise. In the same year Costa Rica became independent and coffee became the country's main export product. Thus, an oligarchy of large landowning coffee-growing families established itself in the Meseta Central (high plateau of San José) and land prices rose dramatically. During this time, OFICAFE (Oficina de Café) was founded to regulate quality and pricing. In 1931 a government decree was issued which allowed every farmer to take legal possession of this land after 5 years of cultivating coffee on fallow land or reclaimed land. In 1960 the first production cooperatives (span. Beneficiarios) emerged. In addition, pasture farming was promoted to export-oriented beef production , thus increasing mechanical clearing of rainforests and extensive agricultural colonization . In the 1980s, the then still fertile soils were largely eroded and hardly had any bearing capacity for annual crops.

Operational structures

The mean farm sizes in this region are between 7 and 14 hectares. Agriculture focuses on the cultivation of annual crops such as corn and beans and as a source of income coffee, tobacco, citrus fruits and other types of fruit. With the cattle breeds Cebú, Brahman Cebú and Criollo, extensive pasture management is practiced, the number of cattle rose to 3 million in the 1980s and the area of ​​pastures increased to 68% of the country's area.

Factors inhibiting production
• Loss of soil due to erosion
• Nutrient deprivation through permanent cultivation and grazing without nutrient return
• obsolete coffee stocks
• insufficient regulation and distribution of shade trees on coffee plantations
• improper plant protection
• Low productivity grazing
• Labor shortage due to rural exodus
• insufficient marketing and transport of agricultural products
• high prices of production factors (fertilizers and pesticides)
• hardly any possibility of borrowing

Espinoza's research showed that agroforestry by smallholders was the most ecologically stable and sustainable option for this area. Shade trees such as coral trees (Erythrina poeppingiana), laurel ( Cordia alliodora ), Andean alder ( Alnus acuminata ) and West Indian cedar ( Cedrela odorata ) combined with breadnut trees ( Brosimum alicastrum ), white-headed mimosa ( Leucaena leucocephala ) deliver stable yields. Fiber agaves ( Yucca ssp.) And Pejibaye palms ( Bactris gasipaes ) serve as wind protection or delimitation of the areas. Rainbow eucalyptus ( Eucalyptus deglupta ) can also be used for firewood .

Systems of permanent use in the tropics

Permanent crops are:

• Trees (rubber, citrus ssp., Mango, kapok etc.)
• Palms (oil palm, coconut palm, babassu palm, pejibaye ( Bactris gasipaes ) etc.)
• Shrubs ( cocoa , coffee, tea etc.)

Coffee cultures

Coffee is grown in pure culture without shade (for example Brazil ) or in pure culture with shade (for example Colombia ); Mixed cultures with small-scale subsistence agriculture can be found in Costa Rica , for example . The first two systems strive for maximum yields with fast, high profits, in the third system the focus is on yield security and the low input of mineral fertilizers and pesticides. Typical shade trees are Grevillea, Robusta, Inga, legume trees (for example Caesalpinieae), Erythrinia etc., so the soil temperature is kept relatively constant. The canopy of leaves reduces the effect of the wind and prevents “splash erosion” from the impact of raindrops during heavy tropical rain events. The infection pressure of dangerous fungal diseases, for example from coffee rust , is drastically reduced.

