Abstract
Effect of drying method as a pretreatment of compost samples on the test results and their causes were examined, when plant growth inhibition by animal waste compost was evaluated by germination tests in petri dishes. The plant inhibition of extraction liquid from compost was investigated by using the elongation of the root of Komatsuna (Brassica campestris L.). 1) Germination tests were carried out to evaluate the plant growth inhibition of cattle feces, hog feces, chicken manure and their composts treated with draft drying at 50℃ and freeze-drying. Some samples, especially pig feces and its compost after draft drying showed lower plant inhibition than the undried samples. On the contrary, when the freeze-dried samples were used, the results of the germination test were similar to those for the non-dried samples. Draft drying causes a larger decrease in lower fatty acids, phenolic acids and ammonium nitrogen in the samples than freeze-drying. When the results of the germination test were different according to the drying methods, there were considerable differences in lower fatty acids, ammonium nitrogen and electric conductivity of the aqueous extracts of the compost. 2) Germination tests using solutions with lower fatty acids, phenolic acids and ammonia were carried out. Within the analysis values in extraction liquid of the compost used in above-mentioned experiment, lower fatty acids showed the most remarkable plant inhibition. 3) Germination tests and analysis of components were done on the fractionation of aqueous extract of pig feces which was divided by gel chromatography. The fractions which showed plant inhibition contained high levels of lower fatty acids. Also a highly negative correlation was observed between the elongation of the root of Komatsuna and lower fatty acid concentrations. 4) In conclusion, freeze-drying seemed to be a desirable method of drying samples for evaluating plant growth inhibitory of the animal waste compost by germination test, because it can decrease the loss in volatile phytotoxic substances represented for lower fatty acid.
