Environmental impact of agriculture

Climate change and agriculture are interrelated processes, both of which take place on a worldwide scale. Global warming is projected to have significant impacts on conditions affecting agriculture, including temperature, precipitation and glacial run-off. These conditions determine the carrying capacity of the biosphere to produce enough food for the human population and domesticated animals. Rising carbon dioxide levels would also have effects, both detrimental and beneficial, on crop yields. Assessment of the effects of global climate changes on agriculture might help to properly anticipate and adapt farming to maximize agricultural production. Although the net impact of climate change on agricultural production is uncertain it is likely that it will shift the suitable growing zones for individual crops. Adjustment to this geographical shift will involve considerable economic costs and social impacts.

At the same time, agriculture has been shown to produce significant effects on climate change, primarily through the production and release of greenhouse gases such as carbon dioxide, methane, and nitrous oxide. In addition, agriculture that practices tillage, fertilization, and pesticide application also releases ammonia, nitrate, phosphorus, and many other pesticides that affect air, water, and soil quality, as well as biodiversity.[1] Agriculture also alters the Earth's land cover, which can change its ability to absorb or reflect heat and light, thus contributing to radiative forcing. Land use change such as deforestation and desertification, together with use of fossil fuels, are the major anthropogenic sources of carbon dioxide; agriculture itself is the major contributor to increasing methane and nitrous oxide concentrations in earth's atmosphere.[2]

Most of the methane emissions result from the use of livestock, in particular ruminants such as cattle and pigs. Other livestock as poultry, fish, ... has a far lower impact.[3] Some solutions are being developed to counter the emissions of ruminants. Strategies include using biogas from manure,[4] genetic selection,[5][6] immunization, rumen defaunation, outcompetition of methanogenic archaea with acetogens,[7] introduction of methanotrophic bacteria into the rumen,[8][9] diet modification and grazing management, among others.[10][11][12] Certain diet changes (such as with Asparagopsis taxiformis) allow for a reduction of up to 99% in ruminant greenhouse gas emissions.[13][14] Due to these negative impacts, but also for reasons of farming efficiency (see Food vs. feed), one projection mentions a large decline of livestock at least some animals (i.e. cattle) in certain countries by 2030.[15][16]

Deforestation is clearing the Earth's forests on a large scale worldwide and resulting in many land damages. One of the causes of deforestation is to clear land for pasture or crops. According to British environmentalist Norman Myers, 5% of deforestation is due to cattle ranching, 19% due to over-heavy logging, 22% due to the growing sector of palm oil plantations, and 54% due to slash-and-burn farming.[17]

Deforestation causes the loss of habitat for millions of species, and is also a driver of climate change. Trees act as a carbon sink: that is, they absorb carbon dioxide, an unwanted greenhouse gas, out of the atmosphere. Removing trees releases carbon dioxide into the atmosphere and leaves behind fewer trees to absorb the increasing amount of carbon dioxide in the air. In this way, deforestation exacerbates climate change. When trees are removed from forests, the soils tend to dry out because there is no longer shade, and there are not enough trees to assist in the water cycle by returning water vapor back to the environment. With no trees, landscapes that were once forests can potentially become barren deserts. The removal of trees also causes extreme fluctuations in temperature.[18]

In 2000 the United Nations Food and Agriculture Organization (FAO) found that "the role of population dynamics in a local setting may vary from decisive to negligible," and that deforestation can result from "a combination of population pressure and stagnating economic, social and technological conditions."[19]

Irrigation can lead to a number of problems:[20]

Among some of these problems is the depletion of underground aquifers through overdrafting. Soil can be over-irrigated because of poor distribution uniformity or management wastes water, chemicals, and may lead to water pollution. Over-irrigation can cause deep drainage from rising water tables that can lead to problems of irrigation salinity requiring watertable control by some form of subsurface land drainage. However, if the soil is under irrigated, it gives poor soil salinity control which leads to increased soil salinity with consequent buildup of toxic salts on soil surface in areas with high evaporation. This requires either leaching to remove these salts and a method of drainage to carry the salts away. Irrigation with saline or high-sodium water may damage soil structure owing to the formation of alkaline soil.

