Fodder Crops. Alfalfa (Lucerne)

Many of the world's major crops are grown, at least in part, for animal feed as well as for direct human consumption: maize, wheat, barley, potatoes, soybeans, various root crops, and others. However, there is a wide range of crops cultivated specifically as animal feed.

These include many species of grass and legumes to provide pasture as well as hay and silage, which is fed to housed animals. Such resources have been important since Paleolithic hunter-gatherers manipulated herds of wild animals and began to encourage appropriate browse through the use of fire. As animals were domesticated, beginning around ten thousand years ago, forage species grew in importance and in many regions the use of fire to clear natural vegetation for arable and pastoral agriculture transformed wildscapes into landscapes.

Today, forage crops are vital in the worldwide production of meat, milk, hides, and wool, for human use. They are grown in environments ranging from boreal to tropical, on nutrient-rich and poor soils, at high and low altitudes, and in water-stressed and non-stressed areas. Moreover, forage-producing agroecosystems may be characterized by low energy or high energy inputs.

The more mechanization and chemicals that are employed, the greater the energy input, as these all come from fossil fuels. Pastures comprise areas of naturally occurring grassland with varying degrees of management, or they may be specially planted. The species composition reflects management and environmental constraints. Some species are cosmopolitan; most species are either fast growing or exhibit high productivity.

Many grass species (family Gramineae) are encouraged or cultivated as forage. In tropical/subtropical regions, Sudan grass (Sorghum sudanense) is particularly important whilst in higher latitudes varieties of perennial rye grass (Lolium perenne) and fescue (e.g., tall fescue — Festuca arundinacea and red fescue—Festuca rubra) dominate.

Similarly, many legumes are encouraged in pastures or are cultivated specifically for forage. They are important because they have a symbiotic relationship with specific bacteria with the ability to trap nitrogen from the atmosphere and to convert it to nitrogen compounds that can be used by other organisms, including the legumes. This enrichment of soils with nitrogen encourages overall plant growth and reduces the need of artificial fertilizers.

This capacity has led to the term "green manure" and to the inclusion of leguminous species as forage in many low-latitude agroecosystems that are based on agroforestry — the combination of tree and ground crops that may incorporate forage and/or arable crops. Some forage legumes dominate tropical regions and others temperate environments, but the perennial alfalfa (Medicago sativa), also known as lucerne, and various clovers (Trifolium spp.) are important worldwide.

Both grasses and legumes benefit from management that may include fertilizer applications, crop protection chemicals to reduce unpalatable plant species and insect predators, water conservation in drought-prone areas, and especially the regulation of numbers of grazing animals to avoid pasture degradation and soil erosion.

Alfalfa (Lucerne). Alfalfa is a widespread forage crop because it is highly nutritious, providing protein, vitamins, and minerals for sheep, cattle, and goats. Its history is not well established but it is likely that it was domesticated in Central Asia, possibly Iran, where its wild ancestors were used in abundance. It subsequently spread throughout Europe, and probably to the east. Eventually it was introduced to South America, probably by European colonists after 1500; it then entered North America via California in the late 1800s and subsequently spread north and east.

Today, it is a major forage crop in North America, both in pastures and as a specialty crop for silage as well as the production of meal and pellets. In the latter forms it can be used to supplement silage based on maize and grass.

Alfalfa's value as a forage crop has made it the subject of considerable research. It grows best in well-drained nutrient-rich soils and is most productive when rotational grazing regimes are employed; for example, three days of grazing followed by thirty days of fallow are recommended in temperate environments, though each of the many varieties of alfalfa grows best under specific microconditions. Grazing is not recommended in wet, muddy conditions as crop damage through trampling and uprooting may occur.

Alfalfa benefits from applications of phosphate (a source of available phosphorus), potash (a source of available potassium), and lime (calcium carbonate) to decrease the soil acidity. Before alfalfa is sown, its potential productivity may be enhanced by treating the seed with lime, a fungicide to reduce fungal rot, and an inoculant containing nitrogen-fixing bacteria that will promote root nodulation. A first harvest can usually be achieved between 70 and 90 days, with subsequent harvests every 30 to 38 days; in temperate regions harvests are not possible in winter.

Traditional plant breeding has given rise to numerous varieties of alfalfa but recently attention has focused on genetic modification. A major short-term objective is to produce herbicide-resistant alfalfa so that the effectiveness of weed control using herbicides can be improved without damage to the alfalfa crop; subsequent developments may include improved feed value by promoting protein production and the generation of phytase enzymes to improve phosphorus utilization by animals.

Moreover, the development of aluminum tolerance would bring benefits to the environment and to productivity by curtailing the need for liming aimed at reducing soil acidity—which causes alfalfa to concentrate sufficiently high amounts of aluminum that crop damage occurs.

Prospects for Forage Crops. Competition for land will undoubtedly increase in the next twenty years; population growth and urbanization, especially in developing nations, will encroach onto arable and pastoral land at the same time as food requirements increase. In developed nations, despite land-use diversification involving the encouragement of wildlife conservation, leisure, and tourism activities, meat and animal products will remain significant.

The overall need for increased productivity is an objective that forage grasses and legumes, improved by conventional plant breeding and genetic modification, will provide. Consequently, their importance in world agriculture is likely to remain undiminished.