Final report for GNC21-324
Project Information
Title: Addressing Weed and Soil Management Trade-offs in Vegetables Through Integrated Cultural and Mechanical Strategies
Context: Weed management is a major challenge for vegetable growers. Over-reliance on hand-weeding, herbicides and tillage to manage weeds has contributed to both economic and environmental challenges including herbicide pollution, soil degradation and development of herbicide resistance. By integrating cultural and advanced mechanical weed management strategies, we hypothesized that Midwest vegetable growers could more effectively control weeds while minimizing environmental costs. We also hypothesized that better understanding of the interactions between soil management and mechanical cultivation tools would help growers find an optimal balance between weed and soil management objectives.
Project Objectives: This project had 3 central objectives: 1) Evaluate the benefits of integration of cultural and mechanical weed control in carrots using seed-sizing and in-row mechanical cultivation tools; 2) Explore how soil management practices including historic tillage, compost addition and bed preparation influence the efficacy of mechanical cultivation in winter squash and 3) Coordinate with growers to test and share best practices.
Approach. We took advantage of a long-term cropping systems experiment to evaluate interactions between soil management practices (tillage, compost and bed-preparation) and in-row mechanical cultivation efficacy in acorn squash. We also conducted field studies to evaluate strategies for integrating cultural and mechanical weed control in carrots, including the effects of seed quality on the efficacy of mechanical cultivation. We used a novel 3D Lidar imaging approach to visualize and analyze soil conditions and their interaction with tools. Our findings were shared with growers through conference presentations, field days and posting on the Physical Weed Control forum website.
Key conclusions. Findings from experiments in carrots (objective 1) reinforced our observations from cultivation testing in other vegetables that at early growth stages hilling is often more efficacious and less damaging to crops than ‘scrubbing’ using a finger weeder. This observation is consistent with our greenhouse evaluations which confirmed that carrots often have a greater height advantage compared to anchorage force advantage relative to weeds (especially grasses) at early growth stages. Hilling also has the advantage that it is easier to accomplish with precision. However, it should be noted that these results may not hold for other crops or later growth stages in carrots. We also observe improved early vigor and a 20% yield advantage of carrots from the largest seed fraction compared to the smallest seed fraction from a single seed lot. Future studies confirming this result across other cultivars and seedlots may provide a simple strategy for improving profitability of carrot production.
Results related to Objective 2 demonstrate the potential impact of soil conditions and cultural practices on cultivation tool efficacy. Historic compost additions improved selectivity of mechanical weed control with either finger weeders or hilling disks at the 2-leaf squash growth stage. We speculate that improved selectivity in compost-treated plots was due at least in part to more vigorous early squash growth, which conferred greater tolerance to physical disturbance. Hypothesized effects of historic soil management on soil surface conditions impacting cultivation tool efficacy were not consistently detected in this study. Nonetheless, we believe that our approach of using 3-D surface imagery to characterize surface topography is a valuable method for evaluating the impact of previous soil management on cultivation efficacy, as well as the impact of cultivation tools on soils.
Project Outcomes: Knowledge gained from this research was shared with growers at conferences and field days. We believe that growers attending these events gained knowledge to help them integrate cultural and mechanical weed management strategies to reduce the economic and environmental costs of weed management on their farms. Growers have obtained greater understanding of the interaction between cultivation tools and soil conditions to help them optimize their soil and weed management choices for their specific conditions to successfully manage weeds without excessive tillage.
This project had 3 central objectives:
1) Evaluate the benefits of integration of cultural and mechanical weed control in carrots using seed-sizing and in-row mechanical cultivation tools
2) Explore how soil management practices including historic tillage, compost addition and bed preparation influence the efficacy of mechanical cultivation in winter squash
3) Coordinate with growers to test and share best practices.
Cooperators
Research
This project took place during the 2022 growing season when Objectives 1 and 2 were addressed through field trials at the Michigan State University Horticulture Teaching, Research, and Education Center (HTRC) on certified organic land with a Spinks loamy sand soil characteristic of many vegetable soils in the region.
Objective 1: Integrating Cultural and Mechanical Weed control in Carrots.
