Sergio González M.1
Two pot-experiments using lucerna plants (Medicago sativa cv. Española) as indicators, were condueted to determine absoluta maximum Cu and Cd upper critical levels and changas in presenee of campost, at La Platina Experimental Station undar uncontrolled greenhouse conditions. Though sensitive to accumulation of both metals in the root growth medium, plants were signilicantly more affected by Cd when the growth medium was pure sand; thus, the absolutes UCL were 4 and 23.5 mg/kg, lor Cd and Cu, respectively. The addition of compost to the root growth medium clearly buffered the phytotoxicity of both metals, showing Cd the highest reduction rateo For this metal, the UCL was increased around 23 times (92.7 mg/kg) whereas the Cu-UCL was increased 9.5 times (225.2 mg/kg). Chemical analysis of harvested tissues revealed that Cu content did not significantly changed, when Cu content in the growth medium increased up to the UCL; this fact was observad either in pure sand and in sand/compost mixture, rellecting no biomagnification of Cu by lucerne plants. Conversely, undar the same conditions, Cd content in green tissues increased several time compared with blank treatments, rellecting high biomagnilication of Cd by lucerne plants.
Key words: Medícago sativa, greenhouse, toxicity, upper critical levels, copper, cadmium, organic compost.
1 Estación Experimental La Platina (INIA), Casilla 439, Correo 3, Santiago, Chile.