Farmers rely heavily on inputs, natural or man-made resources that allow them to grow, cultivate and harvest crops, or to breed animals. Inputs can be very costly and a farmer must usually go into debt to acquire them, on the hope that the farm's earnings will be sufficient to repay the debt, and, hopefully, provide a profit. To succeed, a farmer must learn techniques to use and manage these resources, such as land, soil, seed, and water, in the best way possible. Inputs include:
- land: maximizing a limited amount of land is important. Farmers sometimes own their own land, or they may lease it. In controlled economies, such as the former Soviet Union, farmers may work collectively on state-owned lands.
- soil: tilling (breaking up) and conditioning the soil with manure or compost can help activate beneficial organisms in the soil, reduce erosion, provide readily-absorbed nutrients and increase production.
- seed: seed can be "natural" (or "heirloom"), hybrid, or genetically manipulated (GM). Natural seed is often taken from a portion of a farmer's own crops. Farming tradition has often included the sharing and trading of seed varieties among farmers. Hybrids are a cross of 2 or more crop varieties selected for their positive growing characteristics (such as short growing season, or resistance to heat, cold, or disease). Hybrid seeds are sterile, and must be purchased. Genetically manipulated seeds are made by the very complex processes of splicing genetic material from one plant species onto that of another.
- water: plants need sufficient water to grow. In drier areas, farmers may irrigate their fields.
- fertilizers: fertilizers are synthetic (chemical) sources of nutrients (usually nitrogen, phosphorous, and potassium, designated with the chemical symbols N, P, and K, respectively) that help plants grow faster and stronger. Fertilizers must be formulated so that their nutrients are easily absorbed by crops.
- manure (or other soil conditioners, such as compost): manure and compost condition and provide nutrients for the soil. Manure is animal excrement, and compost is decomposed organic matter, usually from plants.
- labor: farming is very labor-intensive work, but it has also traditionally been one of the lowest-paying economic sectors. On family farms, labor has always been provided by family members, but larger commercial farms often use hired labor. When farm workers are too scarce, or labor costs are too high, farmers will often mechanize.
- machinery: in recent decades, the trend all over the world has been for young farm workers to move to the cities to find better-paying work. The result has been a shortage in farm laborers. Machinery, such as tractors, plows, harvesters, threshers, and balers help farmers automate mundane, back-breaking work.
- pesticides: pesticides are chemical insect killers that often have toxic effects on soil and water, as well as animals, farm workers, and consumers. There are some natural pesticides, such as neem, a substance that has been used for centuries in India.
- herbicides: herbicides are chemical plant killers. They are used to kill weeds that compete with crops for root space, nutrients, and water. Sometimes the unintentional effect of using herbicides is to kill the plants they were intended to save. Long-term use of herbicides (as well as pesticides and fertilizers) leads to pollution of soil and ground water.
