Farm-fabricated on-farm composting equipment project: Aerating equipment

2006 Annual Report for ONE05-036

Project Type: Partnership
Funds awarded in 2005: $9,980.00
Projected End Date: 12/31/2007
Matching Non-Federal Funds: $20,182.00
Region: Northeast
State: Vermont
Project Leader:
Tom Gilbert
The Highfields Institute

Farm-fabricated on-farm composting equipment project: Aerating equipment


The Farm-fabricated On-Farm Composting Equipment Project is an effort to increase the availability of affordable composting technologies to farmers in order to further promote the more widespread integration of composting and compost use in agriculture. SARE funds will be used for the aerating equipment section of this project, in which we will focus on developing two significantly different aerating technologies.

One design is an attempt to make the concept of the commercially-available, tractor-drawn windrow turners more economically accessible. The second design modifies a conventional front-end loader bucket into an aerating bucket that aerates the pile with bucket-mounted tines. The implement designs will be tested, modified, trialed, and assessed on common parameters. A two-page product comparison of these implements and other equipment for aerating compost will be compiled.

Fabrication manuals will be developed for each implement design. The manuals will be available for the cost of copying or as a free download. An extensive outreach program will enable us to share these designs with farmers and advertise the availability of the fabrication manuals.

Objectives/Performance Targets

  • Increase the adoption of on-farm composting by addressing equipment cost and management time issues that have been identified as primary limiting factors in the wide spread adoption of composting as a manure management practice.

    Develop two different pieces of compost aerating equipment that can be fabricated on the farm using existing farm equipment and implements to the greatest extent possible.

    Make the two different pieces of equipment represent different levels of capital investment, levels of fabrication difficulty, and approaches to aeration to meet the diverse needs of different farms.

    Make these equipment designs available to farmers through fabrication manuals to help address farmers’ concerns about the investment of time and/ or capital in considering on-farm composting.

    Inform farmers about the availability of these designs and their associated fabrication manuals through two on-farm demonstrations, exhibits at agricultural conferences and events, posters, and agricultural media.


As previously mentioned, we have most recently been focusing primarily on the turner fabrication, which is nearly complete, as well as the fabrication manuals which are progressing steadily but still in the early stages of development. Additionally, our work to date has included research, networking, concept development, design work, materials strength calculations, soliciting equipment donations (tractor and pay loader buckets), and inventorying the availability of used agricultural equipment parts and components at dealerships and parts yards. We have also been developing the design and testing parameters for each piece of equipment. The design parameters were developed by our design team to keep the designs effective, as easy to fabricate and replicate as possible, affordable, and practical. The testing parameters were and continue to be established with the assistance of other professionals and researchers in the composting industry in order to establish common and meaningful ways by which we evaluate the effectiveness of each aerating implement. Some of these efforts have set us back on the original timeline for the project, but have also increased the capacity of the project to yield high quality, replicable designs and more user friendly fabrication manuals.

Our networking and research efforts have yielded contacts in the US and Canada for farmers using commercial and farm-fabricated tractor-drawn windrow turners, as well as collaboration with the Vermont Technical College Engineering Department and other non-profits exploring similar areas of work. Through our collaboration with the VTC Engineering Department we have received technical assistance from the faculty and students in calculating the load bearing capacity required for the tines on the aerating bucket designs and in creating CAD drawings to detail the design of the turner and the fabrication steps for the fabrication manuals. In addition to the VTC Materials’ Strength class calculating the size of the tine stock required for aerating windrows with the aerating bucket, the class developed an interactive calculator that can be used by farmer-fabricators to size out different stock based on pre-established variables integrated into the excel program.
This program will not only help us in the design and fabrication process of the aerating bucket, but will allow us to post this calculator to our website as an interactive tool for farmer-fabricators and other metal workers in designing variations on our design concept based on salvaged and other materials available to them, their bucket size and other variables that effect the size of the tine stock required.

In working on the windrow turner we have focused on learning from the commercially available designs, identifying replicable strengths and avoidable weaknesses in their designs, as well as opportunities to use components from existing farm equipment to utilize in the design and fabrication. We also made an effort to explore previously developed designs for farm-fabricated turners. We were able to find several farmers, agricultural degree programs and farm-related non-profits that have developed their own windrow turner designs, however we found that most of these designs were either not practically replicable or did not work. In many of the cases in which the system did not work, the turner had been made by retro-fitting an existing piece of farm equipment. It seemed that many of the short-comings of these designs were the result of design factors that were inherited by the original equipment design. Additionally, many of these retro-fitted pieces of equipment were not commonly available, such as old flail choppers. As a result our design team determined that the turner would be most replicable for farmers now and in the future if we built the turner frame from scratch (using as much salvaged steel as possible) and use specific parts and components from commonly available farm equipment, such as drive systems, drums, and PTO-drives.

In order to source parts and components from commonly available farm equipment, we have been informally inventorying equipment dealers and yards in Vermont for various types of equipment that our design team has identified as being promising for salvaging specific components from. For example, we have determined that the augers used in feed mixing wagons are a commonly available part that may be able to be used as the turner drum on the windrow turner. The turner drum would be a difficult part of the design to fabricate on the farm, and therefore salvaging it makes the final design more easily fabricated by most farmers, and therefore a more practical design for widespread adoption. Feed mixer wagons are common pieces of equipment and many of them use a similar auger design to mix the grain and move it toward the discharge trough. Therefore, utilizing the auger from feed mixers provides us with a practical drum part that is easily replicated in the future by others. There is some concern that the diameter of these augers will be undersized for the use as a turning drum. As a result of this uncertainty, as well as a desire to experiment with various drum configurations, the turner prototype will be designed to have the drum be removable.