Field Experiment. Factors for this experiment included carrot seed size (small vs large) and cultivation tool type (finger weeder vs hilling disk vs handweeded control). Different seed size classes from a single seed lot of cultivar 'Bolero' were obtained using a seed blower to separate the top and bottom quartiles of seeds. All 6 combinations of the two experimental factors were evaluated in a split-plot design with tool as the main plot factor, and seed size as the subplot factor. Main plots measured 5’ x 60’ and included a single bed of carrots with 3 rows spaced at 15”. Pre-plant tillage included chisel plowing, field cultivation (Perfecta), and shallow rototilling to create a uniform, level bed prior to planting. After weed emergence, but before carrot emergence, all beds were flame weeded to kill the initial flush of weeds. Between- and near-row cultivation was accomplished with a basket weeder, leaving a narrow 2-3” band of undisturbed soil in row for subsequent in-row tool testing. A single in-row handweeding and thinning event occurred 16 days after planting (DAS). In-row cultivation tool treatments occurred at 22 DAT (carrots at 1-2 leaf stage) and again at 45 DAT (4-5 leaf carrots). Weeds evaluated included ambient weeds emerging following the initial handweeding and/or surrogate weeds (condiment mustard or red amaranth) sown approximately 1 week prior to tool testing. In-row cultivation used either finger weeders (Tilmor) or hilling disks (Kult Kress ‘Duo’ cutaway disks set to hill) belly-mounted to a manually-steered Tilmor cultivating tractor. Fingers were calibrated with the goal of killing weed primarily by ‘scrubbing’ soil from the in-row zone to uproot weeds, rather than pushing soil into the row to bury them. This involved raising the toolbar and adjusting the toobar angle such that the floating arm sloped downward slightly (approximately 10-15o from horizontal) until soil was observed moving out of the crop row in the calibration area. Tips of fingers were set to leave a 1 cm minimum gap between tips of the fingers, centered on the crop row. Data collection occurred before and after each cultivation event. Counts of emerging carrots and weeds were recorded in two 1.25 x 0.10 m permanent quadrants in each plot to evaluate tool efficacy and selectivity. Carrot and weed height and anchorage forces were evaluated at 3-4 day intervals up to the time of the second cultivation. Carrots were harvested and evaluated for quality based on size, forks, nubs and splits. The effects of cultivar, seed size and tool and their interactions on all responses were evaluated using ANOVA in R statistical software.
Greenhouse studies. To gain perspective on the optimal choice of tools for controlling weeds in carrots at early growth stages, we grew carrots, three weed species (common lambsquarters, large crabgrass and giant foxtail) and two surrogate weeds (red amaranth and condiment mustard) in pots in a greenhouse and measured their heights and anchorage force at 2-3 day intervals. The height and anchorage force of carrots relative to weeds provides insight into whether hilling or uprooting strategies are more likely to be effective at different growth stages.
Objective 2. Explore how soil management practices affect efficacy of mechanical cultivation in winter squash.
Experimental treatments and design: This experiment was embedded in a long-term (12 year) cropping systems trial evaluating tillage and compost effects on soil and weed management in a 4 year sweet corn-snap bean-broccoli-squash rotation. Factors for this experiment included two levels of historic tillage (conventional vs. reduced tillage), two levels of historic compost addition (3 dry tons/a/yr vs none) and two cultivation tool sequences (hill-finger vs finger-finger).
Pre-plant soil management. Pre-plant tillage and compost applications followed the protocols from our long-term trial that had been in place in the same plots since 2009. The entire experimental area was planted with a rye-vetch cover crop mixture the fall prior to squash production. Conventionally tilled main plots were chisel plowed and field cultivated in late April, and shallow-rototilled in late May. In reduced tillage treatments, the same cover crops were allowed to grow until early May, then mowed and tarped with 6 mil black plastic for 2-3 weeks to kill the cover crop and any winter annual weeds without tillage; after tarp removal in early June, plots were strip-tilled using a Hiniker 6000 unit equipped with row cleaners, offset disks and rolling basket to create 10” wide by 10” deep tilled zones at 30” spacing. Squash was transplanted by hand on 16 June.
Cultivation events. In-row cultivation events occurred on 21 June and 30 June. Weed and crop counts were conducted in permanent quadrats before and after each cultivation event to determine weed and crop mortality. Prior to each cultivation event, soil surface characteristics were evaluated including penetrometer resistance, moisture content and topography. LIDAR 3D point clouds were used to estimate surface roughness as well as the extent of soil shattering following cultivation events. Squash was harvested and data on yield, quality and final weed biomass collected on 23 September. The effects of soil treatments on the efficacy and selectivity of finger weeding and hilling were evaluated using ANOVA in R. In addition, the relationship between soil surface characteristics and tool efficacy was evaluated using multivariate regression.
