Understanding production and conservation tradeoffs of vertical tillage practices

Final report for GNE21-263

Project Type: Graduate Student
Funds awarded in 2021: $14,124.00
Projected End Date: 07/31/2023
Grant Recipient: Penn State University
Region: Northeast
State: Pennsylvania
Graduate Student:
Faculty Advisor:
Dr. John Wallace
Penn State University
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Project Information

Summary:
  1. Within the last four decades, widespread transition to no-till corn (Zea mays L.) and soybean (Glycine max L. Merr.) production in Pennsylvania have improved soil conservation and soil quality but can result in residue and pest management challenges. To effectively manage residue in no-till cropping systems, some growers have adopted vertical tillage, a residue management practice characterized by cutting and incorporating crop residue within the top 5-10 cm of soil. Despite few studies documenting effects on crop production and soil conservation, vertical tillage has become widespread.
  2. Replicated on-farm trials were conducted over a two-year period in 2021-2022 to improve grower and consultant decision-making regarding the role of vertical tillage relative to continuous no-till on southeast Pennsylvania farms located within the environmentally sensitive Chesapeake Bay Watershed. We assessed the effects of vertical tillage on corn residue cover, winter annual weed abundance, slug damage, soybean performance, pH and nutrient stratification, as well as biological and physical indicators of soil health in 40 paired strip trials comparing spring vertical tillage to no-till using three different vertical tillage tools used by farmer cooperators.
  3. Vertical tillage equipment type was a driver of variation in changes to surface residue cover. Baseline surface residue cover was similar among no-till strips, but a greater proportion (32%) of strips had mean surface residue cover levels below a 60% conservation program compliance threshold when a Kuhn-Krause Excelerator was used. Relative to no-till, vertical tillage resulted in a 50% reduction in winter annual weed cover, a 24% reduction in slug damage, and no significant differences in soybean stand establishment or grain yield.  Results from this study also indicated that vertical tillage may alleviate soil pH stratification but may not be aggressive enough to alleviate phosphorus or soil organic matter stratification as was hypothesized. Further, vertical tillage did not reduce no-till stratification of active C (POXC) or microbial respiration (CO2-burst). Additionally, long-term vertical tillage may alleviate surface crusting but may also create a compacted layer at a shallow depth relative to compaction found in soils under long-term no-till management.
  4. The primary objective of this thesis research was to provide sound scientific data from on-farm trials to improve grower and policy maker decision-making related to whether vertical tillage has a role in conservation agriculture on southeast Pennsylvania farms, which are located within the environmentally sensitive Chesapeake Bay Watershed. Questions remain regarding the tradeoffs associated with re-introducing a form of minimum tillage into an otherwise no-till system for the purposes of seedbed preparation, manure or fertilizer incorporation, compaction alleviation, or improvement of soil health, and these questions merit further investigation as producers and researchers seek a crop production model that is profitable and conservation-minded.
Project Objectives:

On-farm strip trials will be utilized to contrast no tillage with vertical tillage conducted once in the spring to manage corn residue after no-till corn grain production in transition to no-till, full-season soybean production.  Our overall objective is to characterize and communicate production and conservation tradeoffs associated with vertical tillage practices using a multi-criteria assessment.  Specific objectives include:

Objective 1. Evaluate vertical tillage effects on surface residue cover [i.e., soil erosion potential].

Hypothesis 1. We expect to measure greater than 60% surface residue cover in the no-till treatments and less than 60% surface residue cover in the vertical tillage treatments.

Objective 2. Evaluate vertical tillage effects on weed management outcomes by measuring (a) pre-plant winter annual weed control, (b) summer annual weed emergence timing [i.e., false-seedbed potential], and (c) soil-applied residual herbicide efficacy.

Hypotheses 2. Relative to no-tillage, vertical tillage will (a) reduce density of established winter annual weed species, (b) increase recruitment of early-emerging summer annual weed species due to stimulation of disturbance-related germination cues, and (c) increase soil-applied residual herbicide efficacy due to reduced herbicide interception and adsorption by crop residues.  We anticipate the magnitude of vertical tillage effects on weed control will vary considerably across locations but be partially explained by the difference in surface residue incorporation within each location.

Objective 3. Evaluate vertical tillage effects on crop performance metrics, including (a) crop emergence, and (b) crop yield.

Hypotheses 3. Relative to no-tillage, vertical tillage treatments will result in (a) more uniform soybean plant emergence and early season vigor and (b) higher crop yields.

