Sensitive plants
Producers also face problems in the short term.
Cartel-type behaviour is common in commodity industries, especially in Asia; Thailand, Indonesia and Malaysia recently signed a deal to prop up rubber prices.
But rice is regarded as especially sensitive, since it plays such a vital nutritional role in some of the world's least developed countries.
In Bangladesh, Cambodia and Myanmar, for example, rice accounts for three-quarters of the average supply of dietary energy, and more than two-thirds of protein.
Aid agencies and donors, therefore, are keen to keep rice affordable.
Producer countries, meanwhile, argue that development is best served by paying farmers a profitable price for their crop.