Final report for GNC21-326
Project Information
Carrot is an economically important crop in Michigan with limited control options for escaped and late-emerging weeds. Powell amaranth and horseweed are the most troublesome weeds, which escape from early management practices and cause significant issues at carrot harvest and reduce yield. Electrical weeding eliminates weeds that are taller in height than the crop canopy and has the potential to reduce the amount of between-row cultivation, herbicide application, and hand labor needed to achieve weed control. Upon contact with the applicator electrode, electric current is conducted through the weed and dissipated from the roots into the surrounding soil. The key advantages of electrical weeding are that it is chemical free, systemically kills the plant roots, and does not disturb the soil. While electrical weed control is gaining momentum as a promising new weed control method, fundamental knowledge of the technology’s impact on weed control, crop safety, and soil health are lacking. At present, it is unknown what consequences this influx of energy has on soil microbes. Therefore, field studies will be conducted in carrot to evaluate the effect of electrical weeding on weed control, crop safety, and soil microbial communities. These results will shed more light on potential damage to or stimulation of soil microbes/nutrients caused by electrical weeding and enhance the knowledge around the use of electricity-based weed control in carrot production systems. Greater knowledge of agroecosystem energetics and interactions at the plant/soil level will enable the electrical weed control industry to advance their technology to better serve the needs of producers. These results will be shared with growers through professional meetings, on-farm field days, and extension publications.
Learning outcomes for the vegetable grower community will include:
- Greater familiarity with how the electrical weeding works and its potential in an integrated weed management (IWM) plan for weed control in carrot
- Impact of the electrical weeder on carrot crop yield and quality
- Enhanced insight into how electrical weeding influences soil microbes.
As electrical weeding finds greater use in both conventional and organic systems, vegetable growers will for the first time have empirical data into its impact on soil food web functioning with which they can use to refine their weed control strategies. The expected learning outcomes should mature into the following action outcomes:
- The results from this study will be beneficial for carrot growers and help them to improve the profitability and sustainability of their weed management programs.
- Growers may choose to adjust management plans in light of trends in data that reveal soil biology effects from electrical weeding
- Manufacturers and farmers alike will be spurred towards further innovation to reduce any off-target damage while retaining the benefits.
- Farmers will be empowered to take action to improve their soil biology through informed management practices, whether pertaining to electrical weeding or as a more holistic, whole-farm approach.
Cooperators
- (Researcher)
- (Researcher)
Research
Field trials were carried out in Hart, MI during the summer of 2021 and 2022. Separate carrot trials were conducted in each field season (cultivar Canberra in 2021 and Belgrado in 2022). The experiment was structured as a spit-plot design with four replications. The main plot factor was late-season weed control methods and included: 1) one hand-weeding event (HW), 2) one electrical weeder pass (1P), 3) two electrical weeder passes performed consecutively [2P(ST)], 4) one pass followed by one pass after a 14-day interval [2P(14d)], 5) two passes followed by one pass after a 14-day interval (3P), and 6) no late-season control (NLC). Within each main-plot variable, the sub-plot factor tested different early-season weed control methods in order to produce different weed densities with which to test the late-season weed control methods. These consisted of 1) one application of postemergent herbicide linuron (Lorox; Tessenderlo Kerley, Inc., Phoenix, AZ; “Low” early-season control; ), 2) two applications of linuron (“Medium” early-season control), 3) two applications of linuron and one application of the preemergent herbicide pendimethalin (Prowl H2O; BASF Ag Products, Ludwigshafen, Germany; “Intensive” early-season control), 4) a weed-free control and 5) no early-season control (NEC). Each sub-plot early-season weed control treatment was tested on individual 1.8-m by 10.7-m beds, comprising five beds per main plot with three carrot rows per bed. Each sub-plot was further divided into two sections: a front section to use for collecting in-field data such as weed control ratings, weed counts, and crop yield at harvest, and a back section from which soil and seed samples were collected without compromising in-field data through sampling disturbance.
Initial applications of pendimethalin were performed in early May using a CO2 pressurized backpack sprayer at a rate of 2.13 kg ai ha-1 in 2021 and 1.06 kg ai ha-1 in 2022. The first application of linuron was performed 3-4 weeks after the preemergent at a rate of 1.12 kg ai ha-1. The final linuron application was applied 3 weeks afterwards at 1.12 kg ai ha-1. Weed counts and timed hand weeding treatments were performed four to six weeks after the final herbicide application. The first electrical weeding treatment took place one week after weed counts in 2021 and three weeks after weed counts in 2022. Environmental parameters such as percent cloud cover, relative humidity and soil moisture/temperature were recorded at the time of application for every treatment in both trials during the 2022 season.