Objective 4. Evaluate vertical tillage effects on selective nutrient management factors, including (a) pH stratification, and (b) P stratification [i.e., nutrient loss potential] across the soil profile [0-5 cm, 5-10 cm, 10-15 cm, and 15-20 cm depths].

Hypotheses 4. Relative to no-tillage, soil within vertical tillage treatments will be characterized by (a) higher pH and (b) lower soil test P levels at shallower soil depths.

Objective 5. Evaluate vertical tillage effects on short-term soil health indicators, including (a) soil organic C stratification, (b) soil penetration resistance [i.e., compaction alleviation], and (c) soil bulk density.

Hypotheses 5. Relative to no-tillage, vertical tillage will result in (a) decreased soil organic C stratification due to greater soil mixing with crop residue; (b) higher soil penetration resistance below the operating depth of the vertical tillage tools, and (c) lower soil bulk density at shallower soil depths.

Introduction:

The purpose of this project was to assess the effects of vertical tillage on crop production and soil conservation goals in long-term, no-till cropping systems within southeastern Pennsylvania. Adoption of vertical tillage has been increasing in the Northeast to address residue management and planting challenges in long-term, no-till cropping systems, yet little was known about the impact of this practice on soil conservation, soil health, pest management and crop productivity. Consequently, our proposed research contributed to sustainability goals of no-till grain crop systems in the Northeast by providing a science-based, decision-making framework for farmers to assess the impact of vertical tillage on soil conservation, water quality, crop productivity, and net farm income.  We proposed to study vertical tillage impacts on these sustainability goals with use of coordinated on-farm trials, which facilitated co-learning opportunities among growers, extension personnel, agronomic consultants, and ag retailers within Pennsylvania.

No-till crop production aims to minimize soil disturbance while maintaining at least 60% surface residue cover (Residue and Tillage Management, 2016).  This conservation practice, coupled with high corn yields, can result in accumulation of substantial crop residue on the soil surface.  A need to effectively manage previous crop residue prior to planting a subsequent crop has led to the adoption of minimum (or ‘vertical’) tillage.  Vertical tillage is primarily a residue management practice characterized by cutting, sizing and incorporation of crop residue within the top 5-10 cm of soil. 

Grower adoption of vertical tillage has steadily increased in the last 10 years, especially in southeastern Pennsylvania where increasing corn grain yields result in corresponding increases in corn residue (Adler et al., 2015).  Vertical tillage can improve crop stand establishment without having to significantly alter planting equipment to negotiate crop residues, thus off-setting planter upgrade and maintenance costs.  Performing vertical tillage also negates the need for additional replacement or after-market modification of existing harvesting equipment designed to size and distribute residue more efficiently.  Growers also use vertical tillage to hasten soil drying and warming in wet spring seasons, potentially facilitating earlier or more timely crop establishment.

An external policy factor partially responsible for increasing vertical tillage was an income tax credit that growers could obtain when purchasing “Low-Disturbance Residue Management Equipment,” which included popular vertical tillage tools, through the Resource Enhancement and Protection (REAP) Program sponsored by the Pennsylvania State Conservation Commission (REAP Program Guidelines, 2019).  From 2007-2019, this tax credit incentivized growers to purchase vertical tillage tools to manage residue in no-till cropping systems.  However, a recent 2019 policy change removed the tax credit for vertical tillage tools due to grower use of increasingly more aggressive vertical tillage tools that produce soil disturbance levels that appear to no longer meet policy thresholds for soil conservation.

Our proposed research was designed to improve grower and policy decision-making related to the role of vertical tillage in conservation agriculture by utilizing a multi-criteria assessment to characterize production and conservation tradeoffs of this practice on farms in southeastern Pennsylvania, located within the sensitive Chesapeake Bay watershed.

Cooperators

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  • Dr. Charlie White (Researcher)
  • Dr. Sjoerd Duiker (Researcher)
  • Dr. Paul Esker (Researcher)
  • Jeffrey Graybill (Educator)
  • Leon Ressler (Educator)

Research

Materials and methods:

We conducted on-farm field trials to compare no-till and vertical tillage treatments on nine farms across Lancaster County (n=6) and Chester County (n=3) in southeastern Pennsylvania in 2021 and replicated these on-farm field trials on 12 farms across Lancaster County (n=10) and Chester County (n=2) in 2022.  These cooperating farms consisted mostly of cash grain operations raising corn (Zea mays L.), soybeans (Glycine max L.), winter wheat (Triticum aestivum L.), and winter barley (Hordeum vulgare L.).  Well-drained silt loam soils coupled with frequent manure applications (and occasional applications of spent mushroom substrate) contribute to relatively fertile and historically high-yielding environments on all cooperating farms.  Many of the farms utilize no-till and cover cropping practices.

