ASSESSING COMPOST PHYTOTOXICITY USING COMPOST ELUATES AND A COMPOST PLATE BIOASSAY

This study compares the Zucconi test (ZT) and a plate bioassay (PB) to assess the possible phytotoxicity of two composts and assesses the possibility to determine the optimal rates of compost amendment to soil using PB. The TZ test was done using Lepidium sativum L., while for the PB test Hordeum vulgare L., Lactuca sativa L. and Lepidium sativum L. were used. The first compost tested came from a treatment plant that processes the organic fraction of solid municipal waste and was regarded to have only low stability (C1), the second was an agro-industrial waste composts with a good maturity index (C2) (Experiment 1). Moreover, the PB using barley and lettuce seeds was done to assess the effects of compost as a soil amendment and to estimate the optimal C2 application dose on an agricultural calcaric Fluvisol soil type (Experiment 2). The results of Experiment 1 show that both ZT and PB are useful for assessing the phytotoxicity of compost and indicate the phytotoxic effects and the positive effects for C1 and C2, respectively. The results of Experiment 2 indicate differences in root elongation and shoot development for both barley and lettuce depending on the dose applied to the soil, showing that PB is sensitive for this test type; in line with this, the results reveal that doses of 2% for barley and 16% for lettuce enhance plant growth. After considering the PB’s simplicity, speed, low cost and sensitivity, we recommend its use with seeds of species like lettuce and/or barley to assess the phytotoxic effects of compost and to estimate the most appropriate application dose.