Final report for OW20-360
Project Information
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 replicated the experiment twice over a two-year period on five separate farm properties. Each property had three test plots with three separate treatments within each plot: a solarized section, a biosolarized treatment using compost, and a control. The biosolarized treatment lasted 8-10 days after incorporating the organic matter and the solarized sections treatment took 32 days, which is the minimum recommended time for solarization in the Central Valley.
An additional farm site was added only for the first experiment as part of an Organic Farming Research Foundation grant that evaluated the same solarization/ biosolarization trials only on certified organic land.
Our first objective was to test the relative effectiveness of solarization, biosolarization, and control plots on farms in Northern California. NCAT worked with five farms to measure the effectiveness of the three treatments on weed seed germination and species mix. The two-year treatment plots included untreated, solarized, and biosolarized (with compost) plots. We will have succeeded if we 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 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 was 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 have been published and highlighted on our widely read sustainable farming website (www.attra.ncat.org). We also produced a webinar to highlight the results of this effort and had virtual field days both years of the project. We demonstrated how biosolarization can be added to the short list of effective sustainable weed control practices.
|
Spring 2020 |
Announcement of awards |
|
Summer 2020
|
Take initial soil samples Place plastic sheeting on solarized plots Twenty days into the solarization and apply compost and plastic sheeting on biosolarized plot Monitored soil temperatures. Thirty days after solarization and ten days into biosolarization plastic is removed Second soil samples taken Cool season crop planted |
|
Fall 2020
|
Emerged weeds evaluated with Canopeo App and weeds identified Third sets of soil samples taken Record weed control activity Monitor harvest Plant cover crops for second experiment on biosolarized plots |
|
Winter 2021 |
Evaluate data and write report of results Monitor germination of cover crops |
|
Spring 2021
|
Monitor cover crops and determine time to terminate the cover crop Prepare area for second experiment, take soil samples Terminate cover crop and take biomass measurements Place plastic sheeting on solarized plots for thirty days Place plastic on biosolarization treatment with terminated cover crop for ten days |
|
Summer 2021
|
Plastic is removed Soil samples are taken Emerged weeds are evaluated with Canopeo App Summer crop planted Weed control activity monitored Third sets of soil samples taken and submitted Harvest weighed from treatments |
|
Fall 2021 |
Continue monitoring harvests from all plots Outline and design webinar Conduct webinar Develop and edit video Post video on website and social media |
|
Winter 2022 |
Update and edit publications Develop and submit report results |
Cooperators
- - Producer
- - Producer
- - Producer
- - Producer
- - Producer
Research
NCAT’s project was repeated twice during the two-year period on five different farms. In consultation with the farmers, we isolated a parcel of land with weedy species present to conduct the experiment. Each farm had a total experimental area of .01 acres equivalent to 435 sq. ft. This measurement was chosen because it lends itself well to extrapolation in terms of costs and application of organic matter. Each treatment plot size was approximately 5’ X 9.67’ X 9 plots = 435.15 sq. ft. per block; the equivalent to 0.01 acres. Depending on the farm layout and equipment used on these farms there was between 2 to 5 feet between each treatment plot. The statistical test known as analysis of variance (ANOVA) was used to analyze the data drawn from results of the treatment’s weed stand measured by canopy percentage on these plots. Each property had three test plots with three separate treatments within each block: 1 plot for control with no treatment; 1 plot for solarization with plastic cover for 32 days; 1 plot for biosolarization with 5 tons/acre equivalent of compost and covered with plastic for 8-10 days.
In year two, the experiment was on a different farm area with the same test design of three test plots, and include three separate treatments within each: 1 plot for control with no treatment; 1 plot for solarization with plastic cover for 32 days; 1 plot for biosolarization with 5 tons/acre equivalent of compost and covered with plastic for 8-10 days. We had planned to use a cover crop seeded at 100 lbs. /acre equivalent of seed planted (20% brassica, 40% vetch 40% triticale, brome or Sudan grass) with plastic cover for 8-10 days but due to insufficient rainfall and lack of supplemental irrigation, compost was used as the organic matter source for the biosolarization treatment.
