Inagriculture,grazing is a method ofanimal husbandry whereby domesticlivestock are allowed outdoors tofree range (roam around) and consume wildvegetations in order toconvert the otherwise indigestible (byhuman gut)cellulose withingrass and otherforages intomeat,milk,wool and otheranimal products. Grazing is often done on lands that are unsuitable forarable farming, although there are occasions wherearable lands and even priorfarmlands are intentionally kept or converted topastures to raise commercially valuable grazing animals.
Farmers may employ many different strategies of grazing foroptimum production: grazing may be continuous, seasonal, orrotational within a grazing period. Longer rotations are found inley farming, alternating arable and fodder crops; in rest rotation, deferred rotation, and mob grazing, giving grasses a longer time to recover or leaving land fallow. Patch-burn sets up a rotation of fresh grass after burning with two years of rest.Conservation grazing proposes to use grazing animals to improve the biodiversity of a site.[1]
Grazing livestock on open grasslands, i.e.pastoralism, has existed as ahuman practice since thebeginning of agriculture;sheep andgoats weredomesticated bynomads before the first permanent settlements were constructed around 7000 BC, enablingcattle andpigs to be kept, and people who supervise grazing livestock are calledshepherds. In the vastEurasian steppe, migrating and grazing herds of sheep andhorse between different pasture regions had been the primary means offood production for theInner Asiahorseback nomads, with manynomadic empires rose and fell throughout history until theearly modern period. During thelate Medieval andearly modern England, manycommon lands used bypeasants forcrop farming wereenclosed and converted to pastures controlled bygentries to favorwool trades. Inmodern era,ranching is the more common method of raising grazing livestock, although artificially madefeeds such ashay andfodders are sometimes used to supplement grazing.
Livestock grazing contributes to many negative effects on the environment, includingdeforestation,extinction of native wildlife, pollution of streams and rivers,overgrazing,soil degradation,ecological disturbance,desertification,[2] andecosystem stability.[3][4]
Sheep, goats, cattle, and pigs were domesticated early in thehistory of agriculture. Sheep were domesticated first, soon followed by goats; both species were suitable fornomadic peoples. Cattle and pigs were domesticated somewhat later, around 7000 BC, once people started to live in fixed settlements.[5]
In America, livestock were grazed onpublic land from theCivil War. TheTaylor Grazing Act of 1934 was enacted after theGreat Depression to regulate the use of public land for grazing purposes.[6]
According to a report by theFood and Agriculture Organization, about 60% of the world's grassland (just less than half of the world's usable surface) is covered by grazing systems. It states that "Grazing systems supply about 9 percent of the world's production ofbeef and about 30 percent of the world's production ofsheep andgoat meat. For an estimated 100 million people inarid areas, and probably a similar number in other zones, grazing livestock is the only possible source of livelihood."[7]
Grazing management has two overall goals:
A proper land use and grazing management technique balances
It does this by allowing sufficient recovery periods for regrowth. Producers can keep a low density on a pasture, so as not to overgraze.[citation needed] Controlled burning of the land can help in the regrowth of plants.[10] Although grazing can be problematic for the ecosystem, well-managed grazing techniques can reverse damage and improve the land.[citation needed]
Oncommons in England and Wales, rights ofpasture (grassland grazing) andpannage (forest grazing) for each commoner are tightly defined by number and type of animal, and by the time of year when certain rights can be exercised. For example, the occupier of a particular cottage might be allowed to graze fifteen cattle, fourhorses,ponies ordonkeys, and fiftygeese, while the numbers allowed for their neighbours would probably be different. On some commons (such as theNew Forest and adjoining commons), the rights are not limited by numbers, and instead a 'marking fee' is paid each year for each animal 'turned out'.[11] However, if excessive use was made of the common, for example, in overgrazing, a common would be 'stinted'; that is, a limit would be put on the number of animals each commoner was allowed to graze. These regulations were responsive to demographic and economic pressure. Thus, rather than let a common become degraded, access was restricted even further.[12]
Ranchers andrange science researchers have developed grazing systems to improve sustainable forage production for livestock. These can be contrasted withintensive animal farming on feedlots.