Synthetic pesticides such as 'Malathion', 'Rogor', 'Kelthane' and 'confidor' are the most widespread method of controlling pests in agriculture. Pesticides can leach through the soil and enter the groundwater, as well as linger in food products and result in death in humans and non-targeted wildlife.[21] A wide range of agricultural chemicals are used and some become pollutants through use, misuse, or ignorance. The erosion of topsoil, which can contain chemicals such as herbicides and pesticides, can be carried away from farms to other places.[22] Pesticides can be found in streams and groundwater. Atrazine is a herbicide used to control weeds that grow among crops.[23] This herbicide can disrupt endocrine production which can cause reproductive problems in mammals, amphibians and fish that have been exposed.[23] Pollutants from agriculture have a huge effect on water quality. Agricultural nonpoint source (NPS) solution impacts lakes, rivers, wetlands, estuaries, and groundwater. Agricultural NPS can be caused by poorly managed animal feeding operations, overgrazing, plowing, fertilizer, and improper, excessive, or badly timed use of Pesticides. Pollutants from farming include sediments, nutrients, pathogens, pesticides, metals, and salts.[24] Animal agriculture can also cause pollutants to enter the environment. Bacteria and pathogens in manure can make their way into streams and groundwater if grazing, storing manure in lagoons and applying manure to fields is not properly managed.[23]

Listed below are additional and specific problems that may arise with the release of pollutants from agriculture.

• Pesticide drift
  • soil contamination
  • air pollution spray drift
• Pesticides, especially those based on organochloride
• Pesticide residue in foods
• Pesticide toxicity to bees
  • List of crop plants pollinated by bees
  • Pollination management
• Bioremediation
• Dead zones caused by fertilizers runoff

Soil degradation is the decline in soil quality that can be a result of many factors, especially from agriculture. Soils hold the majority of the world's biodiversity, and healthy soils are essential for food production and adequate water supply.[25] Common attributes of soil degradation can be salting, waterlogging, compaction, pesticide contamination, a decline in soil structure quality, loss of fertility, changes in soil acidity, alkalinity, salinity, and erosion. Soil erosion is the wearing away of topsoil by water, wind, or farming activities.[22] Topsoil is very fertile, which makes it valuable to farmers growing crops.[22] Soil degradation also has a huge impact on biological degradation, which affects the microbial community of the soil and can alter nutrient cycling, pest and disease control, and chemical transformation properties of the soil.[26]

• soil contamination
  • sedimentation

Plasticulture is the use of plastic mulch in agriculture. Farmers use plastic sheets as mulch to cover 50-70% of the soil and allow them to use drip irrigation systems to have better control over soil nutrients and moisture. Rain is not required in this system, and farms that use plasticulture are built to encourage the fastest runoff of rain. The use of pesticides with plasticulture allows pesticides to be transported easier in the surface runoff towards wetlands or tidal creeks. The runoff from pesticides and chemicals in the plastic can cause serious deformations and death in shellfish as the runoff carries the chemicals towards the oceans.[27]

In addition to the increased runoff that results from plasticulture, there is also the problem of the increased amount of waste from the plastic mulch itself. The use of plastic mulch for vegetables, strawberries, and other row and orchard crops exceeds 110 million pounds annually in the United States. Most plastic ends up in the landfill, although there are other disposal options such as disking mulches into the soil, on-site burying, on-site storage, reuse, recycling, and incineration. The incineration and recycling options are complicated by the variety of the types of plastics that are used and by the geographic dispersal of the plastics. Plastics also contain stabilizers and dyes as well as heavy metals, which limits the number of products that can be recycled. Research is continually being conducted on creating biodegradable or photodegradable mulches. While there has been a minor success with this, there is also the problem of how long the plastic takes to degrade, as many biodegradable products take a long time to break down.[28]

The environmental impact of agriculture can vary depending on the region as well as the type of agriculture production method that is being used. Listed below are some specific environmental issues in various different regions around the world.

• Hedgerow removal in the United Kingdom.
• Soil salinisation, especially in Australia.
• Phosphate mining in Nauru
• Methane emissions from livestock in New Zealand. See Climate change in New Zealand.
• Environmentalists attribute the hypoxic zone in the Gulf of Mexico as being encouraged by nitrogen fertilization of the algae bloom.
• Coupled systems from agricultural trade leading to regional effects from cascading effects and spillover systems. Environmental factor (Socioeconomic Drivers Section)

Conservation tillage is an alternative tillage method for farming which is more sustainable for the soil and surrounding ecosystem.[32] This is done by allowing the residue of the previous harvest's crops to remain in the soil before tilling for the next crop. Conservation tillage has shown to improve many things such as soil moisture retention, and reduce erosion. Some disadvantages are the fact that more expensive equipment is needed for this process, more pesticides will need to be used, and the positive effects take a long time to be visible.[32] The barriers of instantiating a conservation tillage policy are that farmers are reluctant to change their methods, and would protest a more expensive, and time-consuming method of tillage than the conventional one they are used to.[33]

Other specific methods include: permaculture; and biodynamic agriculture which incorporates a spiritual element.

• Category: Sustainable agriculture
• Biological pest control