By Chris Arsenault

ROME (Thomson Reuters Foundation) - Generating three centimeters of top soil takes 1,000 years, and if current rates of degradation continue all of the world's top soil could be gone within 60 years, a senior UN official said on Friday.

About a third of the world's soil has already been degraded, Maria-Helena Semedo of the Food and Agriculture Organization (FAO) told a forum marking World Soil Day.

The causes of soil destruction include chemical-heavy farming techniques, deforestation which increases erosion, and global warming. The earth under our feet is too often ignored by policymakers, experts said.

"Soils are the basis of life," said Semedo, FAO's deputy director general of natural resources. "Ninety five percent of our food comes from the soil."

Unless new approaches are adopted, the global amount of arable and productive land per person in 2050 will be only a quarter of the level in 1960, the FAO reported, due to growing populations and soil degradation.

Soils play a key role in absorbing carbon and filtering water, the FAO reported. Soil destruction creates a vicious cycle, in which less carbon is stored, the world gets hotter, and the land is further degraded.

"We are losing 30 soccer fields of soil every minute, mostly due to intensive farming," Volkert Engelsman, an activist with the International Federation of Organic Agriculture Movements told the forum at the FAO's headquarters in Rome.

"Organic (farming) may not be the only solution but it's the single best (option) I can think of."

(Editing by Ros Russell)