Fig. 1
Dose–response curves for effects of humic acids and three plant toxicants on root fresh weight of maize seedlings (data give means of 4 replicates per dose followed by standard deviation). a Humic acids isolated from vermicompost (HA); b sodium chloride (NaCl); c potassium dichromate (K2Cr2O7); d polyethylene glycol (PEG MG 6000). Dashed lines represent the control response level