Compost Recipe Development and Weed Seed Viability Evaluation with Cranberry Leaves

A small-pile demonstration study was conducted to evaluate the possibility of composting cranberry leaves on commercial cranberry farms in Southeastern Massachusetts. The recipe ratios tested were: 20:0:0 (cranberry leaves only), 10:10:2, and 10:10:1 (leaves:horse manure and bedding:fish hydrolysate). Both mixed recipes generated thermophilic temperatures (between 43-66°C for at least 20 d), conditions known to destroy many plant pathogens and weed seeds. Analysis of leaf samples indicated that all three recipes were more acidic than most other types of compost (values below pH 6). Nitrogen levels were at or below the low-end (0.45-0.75% N) of the typical level seen with most compost (1% N). The final C:N ratios (22:1 to 38:1) were within the acceptable range for many uses. The mixed piles attained thermophilic temperatures for sufficient duration to prevent germination of the seven species of weeds tested. Leaf residue levels for eight common cranberry pesticides were also determined. The insecticide, chlorpyrifos, and the metabolite of the herbicide dichlobenil, BAM (2,6-dichlorobenzamide), were detected at levels below food tolerance and slightly above the food tolerance threshold, respectively. These levels were within a range that would allow the pursuit of commercial development of the compost since ingestion is not an anticipated end-product use. The data from this preliminary demonstration study would suggest that the composted product would be acceptable for use on-farm as well as for distribution to other off-farm sites, but additional replicated research studies are warranted.