Another area of inquiry that we have endeavored on in developing the turner, is how farms that do not have hydro-static tractors or tractors with a “creeper” gear will be able to move through the pile slowly enough to prevent dragging the turner. After learning from Vermont farmers of some on-farm innovations in Canada to put “creeper” gears on tractors that lack it, our fabricator took a trip to Ontario to meet with the farmer and learn from his developments. This same farm has fabricated a windrow turner that seems to be performing well and meets many of our design guidelines. Our fabricator, Frank Sauer, brought back some excellent insights from his trip that have been applied to our design, as was also able to visit farmers in New York to see their commercial turners.

In developing the aerating bucket, we have decided to develop designs for standard tractor buckets and pay loader buckets. The designs will draw upon the same principles, but will be designed with their differing volume capacities in mind. We were successful in soliciting donations of a tractor bucket (Northeast Farm Service) and a 2-yard loader bucket (Case) to modify. We have begun working on the tractor bucket and have devised ways to trial various design options without cutting into the bucket until we have the final design established. In figuring out how to prevent cutting into the bucket, we decided that it may be most effective to develop an implement that can be mounted to, and detached from, an in-tact bucket. This would enable farmers to utilize their existing tractor buckets without having to purchase a new one or modify an existing one for aerating compost. We continue to explore our design options with the aerating bucket and have not determined if this will be the direction the final design goes in. There may be structural or performance factors that indicate a benefit from removing some of the bucket floor.

In working on the bucket design, we have trialed one design with two different tine materials to date. This design included four foot tines mounted to the top side of the bottom plate of the bucket with U-bolts on 8” and then 16” spacing (we initially started with the 8” spacing but found it was to close, so we removed every other tine to achieve a 16” spacing). We tried using 1 ¼” solid cold-rolled steel rods and 1 5/16” galvanized tubing (1/8” wall) for the tines. While both sets of tines eventually bent at the blade edge of the bucket on this design, and the tractor was unable to lift them through dense parts of the pile from bottom to top in one try, we were encouraged to find that in the least dense areas of the windrow the tines were able to be lifted through the material, did have the desired aerating effect when lifted through the pile, and exceeded our expectations in their mixing effect on the pile contents. In the areas of the pile that were too dense for the tines to be lifted through the pile in one motion, we found that if we started at the top of the pile and lifted the tines through one third of the pile at a time, we could achieve the desired effect. While in both instances the tines eventually failed after 20-30 minutes of work, it should be recognized that these failures were experienced after working with the tines on an eight inch spacing for some time. The problem with the close spacing was that since the compost mix that the bucket was being used on had a moderate amount of hay and the material would bridge the tine spacing as the bucket was lifted through the pile, causing the tines to lift the entire contents of that section of pile, rather than lift and sift through it as intended. Therefore, we believe the tines were unnecessarily compromised in the initial period of the trial, and may have performed better and longer with the wider spacing. We anticipate applying VTC tine stock recommendations shortly in a similar configuration and will begin trialing the design this winter.

At this time we expect to complete the initial fabrication of the designs in the next two months and begin trialing them by March. We hope to be prepared to finalize the designs in the spring. Recognizing that the basic development of the fabrication manuals does not require completed designs, we have begun the process of developing the format, core contents, and other aspects of the fabrication manuals. Our hope is that by starting the manuals before fabrication and trials are complete, we will be able to complete and print the manuals shortly after the design has been finalized. This timeline would allow us to begin our outreach and education program in early summer 2007.

Impacts and Contributions/Outcomes

We are in the process of completing the program implementation phase of the project right now, having completed most of the initial fabrication and not yet having begun any trials or outreach. Our progress has mostly been focused in developing designs, finding technical resources, networking with other organizations and individuals, carrying out literature and product research, developing a template for the aerating bucket, working with design communications and materials strength classes in the Vermont Technical College Engineering Program to develop extensive portfolio of CAD drawings of the turner and a table of metal stock dimensions for the tines on the aerating bucket, sourcing new and used parts for the turner, fabrication of the turner, and beginning to develop the fabrication maunals. We have shared our preliminary work on the aerating bucket with the 60 attendees at the Highfields Institute’s Open House, largely farmers and professionals in agriculture, waste management and water quality. Through our design development work we have networked and collaborated with roughly nine farmers (two farmers are partners on the project), four Vermont Technical College (VTC) Engineering Department faculty, approximately 20 VTC engineering students, three composting industry professionals and researchers, and four farm and construction equipment dealers.

Through our networking and research efforts we have been able to identify key design features for each piece of equipment. For both pieces of equipment the cost and ease of fabrication, as well as the more obvious aspects of performance, were critical features to consider.

Some of these for the Windrow Turner include:
prevent dragging the far side of the turner/ have turner track parallel to path of tractor despite resistance in the pile,

maximize aerating and mixing effect of the turner drum while minimizing its macerating effect on organic matter,

single pass turning is critical to maintain time efficiency,

minimum of five foot tall frame,

ability to raise and lower turner drum hydraulically.

Some of the key design features for the aerating bucket include:
tine strength capable of lifting through roughly 4,000 pounds,

tine system that can potentially be attached and detached from a bucket without modifying the bucket,

tine lengths of 48” if possible in order to penetrate the pile core,

ability to move in and out of the pile with ease