For millennia, the thundering hooves of millions of American bison churned up the prairie soil, helping rejuvenate the prairie grasses on which the bison grazed. With the decimation of the bison in the late 1800s, this symbiotic relationship vanished and the remaining tracts of prairie no longer flourish as they once did.
But a Boone, Iowa, company, with assistance from the U.S. Department of Energyâ€™s Ames Laboratory, developed and built a mechanical land â€œimprinterâ€ designed to imitate the action of bison hooves to help promote growth of prairie grasses and forbs. The imprinter was specially built for the U.S. Fish and Wildlife Service for use in prairie restoration at the Rocky Mountain Arsenal National Wildlife Refuge, a 17,000-acre preserve northeast of Denver that was formerly a remediation site from the manufacture of chemical weapons and pesticides.
Mid-States Steel normally produces a variety of custom-built structural steel components such as heavy steel framing including large trusses and special fabrications for building and industrial uses. According to company president Doug Kollbaum, the company was looking to diversify its business and through contacts with potential agricultural and industrial customers, he found out about an interesting potential project with the Fish and Wildlife Service.
â€œThey were looking for someone to build a special roller that would leave indentations in the ground similar to bison hoof impressions,â€ Kollbaum said. â€œThese impressions catch and hold moisture, particularly in areas with minimal rainfall, and improve prairie seed growth.â€
The FWS was looking for a 13-foot-wide roller-type implement that could be pulled behind a tractor. Staggered rings of angular â€œteethâ€ around the rollerâ€™s circumference would make the impressions. But how heavy would the roller need to be to make the necessary impressions in the dry Colorado soil?
To help answer that question, Mid-States turned to the Iowa State University Institute for Physical Research and Technology's Company Assistance program. IPRT Company Assistance connected Mid-States with the Ames Laboratory Engineering Services department and provided funding to conduct the project.
â€œAmes Labâ€™s Terry Herrman assisted us to determine the machine weight needed for Colorado soil conditions,â€ Kollbaum said. â€œWe worked on the preliminary frame and roller design and then utilized Ames Lab's assistance with stress analysis of the assembly before proceeding with fabrication.â€
According to Herrman, Mid-Statesâ€™ initial design used a box-type frame which proved to be inadequate during computer model stress testing, given the requisite weight of the roller.
â€œWe tried using arched steel beams above the roller and got a much better result,â€ Herrman said. â€œThen we tried adding a steel skin and bracing to the arches to make it even stronger, and thatâ€™s what was eventually used on the roller.â€
The final design was approved by the FWS and Mid-States set about building it. The 38-inch-diameter roller is hollow and contains no center shaft. It can be filled with fluid or sand to boost its weight from 9,000 pounds up to 12,000. An additional payload can be added to the frame to boost the imprinterâ€™s weight to 15,000 pounds â€“ roughly the same as eight bull bison.
The Mid-States Steel LI-1013 land imprinter was delivered to the Rocky Mountain National Wildlife Refuge in December. According to FWS Rangeland Manager, Terry Wright, "Using this implement will create a soil surface texture once created by millions of roaming bison. Because of the unique micro-environments it creates, it should greatly improve the establishment success of the native prairies we are seeding."
The land imprinter is one of a number of unique projects in which Ames Labâ€™s Engineering Services has been involved. A few years ago, the department helped design and build a machine to simulate the pressure and friction created by glaciers for Iowa State University geology professor Neal Iverson.
â€œWe enjoy the challenge of working on these types of unique projects,â€ Herrman said. â€œBeing a national laboratory, we understand the importance of materials engineering and can bring our expertise to bear in solving problems that companies donâ€™t normally encounter.â€
Kollbaum concurs, adding, â€œWithout Ames Lab's assistance Mid-States would not have proceeded with the project. Their expertise filled the gap to provide the missing information we needed.â€