We changed the experimental design from cover crops to compost as the organic matter source for the biosolarization trial because the planted cover crop did not get sufficient rain to germinate and grow. We planted the cover crop in November expecting the winter rains to germinate and carry the crop through spring. As of April 4, Sacramento valley has only received 40% of normal rainfall to date. Only 7 inches instead of 17. The cover crop was planted at twice the seeding rate (equivalent of 200 lbs. / Acre) in the 48 sq ft of treatment plots. The resulting stand is stunted and the plant numbers very sparse due to being fed on by birds and rodents as it was germinating. The weeds growing on the treatment plots dominated the remanence of the cover crop. So in order to continue the spring trials, compost was the backup organic matter source. Few of the farms we are working with irrigate their cover crops in the winter so we assumed we would follow this practice. In normal years it rains enough in the winter to grow a cover crop but this was an extreme drought year.
This way the we continued to be consistent with the design setup and were able to compare similar variables replicated in the first year's experiment. The research design was a randomized complete block design where three replicas of each treatment were assigned randomly to three blocks. The materials necessary for this project include clear U.V. resistant 3 mil plastic, soil temperature gauges and compost . The compost was broadcasted and then incorporated into the soil.
NCAT took soil samples from each treatment at a depth of 6 to 8 inches. Samples were analyzed for soil organic matter (SOM) content as well as macro and micro-nutrient with A&L Labs of Modesto, CA, and conducted a phospholipid fatty acid (PLFA) test by Ward Labs of Kearny, NE.
Soil tests were conducted on all plots comparing treatments to the control. Ward Labs note that the PLFA test is, “conducted by analyzing phospholipid fatty acids, or PLFA. PLFA is a snapshot of soil community structure and abundance at the time of sampling. As environmental conditions such as temperature and moisture change so does the microbial community. Soil temperatures were recorded on the treatments at the surface, at 3 inches, and 6 inches of the profile. During treatment periods, the farmers and assistants took soil temperatures 2 to 3 times a week. Weed germination was evaluated by comparing the control plot’s canopy to the three treatment areas using the Canopeo mobile application that is a green canopy cover measurement tool developed by Oklahoma State University. This app tracks the growth of crops by calculating fractional green canopy cover through pictures or video. Its operation is based on calorimetry, offering real time results in a natural setting that is much more accurate than visual examinations. After a picture or video has been taken, the application displays the results on the smart phone. The image can be uploaded, filling out different data to identify the sample. The kind of weeds that emerge in the control were identified by genus and, if possible, species. Special attention focused on the type of weeds that survived the treatment plots. Weeds were classified into annuals or perennials, monocotyledons or dicotyledons type of weeds.
The 2020 growing season was extraordinary and disrupted many of the farmer's practices. In addition to the COVID-19 pandemic, wildfires, labor availability and drought have affected many of the farms where these trials were located. The first trials were executed on all the farms but the subsequent planting and management changed on some of them. This will be detailed in the results and discussion section .
The first trial conducted on six farms across Northern California from August 13 to October 13, 2020 produced the following results:
When results from all six blocks of the study were combined and analyzed together, a strong association between weed control treatment used and percent vegetative cover (weed germination) was found. The two-way ANOVA revealed that overall, the relationship between percent vegetative cover and type of weed control treatment was significant, F (2,36) = 54.14, p = .0001, partial η2 = .750. However, farm location had a significant effect on the percent vegetative cover observed as well: F(5,36) = 63.04, p = .0001, partial η2 = .897, and the two-way ANOVA also revealed a significant interaction effect between farm location and weed control treatment F(10,36) = 9.86, p = .00001, partial η2 = .733, signifying that the effect of weed control treatment on percent vegetative cover was dependent upon the farm sampled.
Because farm location and weed control treatment both had a significant effect on percent vegetative cover, and because there was a significant interaction effect between these two factors, we cannot extrapolate these findings beyond the farms that we sampled to arrive at general conclusions. However, we can conclude that for the farms sampled in this study, weed control treatment did have a significant effect on the percent vegetative cover (weed germination) that we observed. Bonferroni post hoc tests revealed that plots receiving the control weed treatment (no weed control) had an average of 17.5% more vegetative cover than did solarized plots (95% CI, 11.7 to 23.40), which was a statistically significant difference (p = .0001). Plots receiving the control weed treatment (no weed control) had an average of 23.2% more vegetative cover than did biosolarized plots (95% CI, 17.39 to 29.08), which was also a statistically significant difference (p = .0001).