Experimental Design

On-farm strip trials comparing no-till and vertical tillage were conducted using a nested treatment structure due to variability in tillage legacy and equipment type across farms.  We used tillage management legacy as a grouping factor with two levels: 1) fields where long-term no-till has been practiced for approximately 10 years or more and where vertical tillage was introduced (n=10); and 2) fields where vertical tillage has occurred annually for the previous six to eight years (n=10).  In total, ten tillage treatment comparisons were conducted at locations with each tillage management legacy (with or without a history of vertical tillage), resulting in 20 pairwise tillage treatment comparisons and 40 experimental units.  At each cooperating farm, strip trials were placed in either multiple fields or unique locations within large acreage fields that contain variability in soil conditions and/or terrain. These trials occurred in fields being rotated from corn grain to full-season soybeans.  In these fields, the corn stubble remained unharvested and undisturbed over the winter.  Tillage treatments were employed in the spring prior to planting in paired and randomly located field-length strips that included a no-till (NT) control strip and a vertical tillage (VT) strip.

Diagram of the experimental design

Experimental Design

Field Operations

Farmer cooperators employed vertical tillage using owned or rented implements at an average working depth of 5 cm to manage corn residue in the early spring (April) prior to establishing full-season soybeans.  The vertical tillage tools were compliant with standards for “Low-Disturbance Residue Management Equipment” as defined by the Pennsylvania Resource Enhancement and Protection (REAP) Program Guidelines for fiscal year 2019 (REAP Program Guidelines, 2019).  These guidelines stipulated that qualifying equipment should be set as follows: (1) disc blade angle must not exceed five degrees, (2) disc blades must have no concavity, (3) working depth of equipment must not exceed four inches and (4) minimum surface residue cover must not fall below 60% throughout the year (REAP Program Guidelines, 2019).  Three types of common vertical tillage implements used on cooperating farms included a Salford Independent series tool (Salford Group, Inc., Salford, ON, Canada), a Great Plains Turbo-Till (Great Plains Manufacturing, Inc., Salina, KS), and a Kuhn-Krause Excelerator (Kuhn North America, Inc., Brodhead, WI).

Each cooperating farm implemented standard fertility, seed protection, and crop protection programs for full-season soybeans.  A burndown and pre-emerge herbicide program were implemented on each farm and herbicide product selection was determined by the cooperator or their custom pesticide applicator.  Additionally, all cooperators applied a post-emerge soybean herbicide product(s).  Harvest data was collected using either a yield monitor or by using a weigh wagon or truck scale, and a moisture tester.  Strip width was based on the size of available harvesting equipment so one or two combine passes could be completed within tillage treatment strips.

Data Collection and Data Analysis

1. Soil conservation metric:  The proportion of surface residue cover was determined after vertical tillage treatments are implemented (April) using the line-transect method following the USDA-NRCS standard surface residue cover assessment protocol (Estimating crop residue cover, 1984).

2. Weed management metrics:  We measured winter annual weed abundance in the early spring (April) after tillage treatments were employed and just prior to soybean planting to evaluate the potential for vertical tillage to be employed as a pre-plant weed control tool.  We also measured summer annual weed abundance at the early spring (April) sampling point to assess vertical tillage effects on recruitment of early-emerging summer annual weed species, which may facilitate the use of false-seedbed tactics in no-till systems.  To assess weed abundance, we utilized a belt-transect sampling approach.  Three 15 m transects were established in unique field positions (toe slope, foot slope, backslope) within each strip and co-located between paired strips (i.e., 3 paired transects; 6 transects per paired strip location).  The location of these three paired transects were marked using geo-referencing software (i.e., QGIS) and these locations were used for data collection later in the trial.  Within each transect, the presence or absence of weeds located within 15 cm on each side of the transect was recorded every 15 cm lengthwise.  Presence data was expressed as a proportion of the total number of observations per transect (n=100) as an estimate of weed abundance.  We assessed weed abundance in early summer (June) prior to a POST herbicide application using the same sample methodology to assess recruitment patterns of summer annual weeds and residual herbicide efficacy between no-till and vertical tillage strips.

