How we grow food has enormous consequences for ecosystems and the climate. Sustainable agriculture aims to meet present needs without compromising future capacity, while regenerative agriculture goes further by actively restoring soil health and biodiversity. Conventional farming often relies on monoculture, the practice of growing a single crop over large areas, which simplifies ecosystems, increases pest pressure, and depletes soils. Better practices include crop rotation, which alternates crops to maintain soil fertility and disrupt pest cycles; no-till farming, which avoids disturbing soil to reduce erosion and emissions; cover cropping, which grows plants between main crops to protect and enrich soil; and agroforestry, which integrates trees with crops or livestock to create more diverse, resilient systems. Organic farming differs from conventional farming mainly by restricting synthetic inputs like pesticides and fertilizers, although both can vary widely in their ecological footprint.
Soil itself is a critical and often overlooked resource. Topsoil is the uppermost, most fertile layer, and it can take centuries to form. Soil erosion, the removal of soil by wind or water, is accelerated by poor agricultural practices, and soil degradation describes the broader decline in soil quality and productivity. Salinization, the buildup of salts in soil, often results from improper irrigation and renders land unable to support crops. Excess fertilizers and sewage washing off fields cause eutrophication, the over-enrichment of waterways with nutrients that trigger algal blooms. As algae die and decompose, oxygen is consumed, creating ocean dead zones, low-oxygen areas where most marine life cannot survive. The largest dead zones often appear at the mouths of major agricultural rivers.
Pollution extends beyond nutrients into the air and the oceans. The Great Pacific Garbage Patch is a swirling concentration of marine plastic debris in the North Pacific, and microplastics, plastic fragments smaller than 5 mm, are now found throughout the environment and food chains. Toxic substances pose additional risks through bioaccumulation, the buildup of substances in an organism over time, and biomagnification, the increase in concentration as one moves up the food chain. Mercury, for example, concentrates in top predators such as tuna and swordfish. Air pollution takes many forms: acid rain forms when sulfur dioxide and nitrogen oxides from burning fossil fuels combine with water in the atmosphere; the ozone layer, a stratospheric shield of O₃ that absorbs harmful ultraviolet radiation, was damaged by chlorofluorocarbons (CFCs) until the 1987 Montreal Protocol phased them out; photochemical smog forms when sunlight reacts with vehicle emissions; and particulate matter, especially fine particles designated PM2.5 and PM10, is a major health threat regulated under World Health Organization air quality guidelines.