There was no significant difference in percent vegetative cover observed between solarized and biosolarized plots (p = .059), however, the reductions in percent vegetative cover achieved by biosolarization occurred in roughly a quarter of the time that it took for solarization to achieve. More studies are needed to determine under which landscape contexts solarization and biosolarization are viable weed control practices, but our study suggests that biosolarization is indeed an effective and quick way to control weeds in a significant way.
Marginal Means of % Vegetative Cover
The following section presents the results obtained from each individual farm, including the one-way analysis of variance results from each individual farm, the measured treatment temperatures, and the weed identification details.
Fiery Ginger Farm is a 2 acre urban farm located in West Sacramento, California that provides a variety of vegetables, vegetable and flower transplants, eggs and meats. They also have an educational component where they host school field trips, participate in classroom lessons and support Future Farms of America programs in West Sacramento and Davis California. They sell to school districts, farmers markets and community supported agriculture (CSA). Because of the pandemic they had to adjust to the school districts closing, some farmers markets discontinuing and their CSA adapted and developed a Grab and Go Box concept where CSA type boxes are sold as is at farmers markets or customers pick them up at the farm. As a result, monitoring yields of products from treated areas was not possible. The farmer was able to monitored and record temperatures.
Average temperature readings-2020.
|
Treatment |
Surface |
3 Inches |
6 Inches |
|
Solarization (8-13 to 9-10) |
111oF |
102oF |
94oF |
|
Biosolarization (8-13 to 8-20) |
119oF |
107oF |
98oF |
Weeds identified:
|
Common Name |
Scientific Name |
Family |
Category |
|
Henbit |
Lamium amplexicaule |
Lamiaceae |
Broadleaf |
|
Common Purslane |
Portulaca oleracea |
Portulacaceae |
Broadleaf |
|
Common Chickweed |
Stellaria media |
Caryophyllaceae |
Broadleaf |
|
Redroot Pigweed |
Amaranthus retroflexus |
Amaranthaceae |
Broadleaf |
|
Burclover |
Medicago polymorpha |
Fabaceae |
Broadleaf |
|
Annual Grasses |
Poa annua Hordeum jubatum Avena fatua |
Poaceae |
Grass |
|
Nutsedge |
Cyperus spp |
Cyperaceae |
Sedge |
|
Shepherd’s purse |
Capsella bursa-pastoris |
Brassicaceae |
Broadleaf |
Trial results
A strong association between weed control treatment used and percent vegetative cover (weed germination) was found; the one-way ANOVA revealed that the relationship between percent vegetative cover and type of treatment was significant, F (2,6) = 27.53, p = .00095. Post-hoc t-tests revealed that weed germination was significantly higher in the control treatment as compared to both plots treated with the solarization treatment (p= 0.012), and plots treated with the biosolarization treatment (p = 0.003). Plots treated with the biosolarization treatment also had significantly lower weed germination rates than did plots treated with solarization alone (p = 0.0077).
Polestar Farm is a 12 acre organic orchard near Esparto, gateway to the Capay Valley. They produce a variety of stone fruits, citrus and figs. Biosolarization is of interest to the proprietors because of the possibility to grow strawberries and vegetables between the fruit trees to diversify their products. The pandemic postponed this project but the trials continued for observation purposes. Located in an orchard, the treatments were shaded in the morning and afternoon yet the temperatures were high enough to have an effect on the treatments. This farm was near wildfires that had days of hazy/smoky conditions during the trials.
Average temperature readings-2020.
|
Treatment |
Surface |
3 Inches |
6 Inches |
|
Solarization (8-17 to 9-14) |
114oF |
106oF |
101oF |
|
Biosolarization (8-17 to 8-27) |
114oF |
110oF |
107oF |
Weeds identified
|
Common Name |
Scientific Name |
Family |
Category |
|
Persian Speedwell |
Veronica persica |
Scrophulariaceae |
Broadleaf |
|
Field Bindweed |
Convolvulus arvensis |
Convolvulaceae |
Broadleaf |
|
Hairy Vetch |
Vicia villosa |
Fabeae |
Broadleaf |
Trial results
A strong association between weed control treatment used and percent vegetative cover (weed germination) was found; the one-way ANOVA revealed that the relationship between percent vegetative cover and type of treatment was significant, F (2,6) = 12.67, p = .0071. Post-hoc t-tests revealed that weed germination was significantly higher in the control treatment as compared to both plots treated with the solarization treatment (p= 0.027), and plots treated with the biosolarization treatment (p = 0.019). Plots treated with the biosolarization treatment were not significantly different from plots treated with solarization alone (p = 0.103).