Objective 3: Grower Collaboration and Outreach
We shared our results with grower collaborators through presentations at grower-meetings including the Great Lakes Fruit, Vegetable, and Farmer’s Market Expo (GLEXPO; Root Crop Session and Large Scale Organic Session) and the Midwest Mechanical Weed Control Field Day in Benton Harbor MI in September 2022. Results were also shared in field demonstrations at the Weed Day (MSU Horticulture Teaching and Research Center, Holt, MI), and the Midwest Mechanical Weed Control Field Day (MSU SWMREC Research Station, Benton Harbor, MI) and through postings on the Physical Weed Control Forum.
Objective 1: Integrating Cultural and Mechanical weed control in Carrots.
Key Results. We found that carrot seedlings from large seeds had 20% greater anchorage force and 12% greater height than those from smaller seeds at time of early cultivation. Although we hypothesized that these differences would facilitate greater tolerance to mechanical cultivation, no significant impact of seed size on carrot mortality due to cultivation was detected. At the 1-2 leaf carrot growth stage, selective in-row cultivation was challenging regardless of tool or seed size: carrot mortality at this stage ranged from 10-33%, with weed mortality ranging from 30-72% for red amaranth, and 21-60% for mustard. In contrast, at the 4-5 leaf carrot growth stage in-row cultivation did not impact carrot survival, and resulted in 85-90% mortality of red amaranth, and 70-84% mortality of mustard. Carrot yield and quality were reduced where aggressive early finger weeding occurred. However, hilling did not result in reductions in carrot yield. Interestingly, carrots from the large seed fraction had 20% greater yield than those from the small seed fraction, regardless of mechanical cultivation treatment. These results reinforce our observations from cultivation testing in other vegetables, that at early growth stages hilling is often more efficacious and less damaging to crops than ‘scrubbing’ using a finger weeder. This observation is consistent with our greenhouse measurements which confirmed that carrots often have a greater height advantage compared to anchorage force advantage relative to weeds (especially grasses) at early growth stages. Hilling also has the advantage that it is easier to accomplish with precision. However, it should be noted that these results may not hold for other crops or later growth stages in carrots. Although our results did not confirm the value of carrot seed quality for improving tolerance to cultivation, we did observe improved early vigor and a 20% yield advantage of carrots from the largest seed fraction compared to the smallest of a single seed lot. Future studies confirming this result across other cultivars and seedlots may provide a simple strategy for improving profitability of carrot production.
Objective 2. Explore how soil management practices affect efficacy of mechanical cultivation in winter squash.
Contrary to expectations, long-term reduced tillage (strip tillage and/or tarping) had little to no detected impacts on soil surface characteristics (penetrometer resistance; moisture; or surface roughness) in the crop row, nor did it influence the efficacy of mechanical cultivation in squash. In contrast, depending on the year and timing, historic compost addition impacted soil surface characteristics and the efficacy of mechanical cultivation. At the 2-leaf squash stage, compost addition improved cultivation efficacy in one of two years (2021) and reduced crop mortality in the other (2022). At the 4-leaf squash stage compost addition reduced soil surface penetrometer resistance and increased soil water content in 1 of 2 years (2021) but had no detectable effect on cultivation tool efficacy in either year. Compost addition increased early shoot biomass of squash in both years, and crop yield in one of two years.
Although results from this trial were variable and inconsistent across the two years, they demonstrate the potential impact of soil conditions and cultural practices on cultivation tool efficacy. Historic compost additions improved selectivity of mechanical weed control with either finger weeders or hilling disks at the 2-leaf squash growth stage. While the mechanisms responsible for this effect are not clear, we speculate that it was due at least in part to more vigorous early squash growth, which conferred greater tolerance to physical disturbance. Hypothesized effects of compost on soil surface conditions impacting cultivation tool efficacy were not consistently detected in this study. This may have been due either to 1) high variability in soil characteristic responses and insufficient statistical power to detect changes in those responses; or 2) relatively small effects of compost on those characteristics. We believe that our approach of using 3-D surface imagery to characterize surface topography is a potentially valuable method for evaluating the impact of previous soil management on cultivation efficacy, as well as the impact of cultivation tools on soils. These images are also valuable for understanding variability in mechanical tool modes of action and identifying sources of variation in results.
