Rice is the seed of the monocot plant Oryza sativa, of the grass family (Poaceae). As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in tropical Latin America, the West Indies, South Louisiana, East, South and Southeast Asia. It is the grain with the second highest worldwide production, after maize ("corn").. Since a large portion of maize crops are grown for purposes other than human consumption, rice is probably the most important grain with regards to human nutrition and caloric intake, providing more than one fifth of the calories consumed worldwide by the human species. A traditional food plant in Africa, rice has the potential to improve nutrition, boost food security, foster rural development and support sustainable landcare. In early 2008, some governments and retailers began rationing supplies of the grain due to fears of a global rice shortage. The name wild rice is usually used for species of the grass genus Zizania, both wild and domesticated, although the term may also be used for primitive or uncultivated varieties of Oryza. Rice is normally grown as an annual plant, although in tropical areas it can survive as a perennial and can produce a ratoon crop for up to 20 years. The rice plant can grow to 1â€“1.8 m tall, occasionally more depending on the variety and soil fertility. The grass has long, slender leaves 50â€“100 cm long and 2â€“2.5 cm broad. The small wind-pollinated flowers are produced in a branched arching to pendulous inflorescence 30â€“50 cm long. The edible seed is a grain (caryopsis) 5â€“12 mm long and 2â€“3 mm thick. Rice cultivation is well-suited to countries and regions with low labor costs and high rainfall, as it is very labor-intensive to cultivate and requires plenty of water for cultivation. Rice can be grown practically anywhere, even on a steep hill or mountain. Although its parent species are native to South Asia and certain parts of Africa, centuries of trade and exportation have made it commonplace in many cultures worldwide. The traditional method for cultivating rice is flooding the fields while, or after, setting the young seedlings. This simple method requires sound planning and servicing of the water damming and channeling, but reduces the growth of less robust weed and pest plants that have no submerged growth state, and deters vermin. While with rice growing and cultivation the flooding is not mandatory, all other methods of irrigation require higher effort in weed and pest control during growth periods and a different approach for fertilizing the soil. A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact (the most common example would be friction when grains collide). The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations. Thus, the lower size limit for grains in granular material is about 1 Âµm. On the upper size limit, the physics of granular materials may be applied to ice floes where the individual grains are icebergs. Some examples of granular materials are nuts, coal, sand, rice, coffee, corn flakes, fertilizer, and ball bearings. Powders are a special class of granular material due to their small particle size, which makes them more cohesive and more easily suspended in a gas. Granular materials are commercially important in applications as diverse as pharmaceutical industry, agriculture, and energy production. Research into granular materials is thus directly applicable and goes back at least to Charles-Augustin de Coulomb, whose law of friction was originally stated for granular materials. According to material scientist Patrick Richard, "Granular materials are ubiquitous in nature and are the second-most manipulated material in industry (the first one is water)". In some sense, granular materials do not constitute a single phase of matter but have flow characteristics that roughly resemble those of ordinary Newtonian fluids. However, granular materials dissipate energy quickly, so techniques of statistical mechanics that assume conservation of energy are of limited use. Depending on the average energy of the individual grains they may exhibit the properties of solids, liquids, or gases. When the average energy of the individual grains is low and the grains are fairly stationary relative to each other, the granular material acts like a solid. When the granular matter is driven and energy is fed into the system (such as by shaking) such that the grains are not in constant contact with each other, the granular material is said to fluidize and enter a liquid-like state. If the granular material is driven harder such that contacts between the grains become highly infrequent, the material enters a gaseous state. Correspondingly, one can define a granular temperature equal to the root mean square of grain velocity fluctuations that is analogous to thermodynamic temperature.