Crop cultivation systems
Cropping systems vary among farms depending on the available resources and constraints; geography and climate of the farm; government policy; economic, social and political pressures; and the philosophy and culture of the farmer.Shifting cultivation (or slash and burn) is a system in which forests are burnt, releasing nutrients to support cultivation of annual and then perennial crops for a period of several years.[35] Then the plot is left fallow to regrow forest, and the farmer moves to a new plot, returning after many more years (10–20). This fallow period is shortened if population density grows, requiring the input of nutrients (fertilizer or manure) and some manual pest control. Annual cultivation is the next phase of intensity in which there is no fallow period. This requires even greater nutrient and pest control inputs.
Further industrialization led to the use of monocultures, when one cultivar is planted on a large acreage. Because of the low biodiversity, nutrient use is uniform and pests tend to build up, necessitating the greater use of pesticides and fertilizers.[34] Multiple cropping, in which several crops are grown sequentially in one year, and intercropping, when several crops are grown at the same time, are other kinds of annual cropping systems known as polycultures.[35]
In subtropical and arid environments, the timing and extent of agriculture may be limited by rainfall, either not allowing multiple annual crops in a year, or requiring irrigation. In all of these environments perennial crops are grown (coffee, chocolate) and systems are practiced such as agroforestry. In temperate environments, where ecosystems were predominantly grassland or prairie, highly productive annual cropping is the dominant farming system.[35]
Livestock production systems
Animals, including horses, mules, oxen, water buffalo, camels, llamas, alpacas, donkeys, and dogs, are often used to help cultivate fields, harvest crops, wrangle other animals, and transport farm products to buyers. Animal husbandry not only refers to the breeding and raising of animals for meat or to harvest animal products (like milk, eggs, or wool) on a continual basis, but also to the breeding and care of species for work and companionship.
Livestock production systems can be defined based on feed source, as grassland-based, mixed, and landless.[37] As of 2010,
30% of Earth's ice- and water-free area was used for producing
livestock, with the sector employing approximately 1.3 billion people.
Between the 1960s and the 2000s, there was a significant increase in
livestock production, both by numbers and by carcass weight, especially
among beef, pigs and chickens, the latter of which had production
increased by almost a factor of 10. Non-meat animals, such as milk cows
and egg-producing chickens, also showed significant production
increases. Global cattle, sheep and goat populations are expected to
continue to increase sharply through 2050.[38] Aquaculture
or fish farming, the production of fish for human consumption in
confined operations, is one of the fastest growing sectors of food
production, growing at an average of 9% a year between 1975 and 2007.[39]During the second half of the 20th century, producers using selective breeding focused on creating livestock breeds and crossbreeds that increased production, while mostly disregarding the need to preserve genetic diversity. This trend has led to a significant decrease in genetic diversity and resources among livestock breeds, leading to a corresponding decrease in disease resistance and local adaptations previously found among traditional breeds.[40]
Grassland based livestock production relies upon plant material such as shrubland, rangeland, and pastures for feeding ruminant animals. Outside nutrient inputs may be used, however manure is returned directly to the grassland as a major nutrient source. This system is particularly important in areas where crop production is not feasible because of climate or soil, representing 30–40 million pastoralists.[35] Mixed production systems use grassland, fodder crops and grain feed crops as feed for ruminant and monogastric (one stomach; mainly chickens and pigs) livestock. Manure is typically recycled in mixed systems as a fertilizer for crops.[37]
Landless systems rely upon feed from outside the farm, representing the de-linking of crop and livestock production found more prevalently in Organisation for Economic Co-operation and Development(OECD) member countries. Synthetic fertilizers are more heavily relied upon for crop production and manure utilization becomes a challenge as well as a source for pollution.[37] Industrialized countries use these operations to produce much of the global supplies of poultry and pork. Scientists estimate that 75% of the growth in livestock production between 2003 and 2030 will be in confined animal feeding operations, sometimes called factory farming. Much of this growth is happening in developing countries in Asia, with much smaller amounts of growth in Africa.[38] Some of the practices used in commercial livestock production, including the usage of growth hormones, are controversial.[41]
Production practices
Tillage
is the practice of plowing soil to prepare for planting or for nutrient
incorporation or for pest control. Tillage varies in intensity from
conventional to no-till.
It may improve productivity by warming the soil, incorporating
fertilizer and controlling weeds, but also renders soil more prone to
erosion, triggers the decomposition of organic matter releasing CO2, and reduces the abundance and diversity of soil organisms.[42][43]Pest control includes the management of weeds, insects, mites, and diseases. Chemical (pesticides), biological (biocontrol), mechanical (tillage), and cultural practices are used. Cultural practices include crop rotation, culling, cover crops, intercropping, composting, avoidance, and resistance. Integrated pest management attempts to use all of these methods to keep pest populations below the number which would cause economic loss, and recommends pesticides as a last resort.[44]
Nutrient management includes both the source of nutrient inputs for crop and livestock production, and the method of utilization of manure produced by livestock. Nutrient inputs can be chemical inorganic fertilizers, manure, green manure, compost and mined minerals.[45] Crop nutrient use may also be managed using cultural techniques such as crop rotation or a fallow period.[46][47] Manure is used either by holding livestock where the feed crop is growing, such as in managed intensive rotational grazing, or by spreading either dry or liquid formulations of manure on cropland or pastures.