3. Soybean performance and slug feeding metrics:  Soybean emergence was assessed by measuring the emerged plant population and soybean growth stages when soybean plants reached the Cotyledons Expanded (VC) growth stage.  A 5.3 m long transect (equivalent to 17.5 ft or 1/1,000th of an acre) was established in each strip at each previously georeferenced location. Emerged soybean plants were counted along transects and soybean stand establishment was expressed on a plants per square meter basis.  Soybean stand uniformity was assessed at the time of population assessments using the same transect.  Twenty plants were counted along the transect, their growth stages recorded, and an average growth stage determined.  The growth stages determined at each of the three data collection waypoints within each strip were averaged.  Crop yield was measured using a yield monitor on the combine or by measuring crop mass harvested from each strip using a weigh wagon or truck scale, and a moisture tester.  By measuring crop yield at harvest, we evaluated a tangible and direct result of changing a field management practice.

The incidence of slug damage was assessed in late spring at the V1 to V3 soybean growth stage by establishing two separate transects at each data collection waypoint within each strip.  Within each transect, the number of soybean plants per three meters of row were counted and assigned a slug damage severity rating based on leaf defoliation (%) via slug feeding where 0 = no apparent damage, 1 = 0-25% defoliation, 2 = 26-50% defoliation, 3 = 51-75% defoliation, and 4 = 76-100% defoliation (Douglas & Tooker, 2012).  The number of total plants damaged per three meters of row, and the number of plants damaged based on the ordinal scale, were averaged across the six transects assessed within each strip and expressed as a percentage.

4. Nutrient management metrics:  Soil samples were taken in late fall (October) after soybean harvest was complete to assess nutrient management and soil health metrics (see below).  Within each strip, three soil samples were randomly collected around each georeferenced field position (n =3) used previously for the surface residue cover, weed abundance, and crop emergence metrics.  Soil cores were stratified by sampling depth (0-2.5, 2.5-7.5, 7.5-15 cm) and then composited.  Basic soil fertility analyses was conducted at AASL, including soil pH using 1:1 water extracts (Eckert & Sims, 1982), cation exchange capacity (CEC) using summation of cations (Ross & Ketterings, 2011), base saturation using calculation of cations (Sikora & Moore-Kucera, 2014), extractable phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), zinc (Zn), and copper (Cu) using a Mehlich-3 (ICP) soil extractant (Wolf & Beegle, 2011), and soil organic matter using loss on ignition (LOI) (Schulte, 2011).  Using these soil test results, both pH and soil test phosphorus stratification were assessed.

5. Soil health metrics:  Permanganate oxidizable carbon (POXC) was measured using methods described in Weil et al. (2003), where the active carbon fraction of soil organic matter was oxidized with a weak solution of potassium permanganate (KMnO4).  The assessment was completed by adding 20 mL of 0.02 M potassium permanganate solution to 2.5 g of air-dry soil placed in a plastic centrifuge tube.  The centrifuge tubes were shaken on a mechanical shaker for two minutes at 120 strokes per minute and then placed in a holding rack for ten minutes while soil particles flocculate and settle on the bottom of the tube.  A pocket colorimeter (Pocket Colorimeter II, Hach Company, Loveland, CO) was used to read the absorbance value for the color concentration of the solution with POXC.  The lighter the purple color of the solution with POXC, the less absorbance measured by the colorimeter, the more active carbon in the soil sample which was oxidized.  POXC is expressed as mg C kg-1 soil for each sample.

Microbial respiration was analyzed using the CO2-burst method described in Franzluebbers et al. (2016) to measure the flush of carbon dioxide (CO2) from a sample of air-dry soil re-wetted to 50% water-filled pore space after a 24-hr aerobic incubation in a dark setting at room temperature.  To complete the incubation, 10 g of air-dry soil sieved to 2 mm was placed in a 50 mL plastic beaker and distilled water was added to the top of the beaker to reach 50% water-filled pore space as determined by a previously measured sample specific bulk density.  The plastic beaker was then be placed in a 473 mL (1 pint) glass canning jar sealed with a screw band lid (Ball Corporation, Broomfield, CO) that has a rubber septum installed within the lid and sealed with vacuum grease.  After 24 hours, a syringe was used to extract a 1 mL sample of headspace air from the jar and this sample was injected into an infrared gas analyzer (LI-7000 CO2/H2O Gas Analyzer, LI-COR Biosciences, Lincoln, NE) where the concentration of CO2 in the sample air was compared to that of a reference air with a known CO2 concentration.  The concentration of CO2 in the headspace of the jar was converted to mg C while accounting for the concentration of CO2 in the ambient air in the room when the jars were sealed at the beginning of the incubation.  Microbial respiration estimates were expressed as mg CO2-C kg-1 soil (1 d)-1 for each soil sample.

