Evaluating the Effectiveness of Locally Available Woodchips for Weed Control

Final report for FS18-308

Project Type: Farmer/Rancher
Funds awarded in 2018: $9,756.00
Projected End Date: 03/14/2019
Grant Recipient: Farmer
Region: Southern
State: Virginia
Principal Investigator:
Patrick Johnson
NANIH Farm and Garden, Inc.
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Project Information

Abstract:

All farms that have as part of their production system the disturbance of soil will have to manage weeds. Weed control ranks as the number one barrier to organic agricultural production (Kristiansen, Sindel and Jessop, 2007). Farmers practicing more conventional forms of crop production have more tools at their disposal to address weed control than organic farmers. And, while NANIH is not a certified organic grower, we do follow organic and permaculture growing practices. Some of the challenges created by weeds include: competition of light, water, and soil nutrients. Some of the methods of weed control available to organic vegetable growers include: cover cropping, use of herbicides, tillage, solarization, mechanical removal, and various types of mulching. We use no genetically engineered varieties or organisms on our farm.

Moreover, despite the fact that ecologically friendly growing methods, such as organic farming, have grown dramatically over the past 10 years there has been little research done on improving organic and sustainably managed farms’ ability to effectively control weeds. It is estimated that controlling weeds on small, intensely managed farms such as ours can cost as much as 30-50 percent of production costs.

We are proposing to study the effectiveness of using non-chemical means of controlling weeds in market vegetable production. Specifically, we are proposing to use chipped wood mulch to control weeds in small fruit and vegetable production. A study by Olkowski and Klitz (1981) showed that wood chip mulch can be effectively used to significantly reduce weed stands. And, according to a 2007 publication by Chalfer-Scott, the advantages of using wood chips versus plastic mulch include: improved soil structure; enhanced gas transfer; enhance water infiltration and retention; prevention of erosion and compaction; providing nutrients; suppress pathogens and pests; enhanced beneficial organisms; increased biodiversity; neutralize pollutants; reducing economic loss; more visually pleasing produce resulting in increased sales; and ease of application.

Abstract

A study was conducted to evaluate the effectiveness of locally available wood chips as organic mulch for weed control. The study was conducted on an urban farm located in Sandston, Virginia, during the growing period from June 1 through October 1, 2018. The experimental design was set up as a completely randomized design with two mulch treatments and control, replicated 5 times. The experimental plots were approximately 4 ft. by 50 ft. and included single and double shredded hardwood bark applied at a depth of 4 inches; and control (no mulch). Weed infestation was determined by visual observation as well as determining the fresh mass of weed followed by identification of species. A wooden quadrant measuring 0.41 m by 0.41 m (0.168 m²), was used to demarcate random locations on the experimental plots where weed samples were collected. The matric potential and soil temperature were recorded on a weekly basis. All plots were rain-fed with no supplemental irrigation applied. The results revealed that the average weed mass was significantly (p<0.05) higher for the control plots (286 g) compared to those with organic mulches (137g), with the most prevalent weeds species being crabgrass. The visual weed rating showed significantly higher (p<0.05) values for the control plots (62.7%) compared to those treated with mulch (26.5%). There was a linear increase in the weed rating for both control plots (R2=0.89) and those treated with mulch (R2=0.86). There was a correlation between the weed mass and the visual weed rating (r=0.76), suggesting that a relatively direct method of weed assessment (visual rating) would be applicable in estimating the weed mass. The matric head for the plots treated with mulch was significantly lower (more negative) (p<0.05) for the control plots (-7.97 cbar) compared to those with organic mulches (-1.48 cbar). This suggests significantly lower available water for the control plots compared to those treated with mulch. For the soil temperature however, there was no significant difference between the treatments. The yield for okra was significantly (p=0.5) higher for the plots treated with the mulch (2.59 Kgs) compared to the control (2.13 Kgs). We conclude that the locally available wood chips would provide the benefit of weed suppression, improved water holding capacity and hence the yield of okra crop.

 

Project Objectives:

The experimental design will be a completely randomized design with 2 mulch treatments, replicated five times, established on 20 test plots approximately 200 ft.2 The treatments will include blended hardwood mulch applied at a depth of 4 inches; double shredded hardwood bark at a dept of 4 inches; and control (no mulch). All plots will be rain-fed. Multiple vegetables and herbs will be planted including garlic, peppers, onions, zinnias, eggplant, kale, melons, cucumbers, squash, and asparagus. Harvestable and marketable yield for each of these crops will be recorded at harvest time for each experimental plot.

Weed infestation will be determined by monitoring the populations and identification of the species as follows: assigning scores using visual estimates of the observed percentage of weed coverage in each plot; and obtaining a count of the individual weed plants growing in a 1.332 sample area of each plot. We will also identify and record all weed species growing in the plots.

