Biochemical properties of compost extract produced by composted green waste and its effect on the growth of Dahlia pinnata Cav., Consolida ajacis (L.) Schur, and Centaurea cyanus L

This study looked at the effects of different extraction protocols on the biochemical properties of compost extract (CE) and its effect on the growth of Dahlia pinnata Cav. (dahlia), Consolida ajacis (L.) Schur (delphinium), and Centaurea cyanus L. (cornflower). Composted green waste (CGW) extract was prepared at compost-to-water ratios of 8:1, 8:2, 8:3, and 8:4, employing preservation methods of sterilization and refrigeration, or direct refrigeration. Sterilized CE with compost-to-water ratio of 8:3 exhibited superior biochemical properties (pH value, electrical conductivity, nutrient contents, and enzyme activities). The stem width, root length, flower number, root-shoot ratio, and total chlorophyll contents of dahlia cultivated in the optimal CE significantly increased by 33%, 44%, 115%, 110%, and 28%, respectively; the stem width, root length, flower number, root-shoot ratio, and total chlorophyll content of delphinium in the optimal CE greatly increased by 39%, 25%, 76%, 31%, and 31%, respectively; the stem width, root length, flower number, root-shoot ratio, and total chlorophyll content of cornflower in the optimal CE remarkably increased by 29%, 27%, 108%, 44%, and 17%, respectively. Therefore, the results indicated that CE at a compost-to-water ratio of 8:3, coupled with sterilization and refrigeration effectively promoted plant growth, offering a superior alternative to CGW.