Gauchito Hill Farm is a ten acre certified organic farm located in Capay Valley, California. They grow a variety of organic fruit and vegetables, which can be found at several Bay area farmers' markets, grocery stores, online grocery retailers and restaurants. Due to the pandemic Gauchito farm altered their planting schedule and decided not to plant winter vegetables which included land where the trials were set up. Wildfires prevented access to the farm for a week and conditions were hazy and smoking during that time. The treatment was not irrigated after since vegetables were not being considered.
Average temperature readings-2020.
|
Treatment |
Surface |
3 Inches |
6 Inches |
|
Solarization (8-28 to 9-25) |
116oF |
99oF |
91oF |
|
Biosolarization (8-28 to 9-7) |
100oF |
84oF |
88oF |
Weeds identified
|
Common Name |
Scientific Name |
Family |
Category |
|
Sow Thistle |
Sonchus oleraceus |
Asteraceae |
Broadleaf |
|
Field Bindweed |
Convolvulus arvensis |
Convolvulaceae |
Broadleaf |
|
Velvetleaf |
Abutilon theophrasti |
Malvaceae |
Broadleaf |
|
Redroot Pigweed |
Amaranthus retroflexus |
Amaranthaceae |
Broadleaf |
Trial results
No significant association between weed control treatment used and percent vegetative cover (weed germination) was found; the one-way ANOVA revealed that the relationship between percent vegetative cover and type of weed control treatment was not significant, F (2,6) = 2.91, p = .131.
Full Belly Farm is a well-known established organic farm in the Capay Valley. The field where the experiments were carried out was thought to be planted with flowers after the trials were conducted. It turned out it was seeded with a cover crop of Sudangrass, buckwheat and field peas. We decided to continue with the trials and treat the cover crop as a weeds which if they are allowed to go to seed they can be.
Average temperature readings-2020.
|
Treatment |
Surface |
3 Inches |
6 Inches |
|
Solarization (9-4 to 10-2) |
121oF |
109oF |
93oF |
|
Biosolarization (9-4 to 9-14) |
123oF |
108oF |
90oF |
Weeds identified
|
Common Name |
Scientific Name |
Family |
Category |
|
Sow Thistle |
Sonchus oleraceus |
Asteraceae |
Broadleaf |
|
Field Bindweed |
Convolvulus arvensis |
Convolvulaceae |
Broadleaf |
|
Redroot Pigweed |
Amaranthus retroflexus |
Amaranthaceae |
Broadleaf |
|
Cheeseweed |
Malva parviflora |
Malvaceae |
Broadleaf |
|
Bristly Ox Tongue |
Picris echioides |
Asteraceae |
Broadleaf |
|
Yellow Starthistle |
Centaurea solstitialis |
Asteraceae |
Broadleaf |
|
Nutsedge |
Cyperus spp |
Cyperaceae |
Sedge |
|
Sudangrass |
Sorghum bicolor |
Poaceae |
Grass |
|
Buckwheat |
Fagopyrum esculentum |
Polygonaceae |
Broadleaf |
|
Field Pea |
Pisum sativum |
Fabeae |
Broadleaf |
Trial results
A strong association between weed control treatment used and percent vegetative cover (weed germination) was found; the one-way ANOVA revealed that the relationship between percent vegetative cover and type of treatment was significant, F (2,6) = 15.87, p = .004. Post-hoc t-tests revealed that weed germination was significantly higher in the control treatment as compared to both plots treated with the solarization treatment (p= 0.04), and plots treated with the biosolarization treatment (p = 0.00017). Plots treated with the biosolarization treatment were not significantly different from plots treated with solarization alone (p = 0.164).
Pacific Star Garden is a u-pick produce, berries and stone fruit operation with a roadside stand located south of Woodland California. Most of the planted vegetable and berry ground is irrigated by buried drip which provided excellent distribution of water for the trials.