With continuous grazing, livestock is allowed access to the same grazing area throughout the year.[13]
Seasonal grazing incorporates "grazing animals on a particular area for only part of the year". This allows the land that is not being grazed to rest and allow for new forage to grow.[14]
Rotational grazing "involves dividing the range into several pastures and then grazing each in sequence throughout the grazing period". Utilizing rotational grazing can improve livestock distribution while incorporating rest period for new forage.[14]
In ley farming, pastures are not permanently planted, but alternated betweenfodder crops and arable crops.[15]
Rest rotation grazing "divides the range into at least four pastures. One pasture remains rested throughout the year and grazing is rotated amongst the residual pastures." This grazing system can be especially beneficial when using sensitive grass that requires time for rest and regrowth.[14]
Deferred rotation "involves at least two pastures with one not grazed until after seed-set". By using deferred rotation, grasses can achieve maximum growth during the period when no grazing occurs.[14]
Patch-burn grazing burns a third of a pasture each year, no matter the size of the pasture. This burned patch attracts grazers (cattle orbison) that graze the area heavily because of the fresh grasses that grow as a result. The other patches receive little to no grazing. During the next two years the next two patches are burned consecutively, then the cycle begins anew. In this way, patches receive two years of rest and recovery from the heavy grazing. This technique results in a diversity of habitats that different prairie plants and birds can utilize—mimicking the effects of the pre-historical relationship between bison and fire, whereby bison heavily graze one area and other areas have opportunity to rest, based on the concept ofpyric herbivory.[10][16] TheTallgrass Prairie Preserve in northeastern Oklahoma has been patch-burn grazed with bison herds for over ten years. These efforts have effectively restored the bison–fire relationship on a large landscape scale of 30,000 acres (12,000 ha).[17] In the grazedheathland ofDevon, the periodic burning is known as swailing.[18]
Riparian area grazing is intended to improve wildlife[clarification needed] and their habitats. It uses fencing to keep livestock off ranges near streams or water areas until after wildlife or waterfowl periods, or to limit the amount of grazing to a short period of time.[14]
Conservation grazing is the use of grazing animals to help improve the biodiversity of a site. Due to their hardy nature,rare and native breeds are often used in conservation grazing.[19] In some cases, to re-establish traditionalhay meadows, cattle such as theEnglish Longhorn andHighland are used to provide grazing.[20]
A form of rotational grazing using as many small paddocks as fencing allows.[21]
Mob grazing is a system, said to be more sustainable, invented in 2002; it uses very large herds on land leftfallow longer than usual.[22]
Manyecological effects, which may be positive or negative, derive from grazing. Negative effects of grazing may includeovergrazing, increasedsoil erosion,compaction and degradation,deforestation,biodiversity loss,[7] and adversewater qualityimpacts from run-off.[23][24] Sometimes grazers can have beneficial environmental effects such as improving the soil with nutrient redistribution and aerating the soil by trampling, and by controlling fire and increasing biodiversity by removing biomass, controlling shrub growth and dispersing seeds.[7] In some habitats, appropriate levels of grazing may be effective in restoring or maintaining native grass and herb diversity inrangeland that has been disturbed by overgrazing, lack of grazing (such as by the removal of wild grazing animals), or by other human disturbance.[25][26]Conservation grazing is the use of grazers to manage such habitats, often to replicate the ecological effects of the wild relatives of domesticlivestock, or those of other species now absent or extinct.[27]
Grazer urine and faeces "recycle nitrogen, phosphorus, potassium and other plant nutrients and return them to the soil".[28] Grazing can reduce the accumulation of litter (organic matter) in some seasons and areas,[29] but can also increase it, which may help to combatsoil erosion.[30] This acts as nutrition for insects and organisms found within the soil. These organisms "aid incarbon sequestration and water filtration".[28]
When grass is grazed, dead grass and litter are reduced, which is advantageous for birds such aswaterfowl. Grazing can increasebiodiversity. Without grazing, many of the same grasses grow, for examplebrome andbluegrass, consequently producing amonoculture.[29] The ecosystems of North Americantallgrass prairies are controlled to a large extent by nitrogen availability, which is itself controlled by interactions between fires and grazing by large herbivores. Fires in spring enhance the growth of certain grasses. Herbivores preferentially graze these grasses, producing a system of checks and balances, and allowing higher plant biodiversity.[31] InEuropeheathland is acultural landscape which requires grazing by cattle,sheep or other grazers to be maintained.[32]
An author of theFood and Agriculture Organization (FAO) reportLivestock's Long Shadow,[33] stated in an interview:[34]
Grazing occupies 26 percent of Earth's terrestrial surface ... feed crop production requires about a third of all arable land ... Expansion of grazing land for livestock is also a leading cause of deforestation, especially in Latin America ... In the Amazon basin alone, about 70 percent of previously forested land is used as pasture, while feed crops cover a large part of the remainder.