Wet aggregate stability was assessed utilizing methods described in Kemper et al. (1986), whereby an air-dry soil sample consisting of 1-2 mm sized aggregates was subjected to the disturbance from a wet sieving apparatus and an ultrasonic probe to determine the difference between water stable and water unstable soil aggregates.  For wet aggregate stability analysis, 4 g of air-dry soil 1-2 mm in size were placed in a 0.5 mm sieve and subsequently placed in a wet-sieving apparatus (Five Star Scientific, Twin Falls, ID) and into a pre-weighed metal can filled with 75% distilled water.  The wet-sieving apparatus was mechanically raised and lowered 1.3 cm at a rate of about 35 times per minute, as eight soil samples, each in their respective sieves and cans, were raised and lowered in water for three minutes.  Each soil sample in its respective sieve was then removed from the first set of cans and placed in a second set of pre-weighed metal cans filled partially with distilled water.  These sieves, now inside a second set of metal cans, were placed under an ultrasonic probe as part of a sonifier (Sonifier Cell Disruptor Model W185, Heat-Systems-Ultrasonics, Inc., Plainview, L.I., NY) for approximately 30 seconds that dispersed any remaining soil aggregates into primary particles.  Both sets of cans were placed in a 110°C drying oven overnight to evaporate all water from the cans.  The mass of both sets of cans was recorded and the mass of the dry soil particles from the first set of cans, representing the portion of water unstable aggregates, and the mass of the dry soil particles from the second set of cans, representing the portion of water stable aggregates, was determined.  The percent water stable aggregates (% WSA) in each soil sample was calculated using the following equation:

% WSA = 100 x [Oven dry weight of can B with soil – empty weight of can B] / [(Oven dry weight of can B with soil – empty weight of can B) + (Oven dry weight of can A with soil – empty weight of can A)].

Soil penetration (cone) resistance was also measured at the time of soil sampling in the fall after harvest.  A digital recording penetrometer (Field Scout SC 900 Digital Soil Compaction Meter, Spectrum Technologies, Inc., Aurora, IL) was used to measure soil penetration resistance at three locations around each data collection waypoint within each strip (i.e., nine sampling points total per strip).  Soil penetration resistance in pound-force per square inch (psi) was measured to a depth of 20 cm at 2.5 cm depth increments:  2.5, 5.0, 7.5, 10, 12.5, 15, 17.5, and 20 cm.

Statistical Analysis:  For each response variable described above, we estimated the mean effect size of vertical tillage using linear mixed models by considering tillage treatment, tillage legacy and their interaction as a fixed effect and year, farm (nested within year), and field (nested within farm and year) as random effects.  Mean effect size for each production and conservation metric was reported together to visualize management tradeoffs using our multi-criteria assessment framework.

Research results and discussion:

Vertical tillage effects on soil conservation, weed control, slug damage, and soybean performance metrics

Relative to no-till, vertical tillage reduced surface residue cover, winter annual weed cover, and slug damage but did not influence soybean performance. This study was completed within high-yielding grain corn fields without removing stover and represents one of the highest residue scenarios currently found in row-crop systems in the Mid-Atlantic region. Policy and management implications drawn from this study should be placed in the context of the production environment.

This study found that vertical tillage reduced surface residue cover by 16% points. Other vertical tillage studies with comparable baseline residue conditions found similar reductions in corn residue cover after one pass with a vertical tillage tool (Chen et al., 2016; Conley, 2011; Smith & Warnemuende-Pappas, 2015; Whitehair & Presley, 2010). However, this study showed that the type of vertical tillage tool and the intensity of use significantly impacted the magnitude of vertical tillage effects. Mean surface residue reduction was 26% points when the Kuhn-Krause Excelerator was employed, which resulted in residue cover below state conservation program compliance thresholds (< 60%) in approximately one-third of strips using this tool. Both the design of these tools, and the way in which growers use them, dictates the amount of disturbance created by vertical tillage operations, and therefore residue levels remaining on the soil surface. The magnitude of residue incorporation and soil disturbance can be manipulated by operating the Kuhn-Krause Excelerator at varying depths and disk blade angles with the direction of travel. When operating the Great Plains Turbo Till and Salford tools, the depth of tillage can be adjusted, but disk blade angle cannot be adjusted as the disks on these tools are fixed at a zero-degree angle. This likely added to the observed variability in residue cover as on-farm cooperators were instructed to operate the vertical tillage tools using their standard practice.

