Sustainable agriculture

• DEFINITION: The growing and harvesting of crops in a manner that has minimal impact on the environment

The practices associated with sustainable agriculture help to protect the environment by preventing soil loss through erosion; minimizing the use of pesticides and chemical fertilizers, which can cause water pollution; conserving water; and enriching nutrient-depleted soils.

Most twentieth-century agricultural practices were based on continued economic growth. This practice demonstrated dramatic increases in production but had negative impacts on the environment through the losses of plant and animal habitats, depletion of soil nutrients, and pollution of water supplies. The concept of sustainable development focuses on the use of renewable resources and working in harmony with existing ecological systems. The World Commission on Environment and Development described sustainable development as the ability “to meet the needs of the present without compromising the ability of future generations to meet their own needs.” Practitioners of sustainable agriculture strive to manage their agricultural activities in such a way as to protect air, soil, and water quality, as well as conserve wildlife habitats and biodiversity.

Sustainable agriculture tries to match crops and livestock to the topography, soil characteristics, and climatic conditions that exist in a given region. The crops selected for cultivation must be well suited to the existing soil and site conditions and should also be resistant to known pests in the area.

Problems Caused by Agriculture

Water pollution was one of the most damaging and widespread effects of modern agriculture in the early twenty-first century. The runoff from farms accounted for the majority of sediment damage to natural waterways in the early 2020s, and the chemicals and nutrients associated with this runoff in the United States were estimated to cost billions of dollars per year to clean. Heavy application of nitrogen fertilizers, insecticides, and herbicides raised the potential for groundwater contamination. Feedlots that concentrate manure production led to further groundwater contamination. In 2021, several of the most commonly used pesticides—atrazine (11 percent), hexazinone (7.8 percent), prometon (6.4 percent), and tebuthiuron (6.0 percent)—were detected in the groundwater of 41 percent of US wells. In addition, monoculture, or the growing of a single crop on an area of land, requires heavy reliance on agricultural chemicals because the practice of growing the same crop repeatedly depletes the natural organic nutrients that were formerly rich in North American topsoils.

Research has found that many of the chemical agents, pesticides, fertilizers, plant-growth regulators, and antibiotics used in agriculture have ended up in the food supply. These chemicals can be harmful to humans at moderate doses, and chronic effects can develop with prolonged at lower doses. Further, widespread pesticide use has been shown to result in severe stress in other animal populations, including bees. Pesticide use is often followed by occurrences of secondary pest outbreaks and resurgence of pests that have developed to the pesticides previously used.

Because of these growing problems, many American farmers have turned to the practices associated with sustainable agriculture. The US government offers guidance for this transition through the Food, Agriculture, Conservation, and Trade Act of 1990. This legislation describes sustainable agriculture as agriculture that, through an integrated system of plant and animal production practices, can, over the long run, meet human food and fiber needs, enhance environmental quality and natural resources, make the most efficient use of nonrenewable resources, maintain economic viability of farm operations, and enhance the quality of life for farmers and society.

Water Conservation and Soil Conservation

In the western United States, the ability to irrigate crops is an especially important factor in agriculture, as much of the region is naturally arid or semiarid. In California, the limited supply of has caused overdraft of groundwater and the consequent intrusion of saltwater, which causes the permanent collapse of aquifers. In order to counteract such negative effects, sustainable farmers in California have introduced improved water conservation and storage methods, selecting drought-resistant crop species, using reduced-volume systems, and managing crops to reduce water loss. Drip and trickle irrigation methods also dramatically reduce water usage and water loss while helping to avoid such problems as soil salinization.

Farmers can temporarily manage salinization and contamination of groundwater with pesticides, nitrates, and selenium by using tile drainage to remove water and salt. This method often has adverse effects on the environment, however. Long-term solutions include conversion from the planting of row crops to production of drought-tolerant forages and the restoration of wildlife habitats.

One of the most important aspects of sustainable agriculture is soil conservation. In order to prevent excessive erosion, farmers might leave grass strips in the waterways of their fields to capture soil that begins to erode. A field with a 5 percent slope has three times the water runoff volume of a field with a 1 percent slope and eight times the soil erosion rate. Contour plowing, which involves plowing across a hill rather than up and down the hill, helps capture overland flow and reduce water runoff. Contour plowing is often combined with strip farming, where different kinds of crops are planted in alternating strips along the contours of the land. As one crop is harvested, another is still growing and helps recapture wind- and waterborne soil while preventing runoff from flowing quickly downhill. In areas of heavy rainfall, sustainable farmers might construct tiered ridges to trap water and prevent runoff. This method involves a series of ridges that are constructed at right angles to one another to direct runoff and slow it down so that the water has a chance to soak into the soil.

Another farming method that contributes to soil conservation is terracing, in which the land is shaped into level shelves of earth to hold in water and soil. Soil-anchoring plants are grown on the edges of the terraces to provide further stability for the soil. Terracing is costly, but it can enable farmers to grow crops on steep hillsides that they otherwise could not use for production. To protect fragile or unstable soil on sloping sites or along waterways, farmers may need to plant perennial species of grasses every year.

Livestock and Animal Manure

Ruminant animals (sheep, cattle, and goats) can be raised on rangeland, pasture, cultivated forage, cover crops, shrubs, weeds, and crop residues. The breeds that have lower growth and milk production potential can adapt better to environments with sparse or seasonal forage. By growing row crops on level soil and growing pasture on steeper slopes, farmers can help reduce soil erosion; growing pasture and forage crops in rotation can help improve soil quality. When ruminants and other farm animals are allowed to graze in pasture lands, those fields are fertilized naturally. Farmers can direct how their fields are fertilized with animal manure by using portable fencing to keep livestock grazing in one area or strip of pasture all the way down before moving the animals to another strip of the field while the first strip of pasture recovers.

