Rotational grazing
In agriculture, rotational grazing, as opposed to continuous grazing, describes many systems of pasturing, whereby livestock are moved to portions of the pasture, called paddocks, while the other portions rest. Each paddock must provide all the needs of the livestock, such as food, water and sometimes shade and shelter. The approach often produces lower outputs than more intensive animal farming operations, but requires lower inputs, and therefore sometimes produces higher net farm income per animal. Approach. In rotational grazing livestock are moved to portions of the pasture, called paddocks, while the other portions rest. The intent is to  allow the pasture plants and soil time to recover. Healing native rangeland may require a combination of burning and rotational grazing. Rotational grazing can be used with ruminants such as beef or dairy cattle, sheep or goats, or even pigs. The herds graze one portion of pasture, or a paddock, while allowing the others to recover. The length of time a paddock is grazed will depend on the size of the herd and the size of the paddock and local environmental factors. Resting grazed lands allows the vegetation to regrow. Rotational grazing is especially effective because grazers do better on  the more tender younger plant stems. These systems may or may not leave parasites behind to die off, minimizing or eliminating the need for de-wormers, depending if the rotational time is smaller or larger than the parasitic life cycle. Benefits. Herd health benefits arise from animals having access to both space and fresh air. Freedom of movement within a paddock results in increased physical fitness, which limits the potential for injuries and abrasion, and sometimes depending on the system reduces the potential of exposure to high levels of harmful disease-causing microorganisms and insects. In a concentrated animal feeding  operation it is normal for a large number of animals to continuously occupy a small area. By comparison, with managed grazing, the animals are able to live in a more natural environment. The animals experience less disease and fewer foot ailments, depending on the rotational system being used. Rotational grazing has been said to be more environmentally friendly in certain cases. Many pastures undergoing certain types of rotational grazing are less susceptible to soil erosion. Paddocks might require fewer inputs. These grazing regimes are sometimes said to be more resilient and more capable of responding to changing environmental conditions. Rotational  grazing may reduce greenhouse gas emissions such as carbon dioxide, nitrous oxides, and methane. Adaptive multi-paddock grazing can result in a net carbon sink. Problems. A key element of this style of animal husbandry is that either each grazed area must contain all elements needed for the animals (water source, for instance) or the feed or water source must be moved each time the animals are moved. Having fixed feeding or watering stations can defeat the rotational aspect, leading to degradation of the ground around the water supply or feed supply if additional feed is provided to the animals . Special care must be taken to ensure that high use areas do not become areas where mud, parasites or diseases are spread or communicated. Several problems are related to shade in pasture areas. Although shade provides relief from heat and reduces the risk of heat stress, animals tend to congregate in these areas which leads to nutrient loading, uneven grazing, and potential soil erosion. Ruminal tympany, also known as bloat, is a common serious problem when grazing ruminants on fresh, young pasture, and if left untreated can be fatal. This problem occurs when foam producing compounds in plants are digested  by cows, causing foam to form in the rumen of the animal and not allowing animals to properly belch gas. Animals are especially susceptible to bloat if they are moved to new pasture sources when they are particularly hungry and especially on young, fresh and wet legumes. It is therefore important to ensure that the herd is eating enough at the end of a rotation when forage will be more scarce, limiting the potential for animals to gorge themselves when turned out onto new paddocks. The risk of bloat can be mitigated by careful management of rotations, seeding the non -bloating European legume species "Lotus corniculatus" in pasturelands, reducing the amount of legumes/increasing grasses, providing sufficient supplemental feeding and extra fodder when turning out on new paddocks, reducing the size of the paddock when livestock is first turned out, and daily rations of the anti-foaming agent poloxalene mixed well into the fodder. Weed control. A well managed rotational grazing system has low pasture weed establishment because the majority of niches are already filled with established forage species, making it harder for weeds to compete and become established. The use of multiple species in the pasture helps to minimize  weeds. Established forage plants in rotational grazing pasture systems are healthy and unstressed due to the "rest" period, enhancing the competitive advantage of the forage. Additionally, in comparison to grain crop production, many plants which would be considered weeds are not problematic in perennial pasture. However, certain species such as thistles and various other weeds, are indigestible or poisonous to grazers. These plant species will not be grazed by the herd and can be recognized for their prevalence in pasture systems. A key step in managing weeds in