Vertical tillage resulted in about a 50% reduction in winter annual weed cover relative to paired no-till strips. While such reductions are not likely to lead to reduction in pre-plant burndown herbicide inputs, vertical tillage could be considered a tool for multi-tactic weed management of winter annual weed species in no-till systems. Well-timed tillage can enhance herbicide-based weed control through additive effects (Buhler et al. 1992), reducing the herbicide resistance evolution rate (Liebman and Gallandt 1997). However, use of fall-sown cover crops provides similar additive effects (>50%) for winter annual weed suppression (Essman et al. 2020; Vollmer et al. 2020; Wallace et al., 2019), are increasingly promoted as a proactive herbicide resistance management tactic (Bunchek et al., 2020), and can provide multiple ecosystem services (Schipanski et al. 2014) in no-till systems. Furthermore, our study highlights the spatial variability of winter annual weed recruitment patterns at field scales (Somerville et al., 2020), which suggests that precision weed management strategies should be favored when developing IWM programs rather than the use of shallow non-inversion tillage tools such as vertical tillage that require implementation at field scales (Buhler, 2002), potentially impacting soil and water quality.

Vertical-tillage resulted in about a 24% reduction in the incidence of slug damage relative to paired no-till strips. Assessing the absolute level of slug damage was more challenging as slug feeding in soybean fields can occur on young seedlings close to the soil surface and partially buried by crop residue (Douglas & Tooker, 2012). Vertical tillage is used by a subset of growers in the Mid-Atlantic region specifically for slug control via residue management. Our results suggest that using vertical tillage tools across large acreages solely for slug management may not be efficient due to patchy distribution patterns within- and among- fields.

Vertical tillage had no effect on soybean population, crop growth stage, or grain crop yield. Other studies measuring impact of vertical tillage on crop yield report varying results. In one study, vertical tillage increased soybean yield (Watters & Douridas, 2013), while another study reported increases in corn yield after vertical tillage but not soybean yield (Van Dee, 2005). Several cooperating farms within this study have invested in planter technologies, such as automatic and pneumatic adjustment of row-unit down pressure and closing wheel systems of various types. These are designed to improve planter performance in heavy corn residue. Such investment may represent an alternative method for maintaining crop performance under higher crop residue environments (Drewry et al. 2021).

Vertical tillage effects on soil pH and nutrient stratification, as well as biological and physical indicators of soil health

While pH stratification across sampling depths and within soil management legacies is statistically significant, it is likely not biologically or agronomically significant due to small differences across depths in the observed fields. Growers participating in this study all maintained regular lime additions, which can alleviate the acid roof symptoms that are sometimes reported in no-till systems. In fact, in this study, legacy no-till farms exhibited the opposite phenomenon, an ‘alkaline roof,’ where due to recent lime additions, the 0 – 2.5 cm depth segment had a higher soil pH than the lower depth segments. Indeed, prior to the start of the project, several legacy no-till farms applied limestone to the fields which were to be studied. Over time, the soil in this layer would be expected to acidify following the addition of nitrogen fertilizer and due to crop residue decomposition.

No vertical tillage treatment or soil management legacy main effects alleviated nutrient and organic matter stratification found across sampling depths in the no-till and vertical tillage fields in this study. A single vertical tillage pass performed in the spring, or repeated vertical tillage passes over time, did not substantially move soil test P or other nutrients deeper in the soil profile. Nutrient stratification is a potential management tradeoff in no-till systems (Beegle, 1996), which can influence soil nutrient fate in the environment. Results from other no-till and vertical tillage studies affirm soil test P stratification with higher soil test P occurring near the soil surface (Sharpley, 2003). In no-till cropping systems with a history of surface-applied manure applications, increased losses of soluble P in agricultural runoff are observed (Maguire et al., 2011). While decreases in soluble P runoff due to vertical tillage would be beneficial (Smith & Warnemuende-Pappas, 2015), results from this study indicate that shallow non-inversion tillage is not aggressive enough to alter the P stratification observed in the fields in this study.