The objectives of the research were as follows:

Using 2 mulch treatments replicated five times on established on twenty test plots approximately 200 ft.² (4000 ft.² total) the project examined the following areas:

Determine differences in weed growth and or suppression in growing beds using wood chip mulch as compared to unmulched control plots;

Determine whether more holding capacity was greater in mulched plots as compared to unmulched control plots;

Determine whether soil temperature was different in mulched plots as compared to unmulched control plots;

Determine whether mulched plot produced greater yields for vegetable, flowers and herbs verses unmulched control;

Determine if there was any difference in weed suppression from using double verse single shredded woodchip mulch;

And finally, identify weed species growing in test plots.

Cooperators

Click linked name(s) to expand
  • Dr. Leanord Githinji (Educator and Researcher)
  • Vernon Heath (Educator)

Research

Materials and methods:

The study on the effectiveness of locally available woodchips for weed control was conducted at NANIH Farm and Garden, located on 37°31’19” North latitude and 77° 19′ 19″ West longitude. The experimental design for this study was a completely randomized design with two mulch treatments and control, replicated 5 times. Thus, a total of twenty experimental plots measuring approximately 4 ft. by 50 ft. or 200 ft.² (4,000 ft.² total) were established.

The treatments included single and double shredded hardwood bark applied at a depth of 4 inches; and Control (no mulch). The four inch thickness was adopted since it was found to be effective in a previous study by Olkowski and Klitz (1981). The treatments included single and double shredded hardwood bark applied at a depth of 4 inches; and control (no mulch). Weed infestation was determined by monitoring the amount and identification of the species. Multiple vegetables and herbs were planted including tomatoes, basil, onions, zinnias, okra, kale, melons, cucumbers, and summer squash. Harvestable and marketable yield for each of these crops were recorded at harvest time for each experimental plot.

Weed infestation was determined by monitoring the population density and identification of the species. Visual rating scores for percentage of weed coverage in each plot were recorded on a weekly basis. In addition, weed samples were collected using a wooden quadrant measuring 0.41 m by 0.41 m (0.168 m²) from each experimental plot. In the laboratory, weed identification was also done and the fresh weight recorded for each sample. The procedure was repeated weekly until 12 weeks for the plots with applied mulch and those without (control plots). In most cases the control plot was situated next to the treated plot with the same vegetable, herb or flower being grown. The data collected for weed mass, visual weed rating, and crop yield were subjected to analysis of variance (ANOVA).

Research results and discussion:

The results for the mass of weeds (g) for the experimental plots with applied organic mulch and those without during the experimental period, are shown (Figure 1). The results revealed that the average weed mass was significantly (p<0.05) higher for the control plots (no mulch) compared to those that with organic mulches. The results for the visual weed rating during the experimental period are shown in Figure 2. Statistical analysis revealed that the weed ratings were significantly higher (p<0.05) for the control plots compared to those treated with mulch. The average ratings for the control plots ranged from 35.1% to 80.5%, with a mean of 62.7%. For the plots treated with mulch, the average ratings ranged from 11.2% to 51.3%, with a mean of 26.5%. For both treatments, the lowest ratings were observed during the first week of the experiment. For the control plots, the highest weed ratings were observed in week 13, while for the treated plots, this was observed in week 12. There was a linear increase in the weed rating for both control plots (R2=0.89) and those treated with mulch (R2=0.86).

The correlation between the weed mass and the visual weed rating was done for the plots treated with mulch (Figure 3). The results revealed a relatively high correlation (r=0.76), suggesting that a relatively direct method of weed assessment (visual rating) would be applicable in estimating the weed mass. The method seems to be applicable for the mulched plots than the control (results not shown), due to the relatively higher variability of the weed species for the latter.

The matric head values for the plots treated with mulch versus the control are shown (Figure 4). The values were significantly (p<0.05) lower, that is more negative, for the control plots (-7.97 cbar) compared to those treated with organic mulches (-1.48 cbar). For the plots treated with mulch, the matric head values increased from -10 cbars to 0 cbars (saturation) during the first 5 weeks. The values remained almost constant at 0 cbars for the rest of the study period, suggesting the soil remained saturated or nearly saturated. For the control plots, there was an increase in matric head values from -10 cbars to -6.9 cbars during the first three weeks. Hence, the value fluctuated between -6.5 to -8.9 cbars through the rest of the experimental period. Matric head is a measure of how tightly the water is bound to the soil matric and hence a measure of how much energy the plant root has to expend to absorb that water. This suggests significantly lower available water for the control plots compared to those treated with mulch.

The yield results for one of the test crops (okra) shows the impact of applying the mulch treatment (Figure 5). This was significantly (p=0.5) higher for the plots treated with the mulch (2.59 Kgs) compared to the control (2.13 Kgs) plots. There was a progressive yield increase from week 1 to week 10, where the maximum yield was observed for either of the control and treated plots. It is apparent that the impact of the mulch treatment was more pronounced later in the season, from the 10th week of the study, compared to the beginning. This could have been as a consequence of the weed pressure increase with time, presenting a stiffer competition for resources (water and plant nutrients) around the 10th week of the study period. We found no difference between double and single shredded mulch in the ability to reduce weed stands. We have visually observed that the double shredded mulch does seem to breakdown decay faster than the single shredded mulch. Mulch-Poster

