The organic movement began as a reaction against synthetic
fertilizers, but it soon evolved into a big-tent alternative to many
aspects of modern agriculture, including chemical pesticides, preemptive
antibiotics, monocultures, factory farms and genetically engineered
crops. Below are some of the main environmental and human health arenas
in which supporters say organic farms beat conventional ones:

• Fertilizers: Depleted soil is a major cause of crop
failures, a problem that ancient farmers often solved with organic
fertilizers like animal dung, which can restore soil over time by
releasing nitrogen, phosphorus and potassium, as well as various
micronutrients. Other organic tactics for boosting soil quality include cover crops (aka “green manure”), crop rotation and composting.
But those all involve a lot of manual labor, and by the mid-1800s
chemists began finding shortcuts, like a way to make “superphosphate”
from sulfuric acid and phosphate rocks, or to make ammonia from trace
gases in the air and turn it into nitrogen fertilizers. Despite their
short-term benefits, though, these synthetic fertilizers have also been
linked to several long-term drawbacks. They’re costly to make, for one,
since the production of ammonia now accounts for roughly 2 percent of global energy use, and mining for phosphorus
is depleting the planet’s finite reserves. Overfertilization can also
harm crops — as well as human babies if nitrogen seeps into their
drinking water — and often triggers algae blooms and “dead zones.”

• Pesticides: Plenty of pest-killing chemicals are
available, but organic farms focus more on prevention than treatment.
Cover crops can suppress weeds before they sprout, while crop rotation
keeps plants one step ahead of diseases. Organic farmers may also grow
multiple crops in one place, known as “polyculture,” to capitalize on
pest-repelling species. Some “trap crops” even lure and kill bugs —
Japanese beetles are drawn to geraniums, for example, and a toxin in the
petals paralyzes the beetles
for 24 hours, usually enough time for something to kill them. But a
growing demand for food drove a global shift to synthetic pesticides
last century, especially once DDT and similar insecticides hit the
market. Several were later banned in the U.S., though, for a problem
that plagues many pesticides: persistence.
The longer a chemical sits outside without breaking down, the more
likely it is to accumulate, drift around and even move up the food
chain. Safe levels of human exposure vary widely, but on top of things
like brain damage and birth defects, some have also been linked to cancer. According to one review
of cancer studies from 1992 to 2003, “Most studies on non-Hodgkin
lymphoma and leukemia showed positive associations with pesticide
exposure,” and the reviewers add that “a few were able to identify
specific pesticides.” People living near farms may be directly exposed
to pesticides, although anyone else can be, too, just by eating a stick
of celery. It tops the USDA’s list of pesticide residues on food, followed by peaches, kale, strawberries and blueberries (see the interactive graphic above for more, or check out a list of the “Dirty Dozen” most pesticide-laced produce.)

• Crop diversity: Growing individual, isolated crops in
bulk has become common for large-scale farms, but since it’s an
unnatural way for most plants to grow, many require extra help. Known as
a monoculture, a vast field of one species is risky because all the
crops are vulnerable to the same diseases and conditions, setting up
disasters like the 1840s Irish Potato Famine.
Farms that use polyculture, however, not only enlist crops to protect
each other from pests, but can also still rely on the surviving crops if
one is killed by disease. And since they have those safeguards built
into their farming system, they have less need for fertilizers and
pesticides. They also have less need to plant genetically modified
organisms, a more recent breakthrough that has amplified the fight over
modern farming. GMOs are often bred to be tolerant of specific pests or
pesticides, but organic advocates say this creates an unnecessary
dependence on pesticides. The agribusiness giant Monsanto, for example,
sells Roundup herbicide as well as “Roundup-ready” crops genetically
engineered to tolerate Roundup. Critics also warn of “genetic drift”
from GMO pollen to wild species, and scientists in North Dakota even
recently found two herbicide-resistant varieties of GM canola plants
that had escaped from farms into the wild. But GMOs can sometimes help their natural neighbors, too — another recent study found that a certain kind of GM corn both protects itself from corn borer moths as well as non-GM corn planted nearby.

• Livestock: People have raised animals to eat for
millennia, starting with sheep and goats that nomadic tribes herded some
11,000 years ago. Cattle and pigs came next as nomads settled down on
farms, and modern chickens followed a few thousand years later; turkeys
took much longer to tame, finally giving in to the Aztecs around the
1300s. Farm animals were long raised outdoors in relatively low
concentrations, but that changed dramatically in the 20th century.
Chickens were raised in CAFOs,
aka “factory farms,” as early as the 1920s, and the rise of growth
hormones, vaccines and antibiotics paved the way for cattle and pork
CAFOs soon after. Low-dose antibiotics are still preemptively fed to
livestock at many CAFOs, since the tight conditions raise the risk of
illness. But antibiotics have caused issues of their own, since
overexposure can breed drug-resistant bacteria. (The FDA issued a draft guidance for industry earlier this year, urging companies to volunteer some reductions.) Manure is also a problem, since it gives off methane and can be washed away by rain, potentially poisoning rivers, lakes or even groundwater. Biotech has also become a big issue for livestock lately, and not just because of cloned cattle: The FDA is mulling a proposal, for example, to allow sales of genetically modified salmon.