Final report for GS21-253
Project Information
Electric cover crop termination holds great potential to increase sustainability of reduced-tillage systems by minimizing the need for herbicides and reducing the disturbance of the soil during traditional cover crop termination practices. There exists a critical need for recommendations for the timing and use of electric cover crop termination in reduced-tillage vegetable systems. The objectives of this project are to fill this need by developing recommendations for and evaluating the economic viability of using electric termination of cover crops in reduced-tillage vegetable systems. Three separate studies will be conducted in sweetpotato, cucumber, and a brassica crop to determine the impacts of electric termination of cover crops on crop yield and quality. Additionally, an economic analysis on the cost/benefit ratio of this technique will be conducted and compared with existing practices to determine the economic viability of electric termination of cover crops. Effective recommendations will be developed and disseminated to growers following the conclusion of these studies, in addition to the development of future research objectives based on the results of this work.
1. Develop recommendations needed for electric cover crop termination to optimize vegetable crop yield and quality.
2. Assess the cost to benefit economics for using the electric method of cover crop termination and disseminate research-based knowledge and recommendations through grower meetings, technical extension articles, and refereed journal publications.
Research
Objective 1. Three separate studies will be conducted in sweetpotato, cucumber, and a brassica crop with similar experimental methods. Each study will be a 2 x 5 x 2 factorial design with 4 replications. The three factors will be tillage (reduced-tillage or conventional tillage), cover crop type (cereal rye, clover, wheat, daikon radish, Austrian pea) and timing of electric application (once or twice). Nontreated plots will be included for comparison. Cover crop planting date is anticipated to vary depending upon the preceding crop harvest date and local weather conditions. In general, cover crop planting will occur as soon as possible after harvest and land preparation to maximize biomass production potential.
Termination of cover crops in traditional tillage plots will follow locally accepted practices with combinations of flail mowing, incorporation with scalloped disc blades, and/or moldboard plow/inversion tillage prior to finish tillage and bed/ridged row formation. In reduced-tillage plots, cover crops will be terminated in the spring with the Weed Zapper approximately three to four weeks before transplanting and again one or two weeks prior to planting or seeding the crop. Sweetpotato cuttings will be transplanted with a no-till transplanter designed to reduce cover crop residue disturbance and equipped with a modified press wheel to ensure superior soil to sweetpotato cutting contact. Pickling cucumber and the brassica crop will be seeded onto raised (cucumber) or flat (brassica) beds using a tractor mounted planter.
Cover crop biomass will be quantified by collecting above-ground portions of all plant material in a representative 1 m 2 area at the center of each plot several times between cover crop emergence and cover crop termination. Cover crop and weeds (if present) will be separated, oven-dried at 70 ℃ and weighed to record shoot dry biomass. Crop stand count, crop canopy height and length of longest vine (sweetpotato only) will be recorded. Crop vigor and canopy coverage will be assessed visually at 2, 4, 6, 8, 10, and 12 WAT (depending on crop). All crops will be harvested to determine the effect of treatment on yield and quality. For sweetpotato, storage roots will be harvested and graded into jumbo (> 8.9 cm in diam), no. 1 (> 4.4 cm but < 8.9 cm), and canner (> 2.5 cm but < 4.4 cm) and weighed, and the no. 1 class. Storage root shape and volume will be classified using an Exeter optical grader. Cucumber will be harvested 2 to 3 times per week for approximately 3 to 4 weeks and graded into oversized (> 5.1 cm diam), no. 3 (> 3.8 cm but < 5.1), no.2 (> 2.7 cm but < 3.8 cm), and no. 1 (< 2.7 cm) and then weighed. Brassica crop will be harvested as needed and weighed. Data for cover crop biomass, crop establishment and vigor, vine length, and crop yield will be subjected to ANOVA by SAS Proc GLIMMIX. Cover crop treatments and tillage methods will be treated as fixed effects whereas year, location, and replication within location will be treated as random effects. Means will be separated using Fisher’s Protected LSD (P < 0.05).
Objective 2. Data from the preceding study will be used in conjunction with the expected input costs for each system to determine the cost to benefit ratio. Inputs costs for cover crop termination methods will be compared to those of typical conventional and organic (when applicable) systems.
Initial Study Designs
Our goal in this project is to test the viability of combining roller crimpers with electricity for cover crop termination. The Weed Zapper™ (Old School Manufacturing, Sedalia, MO, USA) is a PTO-driven implement that delivers electricity to vegetation through a copper electrode. Cover crops are commonly terminated with synthetic herbicides and desiccants, which are not suitable for organic production systems. Studies were designed to evaluate the viability of electrical termination as an alternative to conventional herbicides for termination of fall-planted cover crops.
Four cover crops (rye, wheat, crimson clover, Austrian winter pea) were selected and seeded onto 42 inch beds for two trials each during fall of 2021 and 2022. Termination of cover crop species was planned for April in the following year, followed by ratings, biomass collection, and crop planting. In 2022, the cover crop did not have acceptable survival and establishment over the winter; as a result, we determined that the studies should be terminated and another attempt should be made the next fall. In 2023, the cover crop was established successfully; however, supply chain disruptions delayed the acquisition of an appropriately sized tractor for the use of the Weed Zapper until late May. By this point, many of the cover crop species had already senesced and thus the termination study was no longer possible. As a result, we made the decision to attempt similar studies using summer cover crops in order to examine the viability of our system for potential use in fall/winter-planted crops.
