Evaluating the Effectiveness of Locally Available Woodchips for Weed Control

View the project final report

Commodities

Practices

• Pest Management: mulching - vegetative, weed ecology
• Production Systems: organic agriculture
• Soil Management: organic matter
• Sustainable Communities: urban agriculture

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.

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.