Financial Times: In Brazil’s Amazon basin, farmers have long sought out a special form of fertiliser – a locally sourced compost-like substance prized for its amazing qualities of reviving poor or exhausted soils. They buy it in sacks or dig it out of the earth from patches that are sometimes as much as 6ft deep. Spread on fields, it retains its fertile qualities for long periods. They call it the terra preta do indio – literally, “the dark earth of the Indians”. Dense, rich and loamy, this earth …