Farming tradition has often included the sharing and trading of seed varieties among farmers. 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. In drier areas, farmers may irrigate their fields. Fertilizers must be formulated so that their nutrients are easily absorbed by crops.
Manure is animal excrement, and compost is decomposed organic matter, usually from plants.
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. 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. There are some natural pesticides, such as neem, a substance that has been used for centuries in India.