Average temperature readings-2020.
|
Treatment |
Surface |
3 Inches |
6 Inches |
|
Solarization (8-28 to 9-25) |
114oF |
102oF |
92oF |
|
Biosolarization (8-28 to 9-7) |
118oF |
108oF |
96oF |
Weeds identified
|
Common Name |
Scientific Name |
Family |
Category |
|
Milk Thistle |
Sonchus oleraceus |
Asteraceae |
Broadleaf |
|
Field Bindweed |
Convolvulus arvensis |
Convolvulaceae |
Broadleaf |
|
Mustard |
Brassica spp. |
Brassicaceae |
Broadleaf |
|
Redroot Pigweed |
Amaranthus retroflexus |
Amaranthaceae |
Broadleaf |
|
Lambsquarter |
Chenopodium album |
Chenopodiaceae |
Broadleaf |
|
Annual Grasses |
Poa annua Hordeum jubatum Avena fatua |
Poaceae |
Grass |
Trial Results
A strong association between weed control treatment used and percent vegetative cover (weed germination) was found; the one-way ANOVA revealed that the relationship between percent vegetative cover and type of treatment was significant, F (2,6) = 111.86, p < .0001. Post-hoc t-tests revealed that weed germination was significantly higher in the control treatment as compared to both plots treated with the solarization treatment (p= 0.00045), and plots treated with the biosolarization treatment (p = 0.00045). Plots treated with the biosolarization treatment were not significantly different from plots treated with solarization alone (p = 0.974).
Castle Rock Farm is a small market farm, which began its adventure in 2018 on a 4.9 acre parcel located at the base of Mt. Diablo in beautiful Walnut Creek, California. It started as a roadside stand and started to supply restaurants in the area. The pandemic changed many of the marketing plans and they now are focusing on CSA and continued sales at the Farmstand. As is the case with other collaborators, areas where trials were carried out were not planted because of the reduced market.
Average temperature readings-2020.
|
Treatment |
Surface |
3 Inches |
6 Inches |
|
Solarization (8-19 to 9-22) |
116oF |
97oF |
92oF |
|
Biosolarization (8-19 to 8-26) |
113oF |
95oF |
89oF |
Weeds identified
|
Common Name |
Scientific Name |
Family |
Category |
|
Curly Dock |
Sonchus oleraceus |
Asteraceae |
Broadleaf |
|
Field Bindweed |
Convolvulus arvensis |
Convolvulaceae |
Broadleaf |
|
Purslane |
Brassica spp. |
Brassicaceae |
Broadleaf |
|
Nutsedge |
Amaranthus retroflexus |
Amaranthaceae |
Broadleaf |
|
Purslane |
Portulaca oleracea |
Portulacaceae |
Broadleaf |
|
Annual Bluegrass |
Poa annua
|
Poaceae |
Grass |
Trial Results
No association between weed control treatment used and percent vegetative cover (weed germination) was found; the one-way ANOVA revealed that the relationship between percent vegetative cover and type of treatment was not significant, F (2,6) = 2.28, p = .183.
Soil Quality Results Across All Farms 2020
Soil samples were taken from each treatment on each farm to measure the effect of biosolarization and solarization on soil quality metrics. A randomized complete block design one-way analysis of variance was undergone to determine if three different weed control methods had an effect on total biomass, diversity index, % bacteria, total bacterial biomass, total fungi %, total fungi biomass, fungi : bacteria ratio, nitrate levels (ppm), %K, and % OM throughout the various plots. No significant differences between treatments for any of the variables were found (p > .05 for all variables). Other research by Fernandez-Bayo et al. (2017) and by Achmon et al. (2020) found changes in bacterial and fungal soil microbiome components during biosolarization. For these trials, logistics in traveling to multiple farms, timing in sampling the treatments, accessibility to farms (wildfires), shipping to laboratories (cold shipment for phospholipid fatty acids (PLFA) tests and time taken to analyze the sample at the lab may have affected the results. For the second trial soil sampling protocols will be re-evaluated.
