Monoculture, a method of growing one crop in a field annually, is generally considered to be unsustainable due to the outside resources required to maintain annual growth. Such resources include the use of chemical pesticides and synthesized fertilizers. Monocultural farming methods can also deplete the land of other natural resources and increase the salinity of the soil, rendering a field unfit for further farming.

Pesticides, though sometimes necessary in the short term, can harm the soil food web, a complex ecology of micro-organisms in soil that helps sustain the plant from the roots down. Experiments comparing plants grown in soil compared to plants grown through hydroponics have shown a thirty-three percent higher growth rate when there are beneficial soil microorganisms available.

Certain pesticides synthesized by chemical companies can impart a sometimes fatal toxicity to humans, livestock and insect pollinators, such as bees and butterflies, which may be necessary for plant success. Without insect pollinators, farm labor must be expended to manually pollinate each plant. Crops such as cacao beans and vanilla are examples of crops requiring highly labor-intensive practices in the absence of natural pollinators.

Throughout history, farmers seeking to grow crops usually confine themselves to growing only the fastest and most productive plants. Such practices can result in growing crops without the genetic diversity found in wildlife. Without such diversity in the genes, crops may become more susceptible to disease and crop failure. The Irish potato famine is a well-known example of the dangers of monocultural and mono-varietal crop cultivation.

Many scientists, farmers, and businesses have debated how to make agriculture farming sustainable. One of the many practices includes growing a diverse number of perennial crops in a single field, each of which would grow in separate season so as not to compete with each other for natural resources. This system would replicate the biodiversity already found in a natural environment, resulting in increased resistance to diseases and decreased effects of erosion and loss of nutrients in soil. Nitrogen fixation from legumes, for example, used in conjunction with plants that rely on nitrate from soil for growth, will allow the land to be reused annually. Legumes will grow for a season and replenish the soil with ammonium and nitrate, and the next season other plants can be seeded and grown in the field in preparation for harvest. This method is considered to require a minimal amount of outside resources.

In practice, there is no single approach to sustainable agriculture, as the precise goals and methods must be adapted to each individual case.

Cite: Wikipedia