Regarding biological indicators of soil health, a sampling depth main effect was observed for soil organic matter, active carbon (POXC), and microbial respiration. Higher concentrations of soil organic matter and POXC, and higher rates of microbial respiration, were found near the soil surface and these values decreased with depth. POXC, the fraction of labile carbon often considered to be the readily available carbon pool for utilization by soil microbes, decreased with depth. In the same way, microbial oxidation of carbon was quantified using the CO2-burst method described earlier, and the quantity CO2 respired by microbes decreased with depth as well. In addition, a tillage treatment by sampling depth interaction existed for POXC.

Though increases in the total quantity or distribution of soil organic carbon throughout the soil profile is an indicator of improved soil chemical and biological function, this study was not able to confirm that either occurs because of short- or long-term vertical tillage. With escalating public and private interest in evaluating and quantifying on-farm soil health, and burgeoning interest in soil C sequestration, measuring organic matter and carbon stratification, as well as microbial respiration, is pertinent and could guide quantification and verification efforts. As growers begin to receive ecosystem service payments for practices that sequester soil carbon, such as no-till soil management, questions will likely surface whether implementing vertical tillage affects soil carbon sequestration capacity. Results from this study indicate no difference in soil organic matter levels due to soil management legacy. Additionally, POXC should be relatively sensitive to short-term changes in soil management practices such as vertical tillage compared to other soil carbon pools, while organic matter should be indicative of long-term soil management practices.

Regarding physical indicators of soil health, a soil management legacy by sampling depth interaction was observed for aggregate stability and soil penetration resistance. Aggregate stability decreased with sampling depth and this reduction was greater in the long-term vertical tillage legacy relative to the no-till legacy. The greatest reductions in aggregate stability occurred within the zone of soil mixing and below the working depth of the vertical tillage tools in this study.

Differences in soil penetration resistance were observed across soil management legacies. In the long-term no-till legacy, surface hardness was detected as penetrometer values were higher at shallower depths than in the vertical tillage legacy. When interpreting soil penetration resistance values, a generally accepted threshold used to indicate soil compaction occurs when values exceed 300 pound-force per square inch (psi; Duiker, 2002). In the vertical tillage legacy, penetrometer values were lower near the soil surface in the zone of soil mixing performed by the vertical tillage tool but reach the 300-psi threshold at a shallower depth than in the no-till legacy. These results suggest that a compacted layer or ‘hard pan’ may be developing below the working depth of vertical tillage tools used in this study and commonly used in the Mid-Atlantic region.

Wet aggregate stability and soil penetration resistance are important physical indicators of soil health as they relate to soil structure and compaction. Past studies indicate a subsurface compaction layer may be created by vertical tillage at or below the working depth of the tool (Gameda et al., 1985). While some studies found inconclusive results related to whether surface crusting is alleviated or created in no-till soils due to vertical tillage (Blanco-Canqui et al., 2009), results from this study suggest vertical tillage may loosen the top few centimeters of soil and create a compacted layer with repeated tillage over time.

This project is discussed at length in the following Thesis: [Lefever] Production and conservation tradeoffs of vertical tillage_MS Thesis_11-22-22

Research conclusions:

Results from this two-year, on-farm strip trial study in corn residue in southeast Pennsylvania suggest that vertical tillage can reduce surface residue cover below state conservation compliance thresholds (<60%), depending on equipment type and aggressivity of use, and may have marginal utility as integrated weed management (IWM) or slug management tools. While vertical tillage may locally influence residue cover, weed control, and slug damage, the effect is likely not large enough to substantially alter chemical weed management or mitigate slug damage. In addition, vertical tillage did not improve soybean stand establishment or soybean grain yield.

Results from this study also indicate that vertical tillage may alleviate soil pH stratification but may not be aggressive enough to alleviate phosphorus or soil organic matter stratification as was hypothesized. Further, vertical tillage did not reduce no-till stratification of active C (POXC) or microbial respiration (CO2-burst). Additionally, long-term vertical tillage may alleviate surface crusting but may also create a compacted layer at a shallow depth relative to compaction found in soils under long-term no-till management.

