Field Evaluation of Designed Compost Extracts for Organic Weed Suppression

Organic vegetable growers need practical and cost-effective technology to reduce weed pressure and yield losses. In 2013-2014, OFRF funded Dr. Gladis Zinati at the Rodale Institute to perform laboratory and greenhouse trials on the weed suppressing ability of chemically- and biologically-designed compost extracts (DCE). Dr. Zinati found that DCEs with lower nitrate levels and greater nematode-to-protozoa ratios significantly reduced lambsquarter weed seed germination by 32% without affecting crop seed percent germination. This project builds off of the laboratory and greenhouse work and tests the DCEs in the field. It is essential to assess the efficacy of using DCE on weed suppression, cost savings, and soil health when applied to field-grown vegetable crops as well as report on the germination-inhibitory substances (phenolic compounds and flavonoids) of DCE inhibiting weed seed germination.

The goal of this proposal is to evaluate the impact of using DCE as an alternative tactic, to reduce weed pressure, soil degradation, and yield losses of field-grown organic cabbage crop and the germination-inhibitory compounds of DCE. In a randomized complete block design with four replications, DCE will be applied at two rates and compared to control (water) and hand-weeding and mechanical cultivation (standard farmer’s method). Weed density, biomass, crop yield, harvest index and yield loss in relation to weed density will be determined.

The impact of application rates of DCE on soil health indicators including physical, chemical and biological will be assessed. Concentration of phenolic compounds and flavonoids in compost, DCE and soil will be assessed to determine compounds impacting weed suppression and soil biology. Results will be shared with vegetable growers and interested clientele through Rodale’s Annual On-Farm Field Day, a web article, and presentations at CSA field tours.