Sustainable farmers also use so-called green manure—crops that are raised specifically to be plowed under—to introduce and nutrients into the soil. Green manure crops help protect against erosion, cycle nutrients from lower levels of the soil into the upper layers, suppress weeds, and keep nutrients in the soil rather than allowing them to leach out. Legumes such as sweet clover, ladino clover, and alfalfa are excellent green manure crops. They are able to extract nitrogen from the air into the soil and leave a supply of nitrogen for the next crop that is grown. Some crops, such as beans and corn, can cause high soil erosion rates because they leave the ground bare most of the year. One way sustainable farmers combat this is by leaving crop residues on the land after harvest. Residues help reduce soil erosion and even excessive soil temperatures in hot climates. Many farmers choose to use cover crops rather than residue crops. The decision about which to grow is based on the farm’s geographical location and the purpose of the crop: to control erosion, to capture nitrogen for the soil, to nitrogen to the crop, or to improve soil structure and suppress weeds.

Cover Crops

Cover crops such as hairy vetch or clover are well suited to the needs of later crops with high nitrogen requirements, such as tomatoes or sweet corn. Both of these cover crops decompose and release nutrients into the soil within one month. To fight erosion, a farmer might choose a fast-growing cover crop, such as rye. Rye provides abundant and an extensive root system that can prevent soil erosion and capture nutrients. Alfalfa, rye, or clover can be planted after harvest to protect the soil and add nutrients and can then be plowed under at planting time to provide a green manure for the crop. Cover crops can also be flattened with rollers, and seeds can be planted in their residue. This gives the new young plants a protective cover and discourages weeds from overtaking them. Use of natural nitrogen also reduces the of water contamination by agricultural chemicals.

Sustainable agriculture emphasizes the use of reduced tillage systems, which are intended to disturb the soil as little as possible when preparing it for planting. Minimum-till farming involves using the disc of a chisel plow to make a trench in the soil where seeds are planted. Plant debris is left on the surface of the ground between the rows, which helps prevent erosion. Conservation tillage, or conser-till farming, uses a cutting tool (a coulter) attached to a plow to open slots in the ground just wide enough to insert seeds without disturbing the soil. No-till planting involves drilling seeds into the ground directly through any ground cover or mulch.

Crop Rotation and Monoculture

Planting the same crop every year on a given field can result in depleted soil. In order to keep the soil fertile, practitioners of sustainable agriculture rotate nitrogen-depleting crops (such as sweet corn, tomatoes, and cotton) from year to year with legumes, which add nitrogen to the soil. By planting winter cover crops, such as rye grass, farmers can protect their land from erosion. Such cover crops will, when plowed under, provide nutrient-rich soil for the planting of cash crops. Crop rotation also improves the physical condition of the soil because the different crops vary in root depth and in the ways they are cultivated.

In nature, various kinds of plants grow in mixed meadows, and this helps them to avoid insect infestations. The agricultural practice of monoculture places great quantities of the food of choice in easy proximity to insect predators. Insect populations that feed on particular crops can multiply more than they otherwise would when those crops are grown in the same fields year after year. Since most insects are instinctively drawn to the same home area every year, they cannot proliferate and thrive if their crops of choice are not in the same fields every year.

In addition to helping farmers use fewer pesticides, crop rotation helps to control weeds naturally. Some crops and cultivation methods inadvertently allow certain weeds to thrive. Sustainable farmers often incorporate into their crop rotations successor crops that eradicate weeds. Some crops, such as potatoes and winter squash, work as cleaning crops because of the different style of cultivation that is used on them. Pumpkins planted between rows of corn will help keep weeds at bay.

Integrated Pest Management

Most sustainable farmers control insect pests through a practice known as integrated pest management (IPM). In IPM, each crop and its pests are evaluated as an ecological system. A plan is developed to manage the damage that pests can do through the use of particular cultivation techniques, biological methods, and chemical methods at different timed intervals. IPM techniques are effective, profitable, and safe and have been adopted for crops such as tomatoes, citrus, and apples.

The goal of IPM is to keep pest populations below the size where they can cause damage to crops. Fields are monitored to gauge the level of pest damage. If farmers begin to see crop damage, they put cultivation and biological methods into effect to control the pests; physical techniques such as vacuuming bugs off crops are also used. IPM encourages the growth and diversity of beneficial organisms that enhance the defenses and vigor of plants. Small amounts of pesticides are used only if all other methods fail to control pests. It has been found that IPM, when done properly, can reduce inputs of fertilizer, lower the use of irrigation water, and reduce pre-harvest crop losses by up to 50 percent. Reduced pesticide use can cut the costs of pest control significantly and, if done properly, can increase crop yields without increasing production costs. As governments around the world implemented legislation limiting the use of pesticides and banning the use of particular chemicals, pesticide use decreased substantially during the twenty-first century. However, by the 2020s, while the use of pesticides had decreased, the use of herbicides had increased. This is largely attributed to the prevalence of genetically engineered seeds, which were introduced in 1996 by agrochemical giant Monsanto and which were capable of surviving being sprayed with much higher doses of herbicides than other seeds.

Sustainable farming advocates continued to push for policies that included increased support for organic farming and help for more farmers to adopt sustainable practices. In the US, the Agriculture Resilience Act, introduced in Congress in 2020, aimed to address climate change by giving farmers the tools needed to tackle that crisis. In light of the growing concerns of climate change in the twenty-first century, such legislation was deemed essential to the planet's future health.

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