Participation Summary
16 Farmers participating in research

Education & Outreach Activities and Participation Summary

16 Consultations
1 Journal articles
4 Webinars / talks / presentations
3 Workshop field days

Participation Summary:

180 Farmers participated
100 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

Outreach activities engaged in to date include:

Summer Soil Health Field Day facilitated by Pennsylvania No-Till Alliance, July 2021, Lancaster County, PA

-Presentation on project design and initial results of vertical tillage study followed by panel discussion on benefits/tradeoffs associated with vertical tillage

Summer Soil Health Field Day facilitated by Pennsylvania No-Till Alliance, July 2021, Butler County, PA

-Presentation on project design and initial results of vertical tillage study followed by panel discussion on benefits/tradeoffs associated with vertical tillage

Soybean Grower Meeting facilitated by Pennsylvania On-Farm Network, Lebanon County, PA

-Breakfast meeting with Penn State faculty, Penn State extension educators, and local crop growers discussing pertinent issues in soybean production including vertical tillage practices; shared project design and initial project results

Vertical Tillage Project - Year 1 Summary Meeting facilitated by Penn State Weed Science Program, Lancaster County, PA

-Lunch meeting with Penn State faculty, Penn State extension educators, and on-farm cooperators involved in the vertical tillage project to thank the growers for their help and summarize initial findings from year 1 of the vertical tillage project

Vertical Tillage Project - Year 2 Summary Meeting facilitated by Penn State Weed Science Program, Lancaster County, PA

-Lunch meeting with Penn State faculty, Penn State extension educators, and on-farm cooperators involved in the vertical tillage project to thank the growers for their help and summarize initial findings from both years of the vertical tillage project

Farming for Success - Summer Field Day facilitated by Penn State Extension, Lancaster County, PA

-Two presentations were made, one session in the morning and one session in the afternoon, at Penn State's Landisville Experiment Station regarding year 1 results of the vertical tillage project

Keystone Crops and Soils Conference facilitated by Penn State Extension, Dauphin County, PA

-Summary presentation for the project titled Vertical Tillage Effects on Crop Production and Pest Management

 

A manuscript summarizing the research outcomes from the first part of the vertical tillage project (i.e., soil conservation, pest management, and crop production metrics) has been submitted to the Agronomy Journal and is currently under review:

Lefever, A. M., Wallace, J. M., Esker, P. D., White, C. M., Duiker, S. W., Tooker, J. F. (2023). Vertical tillage effects on crop production and pest management in Pennsylvania. Agronomy Journal. (in review)

 

Initial outreach objectives still in progress:

Results from this project will be shared by graduate student Andrew Lefever with growers and agricultural professionals in Pennsylvania and the Northeast using multiple extension-outreach platforms accessible through cooperation with extension-research scientists who served as mentors for the project and are members of the Penn State Extension Agronomy team. Written outreach products will include (1) a Penn State Field Crop News newsletter article, (2) a Pennsylvania On-Farm Network newsletter article, and (3) a Lancaster Farming newspaper article.

A second manuscript summarizing the research outcomes from the second part of the vertical tillage project (i.e., soil pH and nutrient stratification, as well as biological and physical indicators of soil health) is planned for future submission.

Project Outcomes

Project outcomes:

While no direct quantitative measures may be available to assess the effects of this study on agricultural sustainability over time, it is our hope that as information related to the vertical tillage project is shared, crop producers will consider the tradeoffs associated with vertical tillage.  It is our hope that crop producers will understand and accept that several of the perceived benefits of vertical tillage do not exist.  It is our hope that crop producers will consider whether this form of minimum tillage in otherwise no-till cropping systems is worthwhile from an economic and environmental perspective.

Knowledge Gained:

In response to our study, farmer cooperators emphasized the utility of vertical tillage to quickly prepare seedbeds before planting as they attempt to achieve timely crop establishment under challenging springtime weather conditions. The ability of vertical tillage to hasten soil warming and drying, allowing producers to establish crops earlier, should be a topic of future research. In addition to seedbed preparation, producers also perceive an ability of vertical tillage to incorporate manure or fertilizer and alleviate surface compaction. Extending on-farm evaluation of vertical tillage to other production regions, and under alternative crop management (e.g., planting date) scenarios, is needed to fully characterize its effects on cash crop performance.

Assessment of Project Approach and Areas of Further Study:

Questions remain regarding the tradeoffs associated with re-introducing a form of minimum tillage into an otherwise no-till system for the purposes of seedbed preparation, manure or fertilizer incorporation, compaction alleviation, or improvement of soil health, and these questions merit further investigation as producers and researchers seek a crop production model that is profitable and conservation-minded.

Therefore, items of further research could include studying the effects of vertical tillage on soil erosion potential, water and nutrient runoff, water infiltration, as well as early season soil temperature and moisture changes as indicators of soil warming and drying.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.