Annual crops

Typical forms of cultivation include wet rice cultivation on terraces, which is traditionally at home in Asia, as a permanent system of use without damage to crop rotation . Some fields have been cultivated for over 100 years. Sugar cane has a similar self-tolerance and can also be used permanently (for example the annual permanent crops in the Valle del Cauca / Colombia). With these plants, productivity can be increased by using high-yield varieties (HYV), resistant varieties or varieties that are tolerant of abiotic stress factors or an insufficient supply of water and nutrients. Furthermore, yields are increased by using varieties with improved mineral fertilizer or urea utilization and legumes or N-fixing blue-green algae ( Azolla anabaena ) as green manure or for biological nitrogen enrichment. When growing several crops per year, varieties with a short vegetation period are used, ratoon cropping can also be useful or the use of the remaining water from rice cultivation for other crops. Green manuring or mulching, for example with the kudzu bean (Pueraria lobata), has strong positive effects on soil biology and important soil-dwelling organisms such as rhizobia, mycorrhizal fungi and earthworms. False phases maintain soil productivity in the long term, as they maintain nutrient enrichment, biological nitrogen fixation, increase the humus content, important physical properties of the soil and reduce the spread of pests, plant diseases and weeds. Due to the growing population and the high demand for food in developing countries, efforts are being made to keep the fallow phases as short as possible. The IITA (International Institute of Tropical Agriculture) in Ibadan / Nigeria deals with scientific questions of sustainable agriculture and tropical land use systems, including alley cropping. Two-year field experiments showed, for example, that a mixed culture of maize and leucaena ( white-headed mimosa Leucaena leucocephala ) with moderate nitrogen fertilization provided the highest yields. In contrast to mixed cultures with N-fixing legumes, mineral nitrogen fertilization has an immediate effect.

Nitrogen and phosphorus are some of the most important limiting factors for crop growth of crops in the tropics. Phosphate is hardly available to plants in heavily weathered tropical soils, so that a circular economy and the "recycling" of nutrients are of great importance. One-sided N fertilization on the coffee plantations of Costa Rica has led to significant yield reductions.

Forage plants

Water buffalo in India
Panicum maximum
Setaria sphacelata

Extensive tropical grazing is v. a. practiced in Brazil. In the humid tropics, intensive pasture management with suitable cattle breeds ( e.g. zebu ) is only suitable on very humid soils, on which no arable farming can be carried out.

Requirements for this are:

• gentle soil preparation
• Grass sowing to suppress endemic legumes and multiple dose nitrogen fertilization
• Regulated grazing so as not to endanger the natural composition of species

In the case of improper pasture management, sterile pasture steppes can form due to devastation. Even apparently green and lush pastures can contain plants with very little nutritional value and the grazing animals starve.

Typical forage grasses and forage legumes are:

• Guinea gras ( Panicum maximum )
• Golden timothy ( Setaria sphacelata )
• Star gras ( Cynodon dactylon )
• Zebra grass ( Hyparrhenia rufa )
• Savanna grass ( Axonopus compressus )
• Centro ( Centrosema molle ; syn.Centrosema pubescens )
• Glycine wightii

Most of the forage legumes used today come from Central and South America. The CIAT in Cali / Colombia has, among other things, the research assignment for the genetic improvement of tropical willow plants.

Land use in tropical high altitude regions

Cloud forest
Mountain slope in the cloud forest
Altiplano
Amaranthus plant
Oca tubers

In the Cordilleras from Colombia to Peru , sedentary arable crops with a wide range of cultivation options formed as a result of a sharp increase in population. The lower infection pressure from plant diseases was one of the reasons for moving out of the warmer valley regions. In the high altitude zones, the temperature becomes a limiting factor for plant growth and the topography of the hillside areas promotes erosion. The vegetation consists of humid rainforest in the coastal region, which changes into montane rainforest, followed by cloud forest and cloud forest . The highland zone itself belongs to the arid climatic area in the absence of trade and Pacific precipitation . In Ecuador there is a fully mechanized agriculture mostly in large estates and intensively managed banana plantations in the coastal lowlands with year-round rainfall. From an altitude of 800/1000 meters, coffee plantings and mixed cultures in subsistence agriculture take their place. From 1500 meters, maximum yields are no longer to be expected and the use of mineral fertilizers is less due to the marginal forms of cultivation that prevail there.

Wheat and barley brought by the Spanish conquerors displaced the endemic crops of the Incas . Barley has established itself in many places because this grain can be grown up to 3500 meters above sea level, has low nutritional requirements and is cold-tolerant.

