As the leading sector in terms of water consumption, agriculture has a significant impact on global fresh water supply. Irrigation alone consumes 70 percent of the world’s supply of fresh water, while only 8 percent is used for domestic purposes. This has a significant environmental impact and has resulted in water shortages throughout the world.
Of the world's total land area, 10.6 percent is arable land that is suitable for growing crops. With roughly 7 billion people on Earth, it is essential to maximise the amount of food that can be produced on this relatively small area. This has led to the widespread use of fertilisers and pesticides over the past half-century. Fertilisers in the runoff from farmland enter rivers, lakes and oceans, resulting in the process of eutrophication, in which the nitrogen from the fertilisers acts as a food source for algae. When the algae die, they consume the oxygen in the water, killing aquatic life. While pesticides are effective in protecting plants from disease, they also harm animals species and contaminate nearby waterways. Many types of pesticides contain carcinogens and chemicals that cause neurological diseases in humans.
Various agricultural practices have an impact on the environment:
Irrigation and water abstraction — These activities lead to soil salinisation and alkalisation; damage river ecosystems; and lower the water table. Irrigation may also increase emissions of the greenhouse gases nitrogen oxide and methane from soil.
Intensive cropping — Soil erosion caused by intensive agriculture increases the amount of sediment in runoff, contributing to water pollution. Intensive crop production also results in nutrient depletion, damaging the soil structure and reducing its fertility and adsorption capacity while increasing erosion and runoff.
Fertiliser use — The spreading of animal manure and artificial fertilisers results in the volatilisation of ammonia and emissions of nitrous oxide; the contamination of groundwater from leachate; the pollution of the drinking-water supply; and eutrophication and oxygen depletion in surface water bodies as a result of runoff, which encourages algae growth and kills fish populations. Fertilisers and manure also lead to soil acidification, and the heavy metals and phosphates that accumulate in the soil enter the food chain. The use of sewage sludge as a fertiliser leads to the accumulation of heavy metals and organic micro-pollutants that enter the food chain; and directly contaminates fauna and flora with microbial agents and chemicals.
Pesticide application — The use of pesticides results in the leaching of residues into groundwater, which can affect drinking water quality. Many pesticides contain persistent organic pollutants, which are organic compounds that are resistant to degradation. Their accumulation in food chains has a significant impact on human health and the environment. Pesticides can alter or destroy non-target organisms and damage wildlife, habitats and foods sources. The evaporation or volatilisation of pesticides results in them being carried by the wind and affecting ecosystems far from the point of application.
Intensive animal husbandry — Livestock farming results in emissions of methane and ammonia and the release of organic matter and nutrients into water bodies.
Canalisation — The construction of artificial waterways, or the conversion of rivers, leads to hydrological changes with negative impacts.
Drainage — Draining agricultural land lowers the water table and poses a threat to wetlands and the composition of grasslands, fens and similar habitats. It also causes the oxidation and acidification of organic soils, reducing their organic content and changing the soil structure.
The use of mechanical equipment — Tilling and ploughing cause increased amounts of dust and particulate matter in the air. This can lead to greater volumes of surface runoff, resulting in sedimentation, contamination and eutrophication in water bodies. The use of heavy machinery leads to soil compaction, increased surface runoff and greater sediment loads, while ploughing on slopes leads to the erosion of soil by water and wind.
Changes in land use — The removal of vegetation cover leads to soil erosion and increases surface runoff and sediment load, resulting in sedimentation, contamination and eutrophication in water bodies. The loss of hedgerows, woodlands, small watercourses and ponds results in a loss of landscape variety and a reduction in species diversity.
The following agricultural practices result in less damage to the environment: