Evaluating the on-farm environmental and economic impacts of the use of aerators with liquid and semi-solid manure under various management conditions

Final Report for ONE10-126

Project Type: Partnership
Funds awarded in 2010: $14,907.00
Projected End Date: 12/31/2012
Region: Northeast
State: Vermont
Project Leader:
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Project Information


The purpose of this project was to determine if the use of an aerator incorporating manure on permanent hayfields with multiple passes of the aerator throughout the growing season had an effect on forage yield, quality and quantity. If there was an effect was it to the benefit or detriment of the crop when using a semi-solid manure system as compared to a liquid manure system on a farm scale level.

While the extreme weather of 2011 likely influenced agronomic factors, there appeared to be no differences in forage yield, density, quality, or soil tests. There did appear to be a difference in surface compaction based on a statistically significant difference in year 1, but not in year 2. There was a difference in soil health assessments over the two years of the study. There were also changes in the Cornell Soil Health Tests between the plots but there is not enough evidence to say conclusively that it was due to aeration. This suggests a need for continued evaluation of soil compaction with a penetrometer, and ongoing soil health assessments that look at multiple soil health factors.


Farmers are struggling to stay in business with low milk and beef prices, increasing fertilizer costs, increasing fuel costs and increasing equipment costs. They are also facing an increase in scrutiny from both the regulatory and private sectors on their potential to pollute. This scrutiny comes from an increase in public awareness on water quality issues, primarily public beach closings due to toxic algae blooms in the northern sections of Lake Champlain. The main reason given for the algae blooms is the excessive nutrient content, specifically phosphorous, in the lake and extensive funding and resources have been given to addressing this concern. While this is critical in the north lake, the lake flows from south to north and nutrient issues in the south lake can dramatically affect the north lake segments.

The south lake watershed of Lake Champlain consists of 1400 square miles, and is the most impaired area of Lake Champlain for phosphorus after St. Albans and Missiquoi Bay (Lake Champlain Basin Program, Progress 2006). This region includes the drainages of the Poultney and Mettowee Rivers, the Otter Creek and the Lower Lake Champlain Direct drainage. The watershed of the Poultney and Mettowee Rivers is estimated to contribute 13.6% of the phosphorus in the lake at the most southern end of which an estimated 35% is from agriculture; Otter Creek watershed has approximately the same contribution levels (LCBP, Atlas). The south lake region has phosphorus levels that have not met targets set by the New York and Vermont governments for the past five years. In addition, there is no trend towards improvement (LCBP, State of the Lake, 2005).

While it has been well documented that timely manure incorporation will reduce runoff of nutrients as well as increase nitrogen availability to crops, traditional incorporation on hay land is not possible. Several studies have documented reduced nutrient runoff with the use of field aeration prior to liquid manure application, however, it is unclear if soil aeration will reduce or improve the yield and stand health of perennial forages. It is also unclear if there is any benefit, or detriment, when using an aerator with semi-solid manure systems. There is also conflicting information as to how often a field should be aerated. According to the Vermont Agency of Agriculture’s Farm Agronomic Practices Program and USDA/NRCS CCPI grant, the field must be aerated prior to every manure application in order to receive monetary cost share. According to representatives from Aerway and GenTill, fields should be aerated no more than once or twice a year depending on soil type.

Through this project, we looked at the use of aerators for incorporation of manure on a farm scale level for both liquid and semi-solid manure systems, aerating a field more than once in a growing season, and at overall stand health and density. It is only by demonstrating the value of this equipment in the local environment and with local management techniques that farmers are willing to try a new practice. Participating farms are located throughout Rutland County and have a diversity of soil types and management strategies.

Description of Equipment:

Aerators are pull-behind machines that create vertical slits in the soil that open up the soil for better water and nutrient infiltration and decrease compaction at the surface, at least on a temporary basis. Think of an upside down triangle. At the tipping point between moving down through the soil then back up, the tine will give a slight twist which is thought to create a shattering effect in the soil to decrease compaction. Our Gen-Till II units have 5 different settings depending on how much soil disturbance is desired: 0, 2.5, 5, 7.5 or 10 degrees. 0 is limited soil disturbance and 10 degrees is a lot of soil disturbance. On hay ground the 0 or 2.5 degree settings are the most common settings to use. If incorporating manure on corn ground, the 7.5 or 10 degree settings are most common. Most farms find that using the units at roughly 4-6 mph is appropriate, but that can also depend upon terrain and soil moisture. Aerators should not be used on wet fields as they will cause damage.
The general rule of thumb is that a tractor will need to have 10hp per foot of unit and will need to have hydraulic hoses to raise and lower the machine. The horse power needed is also dependent upon if the tractor is 2wd or 4wd, the amount of soil compaction present, if additional weight is needed, and the topography of the land. A hilly field will require more horsepower than a flat field.

Project Objectives:

Evaluate use of aerators for incorporation of manure on the farm scale level. Four farms participated. The following anecdotal information has been shared with farmers while data is being collected:

• Two farmers who used the 15’ aerator on hard clay felt the GenTill was too light. They preferred the Aerway even when weights were added to the GenTill.
• The holes created by the aerator in clay soils seemed to close up more quickly than the sandy or silty loams which surprised us. This was evident when the Hamlin Silt Loam plot was flooded several times and holes were still visible where as the Vergennes Clay plot closed up quickly.
• Aeration on wet soils can be very detrimental by tearing up sod
• Farmers with severe compaction felt the aerators were extremely beneficial in helping to mitigate this concern.
• No apparent affect to the crop stand with multiple passes of the aerator (maximum of 3) though it is necessary to evaluate winter kill to confirm
• Clover seemed to thrive with the disturbance, though this must be replicated in different growing seasons for confirmation
• No definitive differences were seen in crop yield (both anecdotally and in research plots). Several farmers felt that it was valuable to disturb the roots of permanent sod
• Small aerator was very effective as a tillage tool for reseeding a hayfield
• We did not feel we had any data that could definitively conclude exact runoff control. We had our intern in the field watching manure after several rain events. Flow was influenced by manure consistency, amount of forage in the field and rate of application, but manure never seemed to “flow” directly into holes. Measurement of exact infiltration is beyond the scope of this research project; however we will continue visual inspections.
• We secured funding to continue the project through the growing season of 2011 from the Lake Champlain Basin Program


Evaluate use of aerators for incorporation of manure on the farm scale level Four farms participated. The following anecdotal information has been shared with farmers:

• The two farms that used both the Aerway and GenTill units felt that the GenTill unit pulled fewer stones.
• There were differences in the penetrometer readings between the control, 1, and 2 pass plots, and the 3 pass plots. Dr. Sid Bosworth discussed a possible statistical difference based on a 10% probability, but did not send documentation.
• As with 2010, there was no definitive difference seen in crop yield both anecdotally and in research plots.
• As in 2010, we did not feel we had any data that could definitively conclude exact runoff control. Flow was influenced by manure consistency, amount of forage in the field and rate of application, but manure never seemed to “flow” directly into holes.
• Provide information and education to farmers in the area about the project as well as overall recommendations to use the aerator as a best management practice.
• Two aerator demonstrations were held in August. One at a research farm in Clarendon on August 12th, and the other at a non-research farm in Wells on August 22nd.

1. Evaluate data collected in 2010 and 2011

• A workshop was held on March 7th to discuss the Year One results of the Aerator trials. This workshop was held at the East Poultney Baptist Church.
• A presentation was given at the UVM Agronomy Plus meeting in Poultney on February 8th 2012 highlighting what was found during the 2 year of this trial.
• The presentation was shared with UVM Agronomy Conservation Assistance Program staff. Jennifer Alexander was on hand to answer any questions concerning aeration and this project at the UVM Agronomy Plus meeting in Vergennes, VT.


Click linked name(s) to expand/collapse or show everyone's info
  • Bruce Anderson
  • Bruce Anderson
  • Jeff Carter
  • Cash Ruane
  • Art Seward
  • Jeff Sheldon
  • Dr. John Van Hoesen


Materials and methods:

Test plots were set up on four farms in Rutland County, VT to evaluate differences in soil health, stand health, and forage yield and quality on grass fields with one, two or three passes of the aerator and a control plot that received no aeration. Sites were chosen based on farmer willingness, site accessibility, characteristics (representative of Rutland County agriculture) and ability to maintain plot consistency. The goal was to determine the value of the aerator in this type of agriculture, focusing on Rutland County soils, topography and farm management practices.

Diagrams of layouts on each farm are in the Test Plot Setup images uploaded below this section. All plots were on perennial cropland with side-by-side plots that allowed for an experimental and control area. Size of plots varied between farms based on the size of the aerator used (15’ or 8’9”) but were consistent within farms. Plots were randomly chosen. Three sample plots were created on three farms with four on one farm (last farmer only cuts twice per year, so this ensured 12 sub-plots per farm). Each plot had three to four subplots:
1. Control ( no aerator use)
2. Aerator used once during growing season.
3. Aerator used twice during growing season.
4. Aerator used three times during growing season (where applicable).

Aeration was done before manure application with liquid manure and after with semi-solid manure.

Farmer education and outreach was a major component of this project with the objective of increasing farmer interest in and implementation of this technology. Farmer turnout at most events was good, and the ability to showcase this equipment in a visible area and with numerous events resulted in increased use of the aerator. However, it is clear from farmer comments that aerator use will be directly connected to the availability of cost-share funds, since the current price of fuel and feed is a substantial impediment to use of this equipment without immediate visible results and more long-term benefits.

[ A diagram of farm plot layouts and a diagram of farm location in relationship to the county can be found in the PowerPoint presentations uploaded below.]

Research results and discussion:

The research and data collection part of the project went mostly according to plan for the two years of trials. After analyzing 2010 forage yield data, it became apparent that collecting the wet weight of forage harvested in the sample plots was not sufficient and a Koster forage tester was purchased so dry weight equivalents could be measured in 2011along with wet weights.

The 2011 season proved to be challenging for data collection and farming in general. First cut data was not collected because by the time crops could be harvested, they were lodged and so soggy that the data was considered inadmissible. Third cut was also a challenge due to Tropical Storm Irene. The test plots on one farm were completely underwater for several weeks in September of 2011. Remarkably the flags in the plots were not lost in the floodwaters, however the extremely high ash content in forage tests were indicative of the damage and sedimentation.

The primary results are not strong enough to support experiences by other farmers as to the runoff benefits and yield increases of aerator use. However, this study was done on sandy soils with little or no slope (most common type of farming environment in Rutland County) and results could easily be different in clay or hilly situations. The results do indicate a need for additional research to evaluate the benefits of decreased surface compaction with aeration, and its contribution to soil health which could be substantial and valuable over the longer term. The challenge there is the education to support this. Soil health is proven to be of strong long-term value to farm sustainability, however in tight economic times, and with the current price of fuel and feed, it will take education to convince farmers that the short-term expense of aeration is worth the long-term soil benefit.

Research conclusions:

What we learned from this project, both technical (related to data collection) and farmer input are listedd below. The technical data is undoubtedly influenced by the unique and enormous implications of the 2011 weather, both the exceptionally wet spring and the impact of Tropical Storms Irene and Lee.

Technical Conclusions

• Year 1 indicated a statistical difference in penetrometer readings between the Control/1pass/2pass plots and the plot with 3 passes. Year 2 data did not indicate a statistical difference in the penetrometer readings. However, the Soil Health Assessments, which evaluate over the two years of the study, indicated a change in surface compaction in some test plots. Year 2 data may have been influenced by the wet soil conditions which increase machinery pass compaction.

The question of soil aeration relieving soil surface compaction arose when this project started and was one that we wanted to explore further. In spring 2011 and 2012 each replication and subplot was tested using a soil penetrometer to measure soil tension. The generally accepted practice is that when soil compaction reaches 300 psi according to a penetrometer, plant roots will have to expend more energy in order to push through the soil.

The attached chart shows at what depth the 300 psi is reached in the soil at each location. Sid Bosworth, Phd., discussed that the 2011 readings showed a statistical difference at a 10% probability between the control, one and two passes compared to three passes, but did not provide hard copy documentation of such. There was no difference in the 2012 readings. The following should be taken into consideration when looking at the charts: Samples each year were taken in April, the summer of 2011 was fairly wet and many farms were driving on fields that were too wet in order to harvest their crops, the winter of 2011-2012 was mild with very little snow fall and mild temperatures leading to little frost action, and the spring of 2012 was wet. Soil moisture can affect penetrometer readings. In 2011, 4-5 penetrometer readings were taken while in 2012, that number was increased to 10 as it was suggested that our sampling set was too small and that we may be taking readings within aerator holes.

• There was no statistical difference in forage yield or growth between test plots for both years. In year one there appeared to be a visual increase in clover growth in the aerated plots versus the control. Clover counts were included in 2011 under the direction of Dr. Sid Bosworth. However in 2011 there was no difference in clover growth, and the increase the previous year was attributed to normal crop variations (temperature, moisture, etc) after discussions with other farmers and agricultural professionals.

• There was no discernible difference in forage quality between plots.

• There was no discernible difference in soil tests.

• It was impossible to accurately measure fuel use on plots – plot size would have to be large enough to justify topping off fuel tank between plots. Farmers have commented that the price of fuel currently is a major impediment to using an aerator and adding further machinery expenses to their crop management plans is a burden.

• P-index and RUSLE calculations were done. However, the P-index does not include a scenario for the value of aeration as it could not be used as a comparable tool.

• There was no decrease in soil organic matter or negative effects to grass forage stands regardless of the number of passes with the aerator. This was a concern expressed by local farmers prior to this study.

Lessons learned/Farmer input

This information is valuable as an educational resource to other farmers based on the wide range of experiential information included.

• Aeration on wet soils can be very detriment by tearing up sod

• Aerating the soil at too fast can be detrimental by tearing up sod

• Farmer with severe compaction felt that aeration was very beneficial

• The holes created by the aerator in clay soils seemed to close up more quickly than in sand or silty soils which was a surprise. This held true even after several flooding events on a sandy loam soil

• While some farmers in other parts of the state have attempted to quantify the runoff control potential of aeration, we did not feel we had any data that could definitively conclude exact runoff control. Our intern visually watched manure after several rain events, to evaluate infiltration. Flow was influenced by manure consistency, amount of forage in the field and the rate of application, but manure never seemed to “flow” directly into the holes.

• Some farmers who had used the aerator in other settings indicated that they felt aerating helped a field or pasture that is “sod bound” by promoting new root growth, and would help pastures where plowing does not normally occur to decrease compaction.

• We could see a benefit in using the aerator with a rotary harrow attachment to create a better seed bed in an annual crop field rather than disking. There is other research data that shows that repeated disking can create a pan layer if plowing does not also occur.

• The test plots generated a lot of local farmer interest and talk. The best way to get the word spread through the farming community is through trials and demonstrations such as funded by this grant.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

One of our goals was to provide information and education to farmers in the area about the project as well as overall recommendations and best management practices for use of the aerator.

• Articles about the project were included in three issues of the Spreading Times newsletter which reaches 700 producers and partners.
• A field day was held at one of the participating farms on October 12, 2010 to demonstrate the aerator and discuss the project.

• A workshop was held in March 2011 for farmers
• Two aerator demonstrations were held in August 2011.
• Presentation given at two UVM Agronomy Plus meetings in February, 2012

Educational materials developed include:
• Two powerpoint presentations (end of Year 1, Year 2)
• Brochure for farmers
• Tabletop display

Power Point Presentations, informational/educational brochure, poster display used at meetings and workshops.

Project Outcomes

Project outcomes:

Farmer Adoption

What we have learned is that most farms, unless there is cost-share available for the practice, have little incentive to use the aerator in Rutland County. On the silt loam/sandy loam soils there is no perceived “bang for the buck” over the short term. The new farms that have used the aerator, tend toward the smaller grass based farms to break up perceived surface compaction in pastures and create some soil disturbance when planning on frost seeding in spring. We feel that there is enough preliminary data to suggest that there could be a long term benefit for permanent sod fields in the reduction of surface compaction. This needs to be more closely studied to determine what sequence of aeration needs to be followed for long term reduction in surface compaction.

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.