In the light of these facts, it is apparent that the way in which the cultivation of rice and the problems associated with the left-over stalks is understood, is totally different in more developed countries (United States, Europe) than in Asian countries.

In Asia, the cultivation of rice is an example of sustainability and can be perfectly combined with other productive methods, such as the breeding of fish, duck and livestock. Ducks feed on small fish, other aquatic organisms and algae, whilst the main source of food for buffaloes, bovine livestock, sheep and goats in areas where rice is cultivated is the rice stalk. Rice bran, a by product resulting from the milling of the rice, as well as the low quality grains of rice and surpluses, represent a food supplement for livestock. In turn, the livestock help the farmers with transportation and the preparation of the land: for example, the excrement of the livestock can be recycled to produce organic fertiliser. The rice stalk is also used as a constrction material in the roofing of a multitude of buildings. It is apparent that in this situation, the rice stalk is not a problem.

In developed countries, the situation is different. Animal breeding is much more intensive and demands a high level of economic efficiency from these farms. It could be said that its use is practically nill in monogastric animals, given that the fibrous fraction of the stalk cannot be used. It is inadvisable for it to be included at levels above 30% of the diet, although, in emergency cases it can constitute 100% of the diet. In any case, it is not a very desirable type of fodder and it is generally used as bedding for animals. As well as the low quality of the stalk as a source of nourishment, it is important to point out that frequently, a geographic separation exists between animal producing and rice cultivating industries, making it not worthwhile to transport over long distances such a voluminous material with such a low concentration of nutrients.

Until a short time ago, and due to the limited possibilities of sale of this material, the adopted solution was the burning of the stalks and left-overs of the harvest. As well as being an economical solution, it was believed that through this practice, the ground was disinfected.

The growing awareness of governments faced with environmental probems derived from the burning of rice stalks has resulted in this practice, which produces large quanties of CO2 and health problems in bordering towns, being prohibited nowadays in the majority of European countries and the United States.

Various alternatives exist to the burning of the rice stalks. Those which are most commonly used are as follows:

• 1. The grinding of the stalk and its incorporation into the ground.
• The production of energy either by means of its direct burning and or through the production of biogas as a result of its anaerobic fermentation.
• 1. The production of compost.
• 1. The production of paper pulp.
• 1. The construction of building panels.

From a technical point of view, the alternatives for the mechanisation of the work involved in the removal of the stalk from the fields can be summarised as follows:

• The milling of the stalks and its subsequent incorporation into the ground.
• The baling of the stalks and their withdrawal from the land.

In the case of the Valencian ricefields, the grinding of the stalks and its subsequent incorporation into the ground has mainly been rejected because the stalk does not have sufficient time to decompose in the two months which exist between the harvesting of the crop and the flooding of the fields, giving rise to putrefaction phenomena and odour problems.