Synthetic nitrogen, along with mined rock phosphate, pesticides and mechanization, have greatly increased crop yields in the early 20th century.
Its increasing price and scarcity (global price of rock phosphate rose 8-fold in the 2 years to mid 2008) could change global agricultural patterns.
An initial application of rock phosphate has kept the system going for many years.
It expects to supply 411,200 tons of granulated rock phosphate to local fertilizer manufacturers within the next five years.
About 39% of the revenue is generated from the transportation of petroleum, 19% from imported wheat, fertilizer and rock phosphate.
A lease to mine rock phosphate on the islands was obtained by Charles Broadhurst in 1884.
Other organic fertilizer sources could be seaweed, fishmeal, manures and rock phosphate.
The world's total economic demonstrated resource of rock phosphate is 18 Gt, which occurs principally as sedimentary marine phosphorites.
"In the tropics we use rock phosphate because it is cheaper," he said.
Recently the term peak phosphorus has been coined, due to the limited occurrence of rock phosphate [1] in the world.