The electrical weeding equipment used for the trials was the Annihilator 12R30 manufactured by the Weed Zapper™ (Old School Manufacturing LLC, Sedalia, MO) and owned/operated by the growers at Oomen Farms. An operating speed of 1.6 to 3.2 km/h at 230 horsepower was maintained for all treatments in both trials. Electrical treatment was timed for when a substantial proportion of the weeds were at least 10.2 to 15.2 cm taller than the crop, per manufacturer recommendations (Old School Manufacturing LLC 2020). In both carrot trials, redroot pigweed had formed mature seedheads, with seeds close to a dark brown color, by the time electrical weeding was performed.
Root zone soil samples were collected from the carrot trial for both years. Samples were taken at a depth of ~7.6 inches from the root zone of electrocuted weeds within each treatment immediately following EW#1 and #2. Bulk soil samples from the NLC plots were pulled at random areas from the sampling section due to lack of treated weeds. The soil samples were sieved to a particle size of 2 mm and stored at 4 C prior to analysis.
Within 4 weeks of sampling for both the EW#1 and #2 samples, 10 g (± .02g) subsamples of field moist soil were weighed to attain fresh weight (mw) before being dried at 100 C. After at least three days, the subsamples were re-weighed to attain the dry weight (md) and gravimetric soil moisture content (θ).
Changes in microbial biomass were measured using the chloroform fumigation extraction method outlined in Vance et al. (1987). To determine the amount of C contained within microbial biomass, 8 g soil sub-samples were fumigated by adding 2 mL CHCl3 (chloroform) stabilized with non-polar hydrocarbons and left to incubate for 24 hours. Another unfumigated 8g sub-sample underwent C extraction by addition of 40 mL of 0.5M K2SO4 and agitation using an orbital shaker at 200 RPM for 1 hour. The extracts were filtered out and stored at -20 C until analysis. Following incubation, the fumigated samples were vented for 2 hours and extracted/stored using the same protocol. Extract sub-samples were analyzed for total organic carbon (TOC) and total nitrogen (TN) using a Shimadzu TOC-V analyzer (Shimadzu Scientific Instruments, Kyoto, Japan).
Short-term changes in root zone inorganic N concentrations were measured using an inorganic N extraction procedure adapted from Mulvaney (1996). A volume of 50 mL 1M KCl was added to flasks containing 10 g soil before being agitated on orbital shaker at 200 RPM for 30 minutes. The extracts were then filtered out and stored at -20 C prior to analysis. Samples were analyzed for ammonium (NH4+) and nitrate (NO3-) using a Lachat 8500 Quikchem flow injection analyzer (Hach Company, Loveland, CO).
All data was subjected to ANOVA using SAS 9.4 (SAS 9.4, SAS Institute Inc., Cary, NC) PROC GLIMMIX and means separation using Fisher’s Protected LSD (P ≤0.05). All data was checked for normality and homogeneity of variance before statistical analysis by plotting residuals. Data was analyzed by year for carrot due to the variability in the data collection timings. Late-season weed control practices, early-season control practices, and their interaction were considered fixed effects and replication as a random effect.
Mulvaney RL (1996) Nitrogen—inorganic forms. Methods of soil analysis: Part 3 Chemical methods 5:1123-1184
Vance ED, Brookes PC, Jenkinson DS (1987) An extraction method for measuring soil microbial biomass C. Soil biology and Biochemistry 19:703-707
In the conventional carrot trial, there were fewer below-canopy weeds compared with another trial conducted in organic green beans, due to stronger early-season control from herbicide usage. This led to the same weeds being electrocuted at both electrical weeding timings, showing limited utility of including a 14-day interval. This finding indicates that number of passes and their timing can be adapted based on the relative height and density of weeds to optimize control while minimizing unnecessary passes over the field. Evidence from the carrot trial supports the assertion that electrical weeding has lower performance in higher weed densities.