Educational & Outreach Activities
Participation Summary:
We shared our results with grower collaborators and educators through presentations at grower-meetings including the Great Lakes Fruit, Vegetable, and Farmer’s Market Expo (GLEXPO; Root Crop Session and Large Scale Organic Session) and Indiana Small Farms Conference. Results were also shared through field days and workshops including MSU's Weed Day (HTRC, Holt, MI, June 2021 and 22), and the Midwest Mechanical Weed Control Field Day (Benton Harbor MI, September 2022). Results were also shared at academic conferences (WSSA and ASHS) and through postings on the Physical Weed Control Forum website.
Project Outcomes
Learning Outcomes:
- Vegetable farmers have a greater understanding of the value of cultural weed management strategies including cultivar choice and use of high-quality seeds.
- Vegetable farmers are more aware of the impacts of pre-plant soil management practices on mechanical cultivation efficacy and selectivity.
- Vegetable farmers have increased knowledge of optimal choice of mechanical cultivation tools for early weed management in carrots and squash.
Anticipated future Action Outcomes:
- Vegetable farmers will integrate cultural practices into their weed management plan to reduce reliance on herbicides and limit soil degradation on their farms.
- Vegetable farmers will utilize optimal bed preparation practices and pre-planting decisions that improve cultivation efficacy without compromising soil health.
- Farmers will optimize mechanical tool choice under different soil conditions. This will allow them to more effectively use long-term management strategies that are beneficial to soil health, since they will know how to effectively choose mechanical tools to manage weeds in these varied conditions.
This project resulted in increased understanding of the challenges and opportunities for successful integration of physical and cultural weed control in vegetable production systems. Mechanical cultivation tools represent an opportunity for vegetable growers to reduce reliance on hand-weeding and herbicides. However, successful use of mechanical cultivation in sensitive crops like carrots requires careful consideration of both the timing and type of tool, and attention to cultural practices that give the crop a size advantage relative to weeds. Through our work, we identified carrot seed quality and early vertical growth as key characteristics for successful carrot cultivation. Our work also explored the potential importance of historic soil management and soil surface characteristics on tool efficacy in squash. Results point to the importance of organic matter additions for both improving crop tolerance to tools and improving tool efficacy on small weeds using various tools.
This research suggests several avenues for future studies to continue to improve the efficacy of mechanical weed control and to help farmers manage soil-weed tradeoffs while increasing profitability on their farms.
Our work in carrots (Objective 1) suggest that carrot seed quality is a major driver of early crop establishment and crop yield. Our results demonstrate the large impact of seed size (from a single commercial seed lot) on carrot vigor (height, anchorage force and biomass) at early growth stages and on final carrot yield. Preliminary screening of multiple commercial carrot varieties suggest that this result is not unique to ‘Bolero’ and warrants further study as a potentially low-cost approach to improving sustainability of carrot production systems. Our carrot studies also suggests that hilling at early growth stages has greater potential for selective management of most weeds (especially grasses) compared to ‘scrubbing’(~uprooting) and that future efforts focusing on improved precision of hilling tools in combination with cultural practices aimed at maximizing early height advantage of carrots relative to weeds would be more fruitful than those focusing on uprooting tools and root anchorage force.
Our results in squash systems (Objective 2) demonstrate 1) greater potential relative to carrots for successful selective mechanical cultivation at early growth stages using a variety of cultivation tools; and 2) the potential importance of interactive impacts of soil management on soil surface conditions impacting physical weed control. Although our results were inconsistent across years, compost addition improved the selectivity of mechanical cultivation in several cases. Future research exploring the economic tradeoffs associated with compost addition on soil health, early crop and weed growth, and the efficacy of mechanical cultivation are needed to help guide grower decisions. We believe that our approach of using 3-D surface imagery to characterize surface topography is a potentially valuable method for understanding mechanisms responsible for soil management impacts on mechanical cultivation efficacy, as well as the impact of cultivation tools on soils. Future studies focused on improving methodologies associated with analyzing and interpreting point-cloud data from 3-D images of soil surface topography and its relation to weed mortality would be valuable for efficiently understanding the mechanisms of tool action and developing strategies to improve their efficacy.