|
Variable |
Numerator DF |
Denominator DF |
F |
p-value |
|
Total Biomass |
2 |
15 |
0.955 |
0.41 |
|
Diversity Index |
2 |
15 |
2.12 |
0.15 |
|
Bacteria % |
2 |
15 |
2.89 |
0.09 |
|
Total Bacteria Biomass |
2 |
15 |
3.22 |
0.07 |
|
Total Fungi % |
2 |
15 |
2.02 |
0.17 |
|
Total Fungi Biomass |
2 |
15 |
3.03 |
0.08 |
|
Fungi: Bacteria Ratio |
2 |
15 |
1.54 |
0.25 |
|
Nitrate ppm |
2 |
15 |
0.10 |
0.91 |
|
K% |
2 |
15 |
0.71 |
0.51 |
|
OM% |
2 |
15 |
0.21 |
0.82 |
The second trial conducted on five farms across Northern California from April 28 to July 9, 2021. Unfortunately, one of the farms tilled the trials before they were evaluated leaving four farms to collect data from. When results from all four farms of the study were combined and analyzed together using a one-way ANOVA, a strong association between the type of weed control treatment used and the percent vegetative cover (weed germination), or canopy, was found. The one-way ANOVA comparing weed treatment type across all four farms was significant, F (2,33) =27.3, p<.001, partial η2=0.623. A two-way ANOVA comparing the combined effect of weed treatment and farm location on vegetative cover also revealed a significant interaction, F (5,30) = 29.084, p <.001, partial η2= 0.6233, suggesting there is an interaction effect between farm location and weed treatment.
A Bonferroni post-hoc test comparing the effects of weed treatments across all farms showed that, on average, there was a difference in vegetative cover between plots receiving the control treatment (i.e. no weed control) and plots receiving solarization treatment of 48 percentage points (F (2,6), p <.001, CI= 29.7, 66.5). Similarly, the average difference in vegetative cover between control plots and plots receiving biosolarization treatment was 45 percentage points (F (2,6), p<.001, CI= (26.9, 63.8)). The average difference in vegetative cover observed between biosolarization plots and solarization plots was not significant (p = 1.0). These results suggest that solarization and biosolarization are equally effective treatments for reducing weed cover.
Estimated Marginal Means of Percent Vegetative Cover 2021
Castle Rock
Average temperature readings-2021.
| Treatment | Surface | 3 inches | 6 inches |
| Solarization (5/26 to 6/30) | 120oF | 107.5oF | 98.25oF |
| Biosolarization (5/26 to 6/4) | 116oF | 100oF | 92oF |
Weeds identified:
| Common Name | Scientific Name | Family | Category |
| Cheeseweed | Malva parviflora | Malvaceae | Broadleaf |
| Field Bindweed | Convolvulus arvensis | Convolvulaceae | Broadleaf |
| Lambsquarter | Chenopodium album | Chenopodiaceae | Broadleaf |
| Sow thistle | Sonchus oleraceus | Asteraceae | Broadleaf |
| Mustard | Brassica spp. | Brassicaceae | Broadleaf |
Trial Results
A strong association between weed control treatment used and percent vegetative cover (weed germination) was found on the Castle Rock farm; the one-way ANOVA revealed that the relationship between percent vegetative cover and type of treatment was significant, F (2,6) =150.1, p<.001. Post-hoc Bonferroni tests revealed a significant average difference in percent vegetative cover between control plots and both plots receiving solarization (p<.001) and plots receiving biosolarization (p<.001) treatments. Plots receiving solarization treatment and those receiving biosolarization treatment did not have a significant difference in vegetative cover (p=1).
Fiery Ginger
Average temperature readings-2021.
| Treatment | Surface | 3 inches | 6 inches |
| Solarization (5/10 to 6/10) | 114.75oF | 104oF | 93.25oF |
| Biosolarization (5/10 to 5/20) | 113oF | 100oF | 86oF |
Weeds identified:
| Common Name | Scientific Name | Family | Category |
| Nutsedge | Cyperus spp. | Cyperaceae | Sedge |
| Spurge | Euphorbia maculata | Euphorbiaceae | Broadleaf |
| Pigweed | Amaranthus spp. | Amaranthaceae | Broadleaf |
| Groundsel | Senecio vulgaris | Asteraceae | Broadleaf |
| Sow thistle | Sonchus oleraceus | Asteraceae | Broadleaf |
| Crabgrass | Digitaria spp. | Poaceae | Grass |
Trial Results
No significant association between weed control treatment used and percent vegetative cover (weed germination) was found on the Fiery Ginger farm; results from the one-way ANOVA showed no significant difference in vegetative cover among any of the three treatment types (F (2,6) =.495, p=.632). These results could be in part due to the trials being transplanted with cucumbers immediately after the plastic for the solarized treatment was removed. When the Canapeo reading were taken, the cucumber transplants had grown enough to cover most of the beds making them indistinguishable from the weeds.