Electrical weeding can lead to higher in-season crop injury than hand weeding but was not found to cause any internal damage to carrot root tissue. Crop injury was higher in the organic green bean system compared to this carrot trial, due to greater number of weeds growing at- or below-canopy, which required more aggressive electrical treatment in order to get sufficient control which resulted in more electrode contact time with the crop foliage. There was no significant increase in carrot yield from electrical weeding in either year. Hand weeding only appeared to be correlated with a yield increase in 2022. This indicates that primary advantage of electrical weeding as a form of late-season control is not to increase yield in the current crop, but to control escaped weeds before they develop or disperse seed in order to decrease weed pressure in later years.
There is little to no evidence that electrical weeding is having any negative effect on rhizosphere microbial populations by looking at microbial biomass C and N, as well as when looking at inorganic N as an indicator of N cycling dynamics. Increased MBC for 1P over the non-treated in 2021 may suggest that the impact of electricity can increase population size through greater organic sources released into the rhizosphere upon plant death or hormetic stimulation of microbial communities. Further research looking at delayed changes in root zone MBC/MBN and inorganic N over time, as well as expanding to investigate changes in functional diversity in the rhizosphere, could be useful in developing a more in-depth picture of electrical weeding’s impact on soil microbial communities.
In comparison with conventional systems where electrical weeding is not used, there does not seem to be a yield difference despite the increased late-season weed control and crop injury. As well, there does not seem to be a negative impact on soil microbial communities from including electrical weeding.
Educational & Outreach Activities
Participation Summary:
New educational materials developed include hand-outs summarizing major points of the research at the 2021 and 2022 Oceana County Vegetable Research Tour, as well as unique hand-outs distributed at the 2021 and 2022 Great Lakes Expo. An on-farm demonstration of the electrical weeding equipment also took place during the 2021 Oceana County Vegetable Research Tour and the 2022 Midwest Mechanical Cultivation Field Day.
An article on the research was published in the trade magazine Carrot Country. Presentations at the 2021 and 2022 Great Lakes Expo and the 2021 Michigan Carrot Committee meeting were given. Electrical weed control field days were carried out in 2021 and 2022 as part of the Oceana County Vegetable Research Tour. An extension video "Introduction to Electrical Weed Control" was created and made available for growers on Youtube.
In-progress projects include: 1) a journal article for publication in Weed Technology, and 2) a Michigan State University Extension article.
Project Outcomes
Electrical weeding is a new technology that shows promise as an environmentally benign method of controlling escaped or herbicide-resistant weeds. Greater adoption and refinement of this equipment can contribute greatly to the sustainability of agricultural systems by increasing production while limiting use of herbicides. The research targets key areas that needed to be addressed to evaluate the efficacy of this tool, as well as its potential for causing damage to the crop and associated soil microbial communities. The outcomes of the experiments have special implications for future sustainability, as the information created by the research is shared and built upon in the years to come.
Electrical weed control's viability as a late-season management tool depends on it having acceptable levels of performance and off-target damage. The research determined factors impacting weed control efficacy and crop injury in carrot production systems (weed-crop height differential and weed density, primarily) and observed little damage to population size and N cycling dynamics in rhizosphere soil microbial communities from the electrical current. This provide valuable information regarding the environmental and economic considerations underlying the decision to purchase or use this new equipment. As well, the results help to legitimize the tool for both organic and conventional growers as a new addition to their integrated weed management plans.
Over the course of the project, my advisor and I gained valuable knowledge regarding the operational and environmental variables that impact the efficacy of electrical weed control. This knowledge was gained through background research, conversation with growers, and through observation when conducting the research trials. Insight into the utility of electrical weeding in a farm's integrated weed management plan, with reference to both the positive and negative aspects of adopting this equipment, was gained through the experimental work. Key skills such as conducting field research, sharing results through extension outreach (events, publications, video), and analyzing data to create new knowledge were also developed and strengthened through this project. The awareness of electrical weeding's potential as a non-chemical form of late season weed control and its impact on soil microbial communities will inform the understanding of my advisor and I through the remainder of our careers, guiding extension recommendations and ideas for further research.
Future studies can investigate the response of different weed species to electrical treatment, use of the equipment for control of bolting carrots, and the potential of the equipment as an organic form of cover crop termination.
We would like to thank SARE for helping to make this research possible and for their work in helping to empower growers to adopt sustainable agriculture practices for improved environmental, economic, and social outcomes.