Phytotoxicity and detoxification of fresh coir dust and coconut shell

Phytotoxicity and detoxification of fresh coir dust and milled coconut shell were studied using lettuce bioassay, phytotoxin analysis and incubation with liming and other amendments at different temperatures. Fresh coir dust and fresh fine coconut shell severely inhibited root elongation of lettuce. The phytotoxicity was attributed to the phenolic compounds in the substrates and the higher concentration of water-soluble phenolic compounds in the finer substrates aggravated the phytotoxicity. The critical concentration of phenolic compounds toxic to lettuce root growth was found to be about 2 mg L-1. Fresh coir dust and coconut shell could be detoxified by incubation. Liming and elevated incubation temperature significantly increased the processes of detoxification.