Gauchito
Average temperature readings-2021.
| Treatment | Surface | 3 inches | 6 inches |
| Solarization (5/12 to 6/10) | 132oF | 120.3oF | 105oF |
| Biosolarization (5/12 to 5/21) | 118oF | 114oF | 102oF |
Weeds identified:
| Common Name | Scientific Name | Family | Category |
| Field Bindweed | Convolvulus arvensis | Convolvulaceae | Broadleaf |
| Crabgrass | Digitaria spp. | Poaceae | Grass |
Trial Results
A strong association between weed control treatment used and percent vegetative cover (weed germination) was found on Gauchito farm; the one-way ANOVA revealed that the relationship between percent vegetative cover and type of treatment was significant, F (2,6) =8.47, p=.0179. Post-hoc Bonferroni tests revealed a significant average difference in percent vegetative cover between control plots and plots receiving solarization (p=.0234) treatment. There was no significance observed between plots receiving biosolarization treatment compared to either the control plots (p=1) or those receiving solarization treatment (p=1).
Pacific Star
Average temperature readings-2021.
| Treatment | Surface | 3 inches | 8 inches |
| Solarization (4/28 to 6/10) | 132oF | 114oF | 103oF |
| Biosolarization (4/28 to 5/5) | 130oF | 119oF | 102oF |
Weeds identified:
| Common Name | Scientific Name | Family | Category |
| Nutsedge | Cyperus spp. | Cyperaceae | Sedge |
| Cheeseweed | Malva parviflora | Malvaceae | Broadleaf |
| Lambsquarter | Chenopodium album | Chenopodiaceae | Broadleaf |
| Field Bindweed | Convolvulus arvensis | Convolvulaceae | Broadleaf |
| Pigweed | Amaranthus spp. | Amaranthaceae | Broadleaf |
| Crabgrass | Digitaria spp. | Poaceae | Grass |
Trial Results
A strong association between weed control treatment used and percent vegetative cover (weed germination) was found on the Pacific Star farm; the one-way ANOVA revealed that the relationship between percent vegetative cover and type of treatment was significant, F (2,6) =188.9, p<.001. Post-hoc Bonferroni tests revealed a significant average difference in percent vegetative cover between control plots and both plots receiving solarization (p<.001) and plots receiving biosolarization (p<.001) treatments. Plots receiving solarization treatment and those receiving biosolarization treatment did not have a significant difference in vegetative cover (p=1).
Soil Quality Results Across All Farms 2021
Soil samples were taken at each control and treatment plot on each farm to measure the effect of biosolarization and solarization on soil quality metrics. A randomized complete block design one-way ANOVA was used to determine if a significant difference in soil quality metrics was observed among the control and two different weed control treatments. The soil qualities that were sampled for included total biomass, diversity index, % bacteria, total bacterial biomass, total fungi %, total fungi biomass, fungi: bacteria ratio, nitrate levels(ppm), %K, and % OM. No significant differences in soil quality were observed among the control and two treatments for any of the variables measured (p>.05 for all variables). A table of these results is shown below.
| Variable |
Numerator DF |
Denominator DF | F | p-value |
| Total biomass | 2 | 9 | 0.229 | 0.8 |
| Diversity Index | 2 | 9 | 1.104 | 0.373 |
| Bacteria % | 2 | 9 | 0.998 | 0.406 |
| Total bacteria biomass | 2 | 9 | 0.879 | 0.448 |
| Total fungi % | 2 | 9 | 0.775 | 0.489 |
| Total bacteria biomass | 2 | 9 | 0.719 | 0.513 |
| Fungi: bacteria | 2 | 9 | 0.253 | 0.782 |
| OM % | 2 | 9 | 1.085 | 0.378 |
| Nitrate ppm | 2 | 9 | 1.216 | 0.341 |
| K % | 2 | 9 | 0.114 | 0.894 |
Conclusion and Discussion
The overall results from both trials demonstrated that there was a significant difference between the control weed treatment (no weed control) and the biosolarized and solarized treatment in the late summer / early fall and in the late spring / early summer seasons of the Sacramento Valley. The difference in weed control between biosolarization plots and solarization plots was not significant. These results suggest that solarization and biosolarization are equally effective treatments for reducing weed cover except that the solarized treatment took longer (an average of 30 days) compared to the biosolarized treatment (an average of 9 days) in California’s Sacramento Valley. This difference in treatment time is crucial for farmers with tight planting schedules trying to fit their production to coincide with desire markets. The reduction of weeds will also have a decrease in weeding costs and may improve yields.