Cultivation problems at tropical altitudes

• anthropogenic soil erosion: through logging in the primary forest, fire and pasture use (soil damage from hoof kicks ) the top soil layers are lost and washed away
• Deforestation and landslides in the event of a lasting disruption of the water balance
• Separation of forest and pasture: grazing is extended to unsustainable altitudes
• Pasture use and the one-sided browsing can lead to heavy weed growth in mountain pasture, which in the worst case turns into wasteland
• Cold air ingress: in areas with little vegetation, sudden frosts can damage the crops in certain stages of development
• Declining soil fertility and fewer soil organisms correlate with altitude (exception: volcanic soils of the cloud forests on Java )

Management forms at tropical altitudes

For some time now, research has been carried out on the endemic, locally well-adapted Inca plants such as quinoa (Chenopodium quinoa), tarwi / Andean lupine (Lupinus mutabilis) or oca (Oxalis tuberosa). The soil for the plants described was tilled by the Incas with simple hoes to prevent erosion. Mechanical processing with the reversible plow usually leads to severe erosion and loss of topsoil. As a result of erosion, the nutrients accumulate in the mountain valleys, which are more used for agriculture. Quinoa or Inca wheat is adapted for extreme altitude locations between 3000 and 4000 meters and is used in a variety of ways, including as a protein plant. In these locations, only crops with quinoa and small Altiplano potatoes are possible. Other plants are Amaranto (Amaranthus caudatus), which is grown similar to cereals and used as grain or vegetables, Olluco (Ullucus tuberosus) similar to potatoes, Añu or Isaña (Tropaeolum tuberosum) with yields of 20 to 30 tons per hectare and Maca (Lepidium meyenii), which occurs up to an altitude of 4000 meters and is processed into a starchy paste. The CIP (Centro Internacional de la Papa) in Lima has the research assignment to research the genetic potential of potatoes and other starchy Andean tubers and to develop sustainable cultivation methods.

In arid areas, sorghum is also grown in mountainous areas at an altitude of 800 to 900 meters; in Colombia, for example, 180,000 MT were produced in 2009. Between 1000 and 1500 meters (in Colombia the so-called Zona Cafetalera), there are medium mixed cultures with average farm sizes of 2 to 5 hectares of coffee and plantains , which are mostly integrated into the natural vegetation. The plantains serve as a source of shade for the young coffee plants and are gradually removed the stronger the coffee bushes develop. From 3000 meters on there is mostly only bush vegetation.

Primarily, the settlement took place at springs in the highlands with partly terrace cultivation of beans and maize, later also barley. In order to control the excess water, plowing was carried out or stone walls were built. Cattle manure as an organic fertilizer replaces expensive mineral fertilizers. Tubers such as oca and potatoes are often freeze-dried in the field. Mixed cultures are intended to reduce the risk of an overall failure. In the vicinity of large cities, production is more intensive with a higher input for maximum yields (maize 7–10 t / ha) in order to supply the growing urban population. Foil covering as frost protection is impractical in developing countries because of the high costs. In barren dry steppes, barley is sown at wide intervals, here only yields of up to 0.6 t / ha can be achieved. Quinoa is now also grown as a fully automated threshing crop on large fields, which further promotes erosion. The hygroscopic calcium oxalate prevents excessive perspiration in quinoa and helps the plant to survive dry phases. Quinoa is often added to white bread flour as an extension. The Andean indigenous population still feeds very heavily on quinoa.

Land use in the semi-arid tropics (SAT)

Millet grains
Sorghum
peanut
Typical African acacia

Climate zones with 2 to 5 months of precipitation and an annual rainfall of 100 to 1000 mm are called semi-arid areas. In the semi-arid tropics, optimal water use is at the fore of agriculture. Depending on the intensity, rain-fed agriculture or artificial irrigation is carried out. Irrigation can allow up to 3 harvests per year. In 1993, 250 million hectares worldwide were under irrigation , often not used in a resource-saving manner due to overwatering. Every year up to 1.6 million hectares are irreversibly lost due to irrigation errors and salinization. This was increasingly the case in India and Pakistan due to the intensification of agricultural production .

