CAFF’S On-Farm Occultation Research Report

Research and recommendations on occultation

Building on our work in biointensive no-till systems, CAFF’s Climate Smart Farming team launched a research trial on California vegetable farms on a related practice called occultation. Occultation or “weeding with tarps”, is considered an important weed management tool for biointensive no-till systems and is increasingly used in small-scale organic vegetable production. This practice typically involves irrigating a field or bed and laying down a thick, black plastic tarp for 2-8 weeks. Under the tarp, the weed seeds germinate in the warm, moist environment, then die due to lack of sunlight, and decompose back into the soil. While more and more small farms are using occultation to manage weeds and improve soil tilth in no-till and low-till systems, there has been little formal research into the practice.

CAFF partnered with five farms in Northern and Central California to answer the following questions:

1. What effect does occultation have on the amount of labor needed to manage weeds in a bed?

2. What effects does occultation have on the weed pressure and weed types (broadleaf vs. grass) in a bed?

3. What effect does occultation have on vegetable quality (weight, marketability, etc.)?

4. What effect does occultation have on carrot/beet yield (based on root weight)?

In addition, CAFF looked at benefits and tradeoffs related to occultation. To learn more about this project, including research results and advice from the farmers we collaborated with, you can access our On-Farm Occultation Trial Report below. To hear directly from First Rain Farm and Super Tuber Farm about how they use occultation, check out our Farmer’s Beet podcasts here!