Weeds Identified in Research Plots

Common Name

Scientific Name

Crab Grass

Digitara sanguinalis

Lamb’s Quarters

Chenopodium berlandieri

Ostrich Ferns

Mattleuccia struthiopteris

Wild Blackberry

Rubus argutus

Greenbriar

Smilax rotundifolia

Dandelion

Taraxacum officinale

Pokeweed

Phytolacca americana

Morning Glory

Ipomoea purpurea

Wood Chips Compared to Plastic Mulch

No good study could be found comparing strictly using plastic mulch for weed control in conventional or organic agriculture. Indeed, the protocol in conventional agriculture for using plastic mulch is to first apply a board spectrum herbicide before laying the plastic on the plot (Ricotta and Masiunas, 1991); (Bonanno, 1996). All organic studied information referring to plastic mulch effects on reducing weed stands only gave vague reference to the ability of plastic mulch to reduce weeds without pointing to any specific study. This lack of information on the use of plastic mulch for weed control could be an area worth future inquiry.

Challenges

We faced a number of problems in implementing this project. First and foremost among the challenges was the weather. 2018 was the second wettest year in recorded history in the Richmond region and the wettest since rainfall totals have been measured at Richmond International Airport (which is one block from the research site). Richmond recorded 68 inches of rain. These rainfall totals had a devastating impact on crop yields, planting dates etc. Indeed, some crops were lost all together due to flooding (tomatoes). The only crop that produced consistent, usable data was okra (one of the few cultivated vegetables that seemed to flourish in wet conditions). The wet conditions also impacted our ability to spread mulch in the research plot. A truck delivering the mulch got horribly stuck and we could not received more mulch deliveries for several months delaying our set of the experimental plots. The experiment ran from June 1st to October 1st for 12 weeks. This weather related delay impacted the usable data we could collect from our test plots. We also experienced animal destruction of our watermelon and cucumber plots. Another challenge was a shortage of labor. It was stated that we would hire two labors. We only found one laborer and had to pay him (Mr. Whitehead) a higher wage as he drove to the site from a considerable distance.

Participation Summary
1 Farmer participating in research

Educational & Outreach Activities

20 Consultations
1000 Curricula, factsheets or educational tools
1 Journal articles
1 Online trainings
3 Webinars / talks / presentations
1 YouTube video post on using wood chip mulch.

Participation Summary

200 Farmers
100 Ag professionals participated
Education/outreach description:

Our education and outreach plan as put forth in our proposal involved on farm education, the use of social media, and attending various sustainable agriculture regional conferences hosting table at each.

The following chart outlines the activities and number of people engaged by each. Please note that the received information denotes people who actually talked to Patrick and or received a printed description of the project.

Event/Activity

Date

Number Attend.

Number Engaged

Received Inform.

Mulch Video

1/19

14

14

14

On Farm Events

0

0

0

Carolina Farm Stewardship Association

11/18

800

500

100

Black Urban Farmers and Gardens

10/18

300

70

70

Virginia State Small Farm Conference

11/18

200

100

100

Hispanic Farmers Conference

12/18

200

30

30

Future Harvest CASA

1/19

700

25

25

Virginia Biological Farm Association

1/19

400

200

100

Southern SAWG Conference

1/19

1200

700

250

Virginia Beginning Farms and Ranchers Coalition

3/19

20

20

20

Total Engagement

 

3,834

1659

709

Due to wet conditions present at our farm throughout the growing season in 2018 we decided not to hold any on farm activities out of safety concerns. Our strategy with concern to social media was to post a general mulching video that would inspire people to visit our website were they could view our mulch research information. We posted our video on YouTube and only received 14 views (well below the 1000 views we had hope). By far our greatest outreach and engagement outreach success was achieved through information tables and a poster display of our research presented at the Southern SAWG Conference. We far and away exceeded the number of conference we had proposed attending in our proposal (4 vs. 7). The feedback we received was generally positive concerning our research.

Learning Outcomes

20 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key changes:
  • Knowledge about using wood chips specifically how to apply wood chips for best results for controlling weeds.

  • Also, some farmer fear of creating a nitrogen sink or loss when using wood chips were reversed or eased.

Project Outcomes

3 Farmers changed or adopted a practice
1 New working collaboration
Project outcomes:

This project has contributed to agricultural sustainability by demonstration that there are affordable and effective alternative to plastic mulching for small scale natural and organic farms for weed control. Locally available hardwood mulch not only control weeds, when properly applied, but also help with water retention, and can help increase production of vegetable crops. The lead research has an ongoing relationship with Virginia State University thus will be able to inform farmers of these important findings.

Recommendations:

No good study could be found comparing strictly using plastic mulch for weed control in conventional or organic agriculture. Indeed, the protocol in conventional agriculture for using plastic mulch is to first apply a board spectum herbicide before laying the plastic on the plot (Ricotta and Masiunas, 1991); (Bonanno, 1996). All organic studied information referring to plastic mulch effects on reducing weed stands only gave vague reference to the ability of plastic mulch to reduce weeds without pointing to any specific study. This lack of information on the use of plastic mulch for weed control could be an area worth future inquiry.

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.