In the Sahel region of West Africa, with annual rainfall of less than 500 mm, various resource-saving cultivation methods have emerged. Staple foods such as sorghum , corn and peanuts are often, for example, shade trees as shea grown / Sheabutterbaum (Vitellaria paradoxa or Butyrospermum parkii). The trees serve as firewood and provide high-fat seeds. Other plant communities with Néré (Parkia biglobosa), tamarind (Tamarindus india) and Ethiopian palmyra palms (Borassus aethiopum). The trees also fulfill an important function as protection against wind erosion.

Acacias predominate where only marginal dry field cultivation can be carried out.

Salinisation of soils

• Soils in the area of ​​influence of salt lakes
• Soils with capillary rise from saline groundwater
• Soils with salinisation from slope or surface water

Artificial, anthropogenic salinization is caused by serious errors in irrigation management. There is thus the risk of alkalization, which is expressed by the SAR value (Sodium Adsorption Ratio). Where irrigation is used, suitable drainage must be provided to avoid salinisation of the topsoil. The term desertification has been used since 1977, which describes the decline in production in a dry area due to human interference such as incorrect land use, overgrazing, soil erosion, etc.

Rain farming

In rain-fed agriculture, the limiting factor of water must be safeguarded by a number of measures. A permanent covering of the topsoil with green manure plants or mulch increases the infiltration rate of the rain and keeps the precipitation in the soil longer. Another measure is the preservation of the humus layer through organic fertilization. Soil cultivation must be carried out as gently as possible in order to keep the evapotranspiration of soil and plants as low as possible. The main crop should be sown at the beginning of the rainy season.

literature

• Willem Cornelis Beets: Raising and Sustaining Productivity of Smallholder Farming Systems in the Tropics. A Handbook of Sustainable Agricultural Development. AgBé, Alkmaar 1990, ISBN 974-85676-1-3 (English).
• M. Bonell, LA Bruijnzeel: Forests, Water and People in the Humid Tropics. 2 volumes: Past, Present and Future Hydrological Research for Integrated Land and Water Management. Cambridge University Press, 2009 (English).
• Dean Current, Ernst Lutz and Sara Scherr: Costs, Benefits and Farmer Adoption of Agroforestry, Project Experience in Central America and the Caribbean, a CATIE-IFPRI World Bank Project. In: World Bank Environment Paper. No. 14, Washington 1995 (English).
• Werner Doppler: Agricultural operating systems in the tropics and subtropics. Ulmer, Stuttgart 1991, ISBN 3-8001-4084-5 .
• LP Espinoza: Studies on the importance of the tree component in agroforestry coffee cultivation using examples from Costa Rica. In: Göttingen contributions to agriculture and forestry in the tropics and subtropics. Issue 10, Göttingen 1985.
• FP Huibers: Rainfed Agriculture in a Semi-Arid Tropical Climate. Aspects of Land- and Water Management for Red Soils in India. CABI Abstracts, Wageningen 1985 (English).
• Godfrey Lubulwa, Benson Wafula, et al. a .: Dry Land Farming in the Semi-Arid Tropics of Kenya. ACIAR project experience. ACIAR Working Papers, Canberra 1996, ISBN 1-86320-163-7 (English).
• Sigmund Rehm: Handbook of Agriculture and Food in the Developing Countries. Volume 3: Basics of plant production in the tropics and subtropics. Göttingen 1989, ISBN 3-8001-3065-3 .
• Sigmund Rehm, Gustav Espig: The cultivated plants of the tropics and subtropics. Ulmer, Göttingen 1984, ISBN 3-8001-4108-6 .
• Wolfgang Ritter: Land use in the humid tropics. Status report on research activities in the Federal Republic of Germany 1985–1990. Working group for tropical and subtropical agricultural research, Bonn 1990.
• Volkmar Vareschi: Vegetation ecology of the tropics. Ulmer, Stuttgart 1980, ISBN 3-8001-3423-3 .
• SP Wani, OP Rupela, KK Lee: Sustainable Agriculture in the Semi-Arid Tropics Through Biological Nitrogen Fixation in Grain Legumes. In: Plant and Soil. Volume 174, No. 1–2, Springer Netherlands, 2004, pp. 29–49 (English; PDF download possible ).

Individual evidence

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