TESTING LOW-QUALITY URBAN COMPOSTS FOR AGRICULTURE - GERMINATION AND SEEDLING PERFORMANCE OF PLANTS

Two urban composts, one very coarse, low in organic matter but mature, and the other particulated, high in organic matter but not well stabi lized, were tested. Germination 'in vitro' and in soil of cress, ryegr ass and sunflower seeds, seedling performance (root, shoot and sheath lengths) and seedling composition (in soil) of ryegrass were evaluated . Other organic composts, including a vermi-compost, were used for com parison in some experiments. The less mature compost in the 'in vitro' assays showed a strong instant toxicity (despite a low latent toxicit y), expecially when using a sand-compost mixture. Pot trials showed a strong, initial shortening of the primary root of the ryegrass, and al so strong reduction of the mean seedling weight, measured 30 days afte r sowing. In contrast, results with the mature urban compost were exce llent, being similar to those obtained using the vermi-compost. To avo id negative effects on crops, routine germination bioassays should be included in educational programs for farmers. This should enhance mark eting and consumer acceptance of urban composts.