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

Progress report for OW20-360

Project Type: Professional + Producer
Funds awarded in 2020: $49,956.00
Host Institution Award ID: G359-20-W7502
Grant Recipient: National Center for Appropriate Technology
Region: Western
State: California
Principal Investigator:
Martin Guerena
National Center for Appropriate Technology
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Project Information

Abstract:

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.  

An additional farm site has been added only for the first experiment as part of an Organic Farming Research Foundation grant that is looking at the same solarization/ biosolarization trials only on certified organic land. 

Project Objectives:

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.  

Timeline:

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

Click linked name(s) to expand/collapse or show everyone's info
  • Alex Ellison - Producer
  • Aldo/Thea Marega/Rittenhouse - Producer
  • Robert & Debbie Ramming - Producer
  • Jim and Karina Knight - Producer
  • Hope/Shayne Sippola/Zurilgen - Producer

Research

Materials and methods:

NCAT’s project will be repeated twice during the two-year period on five different farms. In consultation with the farmers, we will isolate a parcel of land with weedy species present to conduct the experiment. Each farm will have 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 will be 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 should be between 2 to 5 feet between each treatment plot. The statistical test known as analysis of variance (ANOVA) will be used to analyze the data drawn from results of the treatment’s weed stands measured by canopy percentage on these plots. Each property will have 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 will be on a different farm area with the same test design of three test plots, and will 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 will  be continued to be used as the organic matter source for the biosolarization treatment.

We are changing 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 are dominating 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 does rain enough in the winter to grow a cover crop but this is an extreme drought year.  

This way the we will continue to be consistent with the design setup and will be able to compare similar variables replicated in the first year's experiment. Two years of data from the exact experiment would make the results more scientifically solid. The research design will be a randomized complete block design where three replicas of each treatment will be 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 will be broadcast broadcast and then incorporated into the soil.

NCAT will be taking soil samples from each treatment with a shovel at a depth of 6 to 8 inches. Samples will be analyzed for soil organic matter (SOM) content as well as macro and micro-nutrient with A&L Labs of Modesto, CA, and will conduct a phospholipid fatty acid (PLFA) by Ward Labs of Kearny, NE.

Soil tests will be 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 will be recorded on the treatments at the surface, at 3 inches, and 6 inches of the profile. During treatment periods, the farmers will take soil temperatures 2 to 3 times a week. Weed germination will be 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 will be identified by genus and, if possible, species. Special attention will focus on the type of weeds that survived the treatment plots. Weeds will be classified into annuals or perennials, monocotyledons or dicotyledons, cool or warm season weeds.

The 2020 growing season was extraordinary and disrupted many of the farmer's practices. In addition to the COVID-19 pandemic, wild fires, labor availability and drought have effected 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 . 

 

Research results and discussion:

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. 

Combined output graph

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 fieldtrips, 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

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

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

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

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

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

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

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

 

 

 

 

Participation Summary
6 Farmers participating in research

Educational & Outreach Activities

4 Consultations
4 Curricula, factsheets or educational tools
4 Online trainings
4 Webinars / talks / presentations
4 Workshop field days

Participation Summary:

30 Farmers
62 Ag professionals participated
Education/outreach description:

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.

 

 

 

 

Learning Outcomes

4 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation

Project Outcomes

3 Farmers intend/plan to change their practice(s)
1 Grant received that built upon this project
1 New working collaboration
Success stories:

Podcast posted on ATTRA website features farmer Alex Ellison of Castlerock farm describing the effects of the Covid-19 pandemic on marketing and farm planning. Reports preliminary results of solarization and biosolarization trials and own experiment with solarization. 

Other podcast/interviews will be done with some of the farmers collaborating in this study.

Recommendations:

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.  

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.