Water management is needed where rainfall is insufficient or variable, which occurs to some degree in most regions of the world.[35] Some farmers use irrigation to supplement rainfall. In other areas such as the Great Plains in the U.S. and Canada, farmers use a fallow year to conserve soil moisture to use for growing a crop in the following year.[48] Agriculture represents 70% of freshwater use worldwide.[49]
According to a report by the International Food Policy Research Institute, agricultural technologies will have the greatest impact on food production if adopted in combination with each other; using a model that assessed how eleven technologies could impact agricultural productivity, food security and trade by 2050, the International Food Policy Research Institute found that the number of people at risk from hunger could be reduced by as much as 40% and food prices could be reduced by almost half.[50]
"Payment for ecosystem services (PES) can further incentivise efforts to green the agriculture sector. This is an approach that verifies values and rewards the benefits of ecosystem services provided by green agricultural practices."[51] "Innovative PES measures could include reforestation payments made by cities to upstream communities in rural areas of shared watersheds for improved quantities and quality of fresh water for municipal users. Ecoservice payments by farmers to upstream forest stewards for properly managing the flow of soil nutrients, and methods to monetise the carbon sequestration and emission reduction credit benefits of green agriculture practices in order to compensate farmers for their efforts to restore and build SOM and employ other practices." [51]
Crop alteration and biotechnology
Crop alteration has been practiced by humankind for thousands of years, since the beginning of civilization. Altering crops through breeding practices changes the genetic make-up of a plant to develop crops with more beneficial characteristics for humans, for example, larger fruits or seeds, drought-tolerance, or resistance to pests. Significant advances in plant breeding ensued after the work of geneticist Gregor Mendel. His work on dominant and recessive alleles, although initially largely ignored for almost 50 years, gave plant breeders a better understanding of genetics and breeding techniques. Crop breeding includes techniques such as plant selection with desirable traits, self-pollination and cross-pollination, and molecular techniques that genetically modify the organism.[52] Domestication of plants has, over the centuries increased yield, improved disease resistance and drought tolerance, eased harvest and improved the taste and nutritional value of crop plants. Careful selection and breeding have had enormous effects on the characteristics of crop plants. Plant selection and breeding in the 1920s and 1930s improved pasture (grasses and clover) in New Zealand. Extensive X-ray and ultraviolet induced mutagenesis efforts (i.e. primitive genetic engineering) during the 1950s produced the modern commercial varieties of grains such as wheat, corn (maize) and barley.[53][54]
The Green Revolution popularized the use of conventional hybridization
to sharply increase yield by creating "high-yielding varieties". For
example, average yields of corn (maize) in the USA have increased from
around 2.5 tons per hectare (t/ha) (40 bushels per acre) in 1900 to
about 9.4 t/ha (150 bushels per acre) in 2001. Similarly, worldwide
average wheat yields have increased from less than 1 t/ha in 1900 to
more than 2.5 t/ha in 1990. South American average wheat yields are
around 2 t/ha, African under 1 t/ha, and Egypt and Arabia up to 3.5 to 4
t/ha with irrigation. In contrast, the average wheat yield in countries
such as France is over 8 t/ha. Variations in yields are due mainly to
variation in climate, genetics, and the level of intensive farming
techniques (use of fertilizers, chemical pest control, growth control to avoid lodging).[55][56][57]Genetic engineering
Main article: Genetic engineering
See also: Genetically modified food, Genetically modified crops, Regulation of the release of genetic modified organisms and Genetically modified food controversies
Genetically modified organisms (GMO) are organisms whose genetic material has been altered by genetic engineering techniques generally known as recombinant DNA technology.
Genetic engineering has expanded the genes available to breeders to
utilize in creating desired germlines for new crops. Increased
durability, nutritional content, insect and virus resistance and
herbicide tolerance are a few of the attributes bred into crops through
genetic engineering.[58] For some, GMO crops cause food safety and food labeling
concerns. Numerous countries have placed restrictions on the
production, import or use of GMO foods and crops, which have been put in
place due to concerns over potential health issues, declining
agricultural diversity and contamination of non-GMO crops.[59] Currently a global treaty, the Biosafety Protocol,
regulates the trade of GMOs. There is ongoing discussion regarding the
labeling of foods made from GMOs, and while the EU currently requires
all GMO foods to be labeled, the US does not.[60]Herbicide-resistant seed has a gene implanted into its genome that allows the plants to tolerate exposure to herbicides, including glyphosates. These seeds allow the farmer to grow a crop that can be sprayed with herbicides to control weeds without harming the resistant crop. Herbicide-tolerant crops are used by farmers worldwide.[61] With the increasing use of herbicide-tolerant crops, comes an increase in the use of glyphosate-based herbicide sprays. In some areas glyphosate resistant weeds have developed, causing farmers to switch to other herbicides.[62][63] Some studies also link widespread glyphosate usage to iron deficiencies in some crops, which is both a crop production and a nutritional quality concern, with potential economic and health implications.[64]
Other GMO crops used by growers include insect-resistant crops, which have a gene from the soil bacterium Bacillus thuringiensis (Bt), which produces a toxin specific to insects. These crops protect plants from damage by insects.[65] Some believe that similar or better pest-resistance traits can be acquired through traditional breeding practices, and resistance to various pests can be gained through hybridization or cross-pollination with wild species. In some cases, wild species are the primary source of resistance traits; some tomato cultivars that have gained resistance to at least 19 diseases did so through crossing with wild populations of tomatoes.[
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