PHENOLIC-ACIDS AS POTENTIAL SEED GERMINATION-INHIBITORS IN ANIMAL-WASTE COMPOSTS

A laboratory experiment was conducted to investigate the presence of phenolic acids in some animal-waste composts as well as their biological activity on the germination of sorghum (Sorghum bicolor Moench) seeds. Nine samples of composts, three in each group of cattle-, chicken-, and hog-waste composts, were extracted with deionized water at the rates of 10, 40, and 80 g L-1. The seeds were imbibed in deionized water or respective compost extracts for 4 h. The content of water soluble phenolic acids in the compost extracts showed a negative correlation with the water uptake (r = -0.88**), a-amylase activity (r = -0.82**), and subsequent germination % (r = -0.81**) of sorghum seeds. The germination-inhibitory effects of the composts were observed in the acidic fraction of the compost extracts which contained the phenolic acids. The commercial phenolic acid preparations reduced the germination of sorghum seeds at a higher concentration (> 50 mg L-1) than the total phenolic acid content estimated in the composts. It was considered that the phenolic acids may be a major group of germination-inhibitory substances in animal-waste composts. The possibility of synergistic effects of phenolic acids in the germination-inhibitory composts was indicated. The presence of non-phenolic germination-inhibitors in the composts was also demonstrated.