Additional studies on the secession of weed species following biosolarization is recommended. This would determine the impact on the weed seed bank over time and the effects of these treatments on the weed species’ lifecycle. Perennial weeds such as nutsedge (Cyperus spp.) and field bindweed (Convolvulus arvensis) were not dramatically affected by these biosolarization/ solarization trials. Due to the growth characteristics of these weeds and the narrow five feet wide beds of the treated areas, their emergence may have originated from propagules outside the treatment area. Since these trials were conducted with strip plastic sheeting covering a five-foot-wide bed, perhaps using complete coverage sheeting which consists of a continuous surface over the entire field to be planted may affect these perennial weeds. Using complete coverage will also treat the furrow area which is untouched in strip coverage and may reduce the need to repeat treatment every season.
Research Outcomes
Education and Outreach
Participation Summary:
Due to Covid-19 restrictions on farm demonstrations and field days have been cancelled and most outreach efforts has been through virtual workshops at 4 conferences. The following video is a presentation in Spanish for the Ecological Farming Association conference done on January 23, 2021. It is located on the EcoFarm Conference site on Vimeo and will be posted on the ATTRA website. An English version of this presentation will be recorded and also posted on the ATTRA website.
Similar presentation in Spanish with simultaneous English translation was done for the Tilth Alliance Conference on November 10, 2020. This presentation can be found on Tilth Alliance's You Tube page: https://www.youtube.com/watch?v=lvL2Y5DRIc0&list=PLvYjukikPLv7g2WP_eVOr4F9Spqz-e8Fk&index=4
A Spanish language presentation for the Latino Farmer Conference on February 11, 2021 New Innovations in Weed Management featured a significant segment on Biosolarization as well as preliminary results from this research. This will be posted on the ATTRA webpage.
A presentation for the Small Farm Conference on February 15, 2021, title Biointensive Integrated Pest Management was conducted in Spanish and which also features a brief description of solarization and biosolarization and presented results of this research. This video will be posted on the ATTRA webpage.
Organic Weed Control Field Day on August 6, 2022 at Agriculture and Land Based Training Association (ALBA) in Salinas California. Biosolarization and Solarization trial establishment by participants as well as additional weed control methods.ACAM_CA_FIELDDAYDRAFT2mbk_7.15.22
Education and Outreach Outcomes
First trials are complete. Evaluating the plan and strategy for second trial sometime in April -May 2021. Once the second trial is complete and compared with the results of the first trial, a better picture will emerge on successes, shortfalls and areas of further study.
The overall results from both trials demonstrated that there was a significant difference between the control weed treatment (no weed control) and the biosolarized and solarized treatment in the late summer / early fall and in the late spring / early summer seasons of the Sacramento Valley. The difference in weed control between biosolarization plots and solarization plots was not significant. These results suggest that solarization and biosolarization are equally effective treatments for reducing weed cover except that the solarized treatment took longer (an average of 30 days) compared to the biosolarized treatment (an average of 9 days) in California’s Sacramento Valley. This difference in treatment time is crucial for farmers with tight planting schedules trying to fit their production to coincide with desire markets. The reduction of weeds will also have a decrease in weeding costs and may improve yields.
Additional studies on the secession of weed species following biosolarization is recommended. This would determine the impact on the weed seed bank over time and the effects of these treatments on the weed species’ lifecycle. Perennial weeds such as nutsedge (Cyperus spp.) and field bindweed (Convolvulus arvensis) were not dramatically affected by these biosolarization/ solarization trials. Due to the growth characteristics of these weeds and the narrow five feet wide beds of the treated areas, their emergence may have originated from propagules outside the treatment area. Since these trials were conducted with strip plastic sheeting covering a five-foot-wide bed, perhaps using complete coverage sheeting which consists of a continuous surface over the entire field to be planted may affect these perennial weeds. Using complete coverage will also treat the furrow area which is untouched in strip coverage and may reduce the need to repeat treatment every season.