What does it mean? "a third of all homes in China were destroyed to produce fertiliser"?

it means they reused the materials from the homes that were destroyed in order to produce fertiliser...

wood

For a long time wood ash has been used in agricultural soil applications as it recycles nutrients back to the land.

Quote:

For a long time wood ash has been used in agricultural soil applications as it recycles nutrients back to the land.

http://en.wikipedia.org/wiki/Wood_ash

Wood ash is commonly disposed of in landfills, but with rising disposal costs ecologically friendly alternatives are becoming more popular.[6]

For a long time wood ash has been used in agricultural soil applications as it recycles nutrients back to the land. Wood ash has some value as a fertilizer, but does not contain nitrogen. Because of the presence of calcium carbonate it acts as a liming agent and will deacidify the soil increasing its pH.[5]

it means they reused the materials from the homes that were destroyed in order to produce fertiliser...