Pilot Study
A pilot study was conducted in the field in 2023 in order to determine the viability of electrical application as a termination method for various types of cover crop species. Four cover crops (pearl millet, cowpea, sunn hemp, sorghum-sudangrass) were planted on August 2, 2023 at the Horticultural Crops Research Station in Clinton, NC. Termination treatments consisted of weed zapper one pass and weed zapper two passes. Termination treatments were initiated on October 16, 2024. Data from the pilot study were analyzed in SAS version 9.4.
The main effect of cover crop species was highly significant (p < 0.0001) (Figure 1). The number of weed zapper passes was not significant, nor was the interaction between cover crop species and number of weed zapper passes. Pearl millet, sunn hemp, and sudangrass all resulted in higher percent kill than cowpea at one week after termination. Percent kill of pearl millet and sunn hemp were not different from one another, but pearl millet resulted in higher percent kill than both sudangrass and cowpea.
Sunn Hemp Studies
Two studies were initiated in August of 2024 in Clinton, NC to determine the effect of the Weed Zapper combined with roller crimpers on cover crop termination and biomass. Sunn hemp was selected as the cover crop due to both the results of the pilot study as well as its ability to grow rapidly. The study design consisted of a randomized complete block design with four replications. Treatments consisted of five termination methods, including: no termination, Weed Zapper one pass, Weed Zapper two passes, crimper alone, and Weed Zapper one pass followed by crimper. Sunn hemp was broadcast seeded by hand at a uniform rate of 90 kg ha-1. Treatments were applied at 6 weeks after cover crop planting. Weed Zapper treatments were applied first followed immediately by roller crimper treatments. Visual percent control ratings were collected at 1, 2, and 4 weeks after treatment (WAT). Fresh weights were collected from each plot in a 1 m2 quadrat at 10 days after treatment (DAT).
Residuals were plotted and visually examined to ensure homogeneity of variance. ANOVA was performed in SAS Version 9.4 (SAS Institute Inc, Cary, NC) using the MIXED procedure. Least squared means were separated using Tukey’s Honestly Significant Difference (α = 0.05). Treatment and run were treated as fixed effects while replication nested within run was treated as a random effect.
Percent Control
Percent control data were pooled across runs as no significant treatment by run interactions were observed. Termination method had a highly significant (p<0.0001) effect on visual sunn hemp control at 1 WAT (Figure 2) and 2 WAT (Figure 3). At 1 WAT the Weed Zapper two pass and crimper + Zapper treatments provided better control than the Weed Zapper one pass or crimper alone treatments, providing 71 and 63 percent control, respectively. The Weed Zapper one pass treatment provided better control than the crimper alone, providing 45 and 25 percent control, respectively. The same trend largely existed at 2 WAT with the exception of the crimper + Zapper treatment, which had similar control to the Zapper one pass treatment. This difference in control resulted primarily from regrowth of cover crop and recovery from the initial treatment. At 4 WAT, percent control was unchanged from 2 WAT and thus data are not presented.
Fresh Weight
Fresh weight data were pooled across runs as no significant treatment by run interactions were observed. A significant effect (p = 0.0272) was observed from termination treatment on fresh weight at 10 DAT (Figure 4). The only termination method that was significantly different from the no termination treatment was the Weed Zapper 2 pass treatment, which resulted in a fresh weight of 10730 kg ha-1. Fresh weights of other treatments included 15620 kg ha-1 from the no termination, 12080 kg ha-1 from the crimper alone, 11980 kg ha-1 from the Weed Zapper 1 pass, and 11610 kg ha-1 from the crimper + Zapper.
Discussion
All termination treatments provided better visual control of sunn hemp than did the crimper alone. By 2 WAT, the 2 pass Weed Zapper treatment provided the best visual control of sunn hemp, resulting in an average of 67 percent control. By contrast, the next best treatments provided 46 and 43 percent control at 2 WAT. The 2 pass Weed Zapper treatment provided 24 percent better control than the 1 pass treatment, indicating that an increased number of applications may be necessary to increase termination efficacy in sunn hemp. Though the 2 pass Weed Zapper treatment was the only treatment that differed significantly in fresh weight at 10 DAT compared to the no termination treatment, the overall numerical trend was the same as in the percent control at 2 WAT.
The results of these studies indicate that the Weed Zapper is potentially useful for sunn hemp and other cover crop termination. Percent control results show that the Weed Zapper treatments performed better than the crimper alone, and that the two pass treatment provided the best control of all termination methods tested. Fresh weight results show that the 2 pass Zapper treatment is the only treatment that significantly differed from the no termination treatment. At 2 WAT the crimper + Zapper treatment performed similarly to the 1 pass Zapper treatment, indicating that the incorporation of a roller crimper with electrical termination methods may not result in improved control over the Weed Zapper alone. Future research should evaluate the effect of the Weed Zapper for termination of other cover crop species as well determine the optimal number of passes for termination efficacy and cost effectiveness.
Educational & Outreach Activities
Participation Summary:
No outreach description available.
Project Outcomes
Using electricity is another tool for growers to sustainably terminate their cover crops without the use of a herbicide. This tool can be used in organic and conventional production systems.
No information available.
We would like to continue to evaluate use of the Weed Zapper for weed control and cover crop termination as part of a weed management and production system in vegetable crops.