Abstract

Cadmium (Cd) in soil could enter human body via food chain contamination. Farmers regularly apply manure to the vegetable growing fields in the up-country in Sri Lanka. Regular manure application could increase concentration of labile C in soil, which could maintain relatively high soluble Cd fraction in soil, resulting soil Cd more bioavailable. A pot experiment was conducted in a greenhouse with soils (Ultisols) collected from an urban vegetable garden in Seethaeliya, Sri Lanka to assess whether the manure application affects the phytoavailability of soil Cd to lettuce. Lettuce was grown for three consecutive crop cycles with and without cattle manure. For one manure-added treatment, dried manure was added as a bulk (i.e. one time at the beginning of the first crop at the rate of 75g of manure per 5kg of soil in fresh weight basis) and as a split dose for the other treatment at the rate of 25g of manure per 5 kg of soil at the beginning of every crop. The concentration of total Cd was 0.72 mg/kg in soil and 0.60 mg/kg in cattle manure. Only 2% of total Cd was easily extractable in soil, whereas 21% of total Cd in the manure was easily extractable. Concentration of Cd in lettuce was significantly higher in manure-added treatments compare to the unamended soil. Manure application (both bulk and split) increased Cd concentration in lettuce. Incorporation of easily extractable Cd and increase of labile C via manure application may have contributed to elevate Cd concentrations in lettuce.