any pasture system is identification. Once the undesired species in a pasture  system are identified, an integrated approach of management can be implemented to control weed populations. It is important to recognize that no single approach to weed management will result in weed free pastures; therefore, various cultural, mechanical, and chemical control methods can be combined in an weed management plan. Cultural controls include: avoiding spreading manure contaminated with weed seeds, cleaning equipment after working in weed infested areas, and managing weed problems in fencerows and other areas near pastures. Mechanical controls such as repeated mowing, clipping, and hand weeding can also be used to effectively manage weed infestations by weakening the  plant. These methods should be implemented when weed flower buds are closed or just starting to open to prevent seed production. Although these first two methods reduce need for herbicides, weed problems may still persist in managed grazing systems and the use of herbicides may become necessary. Use of herbicides may restrict the use of a pasture for some length of time, depending on the type and amount of the chemical used. Frequently, weeds in pasture systems are patchy and therefore spot treatment of herbicides may be used as a least cost method of chemical control. Nutrient availability and soil  fertility. If pasture systems are seeded with more than 40% legumes, commercial nitrogen fertilization is unnecessary for adequate plant growth. Legumes are able to fix atmospheric nitrogen, thus providing nitrogen for themselves and surrounding plants. Although grazers remove nutrient sources from the pasture system when they feed on forage sources, the majority of the nutrients consumed by the herd are returned to the pasture system through manure. At a relatively high stocking rate, or high ratio of animals per hectare, manure will be evenly distributed across the pasture system. The nutrient content in these manure sources should be adequate to  meet plant requirements, making commercial fertilization unnecessary. Rotational grazing systems are often associated with increased soil fertility which arises because manure is a rich source of organic matter that increases the health of soil. In addition, these pasture system are less susceptible to erosion because the land base has continuous ground cover throughout the year. High levels of fertilizers entering waterways are a pertinent environmental concern associated with agricultural systems. However, rotational grazing systems effectively reduce the amount of nutrients that move off-farm which have the potential to cause environmental degradation. These systems are fertilized with on-farm sources , and are less prone to leaching as compared to commercial fertilizers. Additionally, the system is less prone to excess nutrient fertilization, so the majority of nutrients put into the system by manure sources are utilized for plant growth. Permanent pasture systems also have deeper, better established forage root systems which are more efficient at taking up nutrients from within the soil profile. Economics. Although milk yields are often lower in rotational systems, net farm income per cow is often greater as compared to confinement operations. This is due to the additional costs associated with herd health and purchased feeds are  greatly reduced in management intensive rotational grazing systems. Additionally, a transition to rotational grazing is associated with low start-up and maintenance costs. Another consideration is that while production per cow is less, the number of cows per acre on the pasture can increase. The net effect is more productivity per acre at less cost. The main costs associated with transitioning rotational grazing are purchasing fencing, fencers, and water supply materials. If a pasture was continuously grazed in the past, likely capital has already been invested in fencing and a fencer system. Cost savings to graziers can also be recognized  when one considers that many of the costs associated with livestock operations are transmitted to the grazers. For example, the grazers actively harvest their own sources of food for the portion of the year where grazing is possible. This translates into lower costs for feed production and harvesting, which are fuel intensive endeavors. Rotational grazing systems rely on the grazers to produce fertilizer sources via their excretion. There is also no need for collection, storage, transportation, and application of manure, which are also all fuel intensive. Additionally, external fertilizer use contributes to other costs such as labor, purchasing costs. Rotational  grazing results in time savings because the majority of work which might otherwise require human labor is transmitted to the herd. Criticism. Managers have found that rotational grazing systems can work for diverse management purposes, but scientific experiments have demonstrated that some rotational grazing systems do not always necessarily work for specific ecological purposes. This controversy stems from two main categorical differences in rotational grazing, prescribed management and adaptive management. The performance of rangeland grazing strategies are similarly constrained by several ecological variables establishing that differences among them are dependent on the effectiveness of those management models. Depending on the  management model, plant production has been shown to be equal or greater in continuous compared to rotational grazing in 87% of the experiments.