Solarization and Biosolarization: Harnessing the Sun and Organic Matter to Control Weeds

View the project final report

Commodities

• Vegetables: greens (leafy), peppers, tomatoes

Practices

• Education and Training: on-farm/ranch research
• Pest Management: integrated pest management, soil solarization

Biosolarization is a relatively new innovation in the realm of weed control. Similar to solarization, which uses clear plastic sheeting on moist soil to thermally terminate a variety of pest species, biosolarization includes the use of organic matter in the form of compost, cover crops, manure or other organic materials such as pomace or nut hulls.  The addition of organic matter accelerates the process by encouraging anaerobic soil disinfestation. The carbon from organic material produces chemicals with bio-pesticidal activity. This results in the release of chemicals combined with the heat which acts like a fumigant during the solarization process. 

The primary objective of the project is to measure the efficacy of biosolarization on weedy species present on five farms in northern California. Biosolarization will have achieved the objective if the plots with treatments have significantly reduced weed populations, both in absolute number, species present and duration of the treatment, compared to plain solarization and the control plots.  

NCAT will replicate the experiment twice over a two-year period on five separate farm properties. Each property will have three test plots with three separate treatments within each plot, a solarized section, a biosolarized treatment using compost the first year and a cover crop in the second year, and a control. The biosolarized treatment will last 8-10 days after incorporating the organic matter and the solarized sections treatment will take 32 days, which is the minimum recommended time for solarization in the Central Valley.  

Our first objective is to test the relative effectiveness of solarization, biosolarization, and control plots on farms in Northern California. NCAT will work with five farms to measure the effectiveness of the three treatments on weed seed germination and species mix. The first-year treatment plots will include untreated, solarized, and biosolarized (with compost) plots. The second year will include untreated, solarized, and a cover crop for the biosolarized plots. We will have succeeded if we can show that biosolarization can effectively reduce weed populations compared to controls and take less time to implement, but with similar efficacy against weeds, than solarization. A farmer will be able to take the information gained from this experiment and make a well-informed decision as to whether or not biosolarization is a viable practice for their farm. 

Our second objective is to look at the feasibility in terms of incorporating standard practices such as cover cropping and the addition of compost as the source of organic matter in the biosolarized plots.  Timing of biosolarization and solarization with each farm’s scheduled seeding or transplanting of the multiple crops grown by the participating farmers will be evaluated. 

The third objective is to publicize the results.  In working with five farmers, NCAT hopes to better understand the effects of biosolarization in five areas with different soils, cropping systems, and pest pressures.  Assuming a positive outcome, these localized trials will help to encourage the adoption of biosolarization in these regions.  The results will be published and highlighted on our widely read sustainable farming website (www.attra.ncat.org). We will also produce a webinar to highlight the results of this effort and have an on-farm field day both years of the project.  We are hoping to show how biosolarization can be added to the short list of effective sustainable weed control practices.