Organic weed management using chemically and microbially designed compost extracts
Organic vegetable growers, such as Aimee and John Good, are interested in effective weed management techniques that allow them to reduce the frequency of in-season cultivation to manage weed pressure while, enhancing soil health and crop yields. Partnering with the Goods, an experimental and demonstration field trial was established in Kutztown, Pennsylvania in July 2016 to evaluate the effectiveness of chemically- and microbially-designed compost extract (CMD-CE) on weed management in cabbage, lettuce and turnip during the fall season. In a randomized complete block design with four replications, CMD-CE was applied either post-planting of the crop or pre- and post-planting of the crop and compared to the grower’s standard treatment (in-season cultivation). A no treatment (no cultivation or compost) was included.
Preliminary results showed that soil bulk density did not vary with treatments except in the cabbage plots where compost extracts reduced compaction. Weed dry biomass was reduced by 43% and 38% when compost extract was applied as a post-planting treatment and as pre- and post-planting treatment on the turnip beds, respectively. A similar pattern was observed in the cabbage beds. However, in the lettuce beds weed biomass was lowest only when compost extract was applied before and after planting. Statistical analyses of weed diversity and density, crop yield, and soil chemical and biological analyses are underway. So far, project results have been shared with 218 people in person and nearly 100,000 people via social media – Facebook (44k likes), Twitter (48.3k followers), and Instagram (7.5k followers).
An on-farm trial was conducted at Kutztown, PA in the fall of 2016 to demonstrate the impact of chemically- and microbially- designed compost extract (CMD-CE) on soil health, crop yield, and weed pressure. In a randomized complete block design with four replications, we established three vegetable crops – cabbage, lettuce and turnip – with four treatments – post-planting CMD-CE application, pre- and post-planting CMD-CE, in-season cultivation (standard), and no cultivation or compost application. Soil, weed pressure, and crop yields were evaluated. Aimee and John Good provided soil cultivation, preparation of beds and in-season cultivation (for Grower’s standard treatment).
Weeds density, biomass, and diversity were assessed. Soil physical properties were measured at Rodale Institute in samples collected from each treatment. Additional sets of soil samples were collected and sent to commercial laboratories for chemical and biological assessments. Vegetable crops were harvested and assessed for weight and quantity.
Hours spent hoeing and conducting in-season cultivation or applying compost extract were quantified to estimate the cost and benefit ratios of the proposed treatment with impacts on soil health and crop yields as additional variables.
The field site was open for visitors, students and interns to gain knowledge and hands-on training on compost preparation, application, weed counts, soil sampling, and impacts of each treatment on weeds and crop yield.
The project-team (the Goods and Dr. Zinati) met in late May 2016 to discuss crop varieties (Turnip ‘Hakurei’; Lettuce ‘Jericho’; and Cabbage ‘Melissa’), establish seedlings in greenhouse and the experimental design and the treatments. Lettuce variety was changed from what was listed in the proposal. The project-team met again in early July to layout the experimental design, flag the treatments for establishing cabbage beds, and discuss the timing for compost extract applications. In late July of 2016, the project-team met to flag and prepare turnip and lettuce beds, and discuss the timing of compost extract applications.
Compost extracts were prepared 24 hr before application. They were prepared at 1:3 dilution (V:V) using deionized water. They were screened and applied using a knapsack sprayer.
Cabbage beds were prepared on July 8, 2016. Pre-planting compost extract was applied on July 11, 2016 and cabbage seedlings were transplanted on July 13. Post-planting compost extract was applied on July 14, August 3 and 24 of 2016. Cabbage seedlings were covered with row covers immediately after planting.
Turnip seeds were directly seeded while lettuce seedlings were transplanted on August 18, 2016. Compost extract was applied pre-plant one day before seeding turnip and transplanting lettuce, while post-plant extract application occurred on August 19, 2016 for turnip and lettuce and on September 16, 2016 for lettuce only.
Soil bulk density and soil compaction were assessed at end of the season per crop. The depths at which soil penetrometer readings were 300 psi were recorded and the averages of three readings per each treatment were used to determine the depths where root growth would be restricted.
Weeds were collected from random 5.4 square foot quadrats in the middle rows per treatment and assessed for diversity, biomass and density.
Turnips were harvested on September 28 and October 7 of 2016. All turnips were assessed for total weight (leaf and root) to determine root to leaf ratio, weight of total root bulbs per plot, and number of root bulbs per plot. Weight of turnip leaf was determined by difference between total weight and weight of root bulbs. Harvested root turnip was grouped into marketable and culls, where culls were either cracked or had pest injury.
Lettuce heads were harvested from all plots on October 7, 2016. Lettuce heads were cut at the crown level and counted per treatment and yield was recorded.
Cabbage heads were harvested on four occasions: October 13, 24, November 4 and 18 of 2016. Some of the cabbage heads that were not ready for harvest on November 4 were given more time to grow and fill as weather warmed up. Cabbage heads were cut at the crown level and counted per treatment and yield was recorded.
- July 15, 2016– About 182 people attended the field day and about 110 people were provided with information on the concept of using designed compost extract for soil conservation and weed control for cabbage.
- July 20, 2016– The CRAFT group of 25 participants visited the site and information on how compost extract can be considered as one tool in the tool box for no-till plant production was discussed.
- July 30, 2016– Information on the project and a demonstration of compost extract preparation were provided to a group of 55 students from Lehigh University.
- September 9, 2016– Two growers from Alabama and Pennsylvania visited the site and were provided with information regarding project objectives and the impacts of using designed compost extracts as alternative to cultivation for weed suppression.
- October 4, 2016– A group of 6 people from the Hudson Valley Farm Hub toured the experimental field site and were shown the impact of treatments.
- November 8, 2016- Dr. Zinati made a poster presentation at the American Society of Agronomy (ASA) in Phoenix, AZ. Fifteen attendees visited her poster and showed interest in the project concept and the successful results of using compost extracts for weed suppression. A tweet of this poster was seen 2,463 times and reached at least 48.3k and a press release was published on Rodale Institute’s website on the poster presentation on November 19, 2016 http://rodaleinstitute.org/rodale-institute-at-agronomy-crop-soil-science-conference/
- December 15, 2016– Information about the project was shared with two representatives from Pacific Foods and three Chinese delegates from IFOAM.
Impacts and Contributions/Outcomes
Preliminary results showed that weed biomass in turnip and cabbage beds was significantly lower in treatments that received compost extract application than in grower standard treatment or no treatment. Weed biomass in the turnip beds was 43% lower when compost extract was applied as a post-planting and 38% when applied pre and post-planting compared to no treatment while the in-season cultivation reduced weed biomass by 11% only. In lettuce beds, weed biomass was lowest (33%) only when compost extract was applied as a pre- and post-planting treatment compared to no treatment. Overall, it seemed using compost extract before planting was necessary to reduce the weed pressure.
Pennsylvania smart weed, galinsoga and wild radish were the major weeds in turnip and lettuce beds, whereas in cabbage, aster and plantain weeds were among the major weeds.
There was no significant difference in soil bulk density but in soil compaction between treatments. Mean penetrometer readings were 27.58 cm in post-planting compost application and 28.75 cm in pre- and post-planting compost application. These values were significantly different from those measured under grower’s standard treatment (20.04 cm) and no treatment (21.33 cm). These results illustrate that multiple in-season cultivation passes increase compaction after only one growing season compared to soils with no cultivation but with compost extract applications which would allow for better plant root growth and consequently better yields.
Statistical analyses of crop yields, weed diversity, and soil chemical and biological properties are underway.