Much grazing land has resulted from a process of clearance or drainage of other habitats such aswoodland orwetland.[35]
According to the opinion of theCenter for Biological Diversity,extensive grazing of livestock in the arid lands of the southwestern United States has many negative impacts on the local biodiversity there.[36]
Cattle destroy native vegetation, damage soils and stream banks, and contaminate waterways with fecal waste. After decades of livestock grazing, once-lush streams and riparian forests have been reduced to flat, dry wastelands; once-richtopsoil has been turned to dust, causing soil erosion, stream sedimentation and wholesale elimination of some aquatic habitats
In arid climates such as the southwestern United States, livestock grazing has severely degradedriparian areas, the wetland environment adjacent to rivers or streams. TheEnvironmental Protection Agency states that agriculture has a greater impact on stream and river contamination than any othernonpoint source. Improper grazing of riparian areas can contribute tononpoint source pollution of riparian areas.[37] Riparian zones in arid and semiarid environments have been calledbiodiversity hotspots.[38] The water, higherbiomass, favorablemicroclimate and periodic flood events together produce higher biological diversity than in the surrounding uplands.[39] In 1990, "according to theArizona state park department, over 90% of the original riparian zones of Arizona andNew Mexico are gone". A 1988 report of theGovernment Accountability Office estimated that 90% of the 5,300 miles of riparian habitat managed by theBureau of Land Management inColorado was in an unsatisfactory condition, as was 80% ofIdaho's riparian zones, concluding that "poorly managed livestock grazing is the major cause of degraded riparian habitat on federal rangelands".[40]
A 2013 FAO report estimated livestock were responsible for 14.5% ofanthropogenic greenhouse gas emissions.[41][42] Grazing is common inNew Zealand; in 2004,methane andnitrous oxide from agriculture made up somewhat less than half of New Zealand's greenhouse gas emissions, of which most is attributable tolivestock.[43] A 2008United States Environmental Protection Agency report on emissions found agriculture was responsible for 6% of total United States greenhouse gas emissions in 2006. This includedrice production,enteric fermentation in domestic livestock, livestockmanure management, and agriculturalsoil management, but omitted some things that might be attributable to agriculture.[44] Studies comparing themethane emissions from grazing and feedlot cattle concluded that grass-fed cattle produce much more methane than grain-fed cattle.[45][46][47] One study in theJournal of Animal Science found four times as much, and stated: "these measurements clearly document higher CH4 production for cattle receiving low-quality, high-fiber diets than for cattle fed high-grain diets".[45]
Agrivoltaics for grazing allows for shade for the animals and thevegetation so the soil retains a highermoisture level.[48] This approach not only reduces maintenance costs by minimizing the need for mechanical mowing but also enhances land productivity by integrating renewable energy production with agricultural use.[49] In the United States, more than 100,000 sheep graze at solar arrays, primarily in the South.[50][51] Organizations such as theAmerican Solar Grazing Association (ASGA) promotes best practices for co-locating solar energy and grazing operations.
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