July 25, 2007 | General

The "Bionic" Compost Spreader

BioCycle July 2007, Vol. 48, No. 7, p. 57
Unit developed in Central Texas proves how much a spreader can restore damaged training lands and improve rangeland health on this 260,000 acre reservation.
M. Scott Keating

If “necessity is the mother of invention,” then the Pilot Revegetation Project at Ft. Hood in Central Texas gave birth to what might be considered the “immortal compost spreader.” From 2003 to present, the Texas Water Resources Institute (TWRI), Blackland Research and Extension Center (BREC), and the USDA Natural Resources Conservation Service (NRCS) have been partnering with the U.S. military in a consorted effort to restore damaged training lands and improve rangeland health on this 260,000-acre reservation.
The project was awarded the Governor’s highest environmental citation in the Agriculture Division given by the Texas Commission on Environmental Quality for 2006. It was born of a two-fold need to remove composted dairy waste from an ecosystem containing too much elemental N and P and transferring that excess to an ecosystem needing additional fertility. Restoration posed a logistical challenge in distributing a composted dairy waste onto the rugged military training lands.
It became quickly apparent that a standard agricultural distributor would not withstand the punishing terrain of the training grounds of Ft. Hood. So what began as sketches on a napkin from conversations between Drs. Bill Fox and myself at TWRI moved forward into plans and specifications with Ricky Lloyd at High Roller Manufacturing in Bryan, Texas, to design and construct a very special compost spreader.
The designers elected to build a 10-cubic yard capacity tongue-pull prototype to operate from a 3-point hitch. Tractor horsepower was arbitrarily set in the 100-hp neighborhood, mostly for height and visibility needed to view craters and gullies on the training lands. A 40-ton axle with twin 20 inch by 22 inch tires was selected from an 18-wheeler body with the thinking that, at any one time, all 10 tons or so of the payload would be settling onto one axle as rugged terrain tossed the equipment about.
A ground clearance specification of 31 inches was selected in lieu of the standard 12-15 inches on most agricultural equipment. A stainless steel body was constructed to accommodate even the most caustic of materials. Downside angles inside the box were increased to handle the occasional high-moisture load so that the payload material would fall properly without the necessity to enter the bed body with shovels to unload the compost.
One thing led to another as specifications were beefed up with a 31-inch discharge chain and over-sized distribution spinners. Whenever standard discharge chains called for 1-inch sprockets, specifications were increased to 1-1/2 inch sprockets, all requiring custom fabrication.
Spinners can either be immobilized or removed to distribute extra-heavy application rates in concentrated areas. Treatment application rates of the dairy compost for the Pilot Revegetation Project ranged from 5 cubic yards per acre to 90 cubic yards per acre.
Autonomous hydraulics allow for added versatility in choices of drive equipment. Overall buggy height was compromised to allow for standard front-end loader capabilities and still maximize payload capacity.
Real-life compost application taught the research team that ideally a 3-buggy system allows the efficiency of a loader driver to remain in place without dismounting and remounting other equipment. While presenting research results at various soil and water meetings, the team has received interest as far away as Canada in this “mother of all compost spreaders”.
In a report on the project written by Kathy Wythe, researchers with TWRI in College Station and BREC in Temple determined that composted dairy manure can increase soil fertility and vegetation cover on some of the Fort’s 200,000 acres of training areas and stabilize eroded soils without excessive nutrients entering the streams. Dr. Fox and Dennis Hoffman – the pilot project’s coleaders – with 20 other scientists and land managers have established more than 500 acres of R&D sites.
“We needed to know that the compost applied on Fort Hood’s land is not causing nutrient problems in the water and demonstrate that nutrients in compost can be turned into something positive – growing grass and reducing soil erosion,” Fox said. “We’ve seen nothing to indicate runoff of nutrients into streams,” Hoffman said, whose team monitors water quality. “After two years of comprehensive work on multiple sites, our research has demonstrated that sites receiving 15 or more cubic yards per acre of compost along with reseeding treatments have produced significant vegetation increases,” Fox notes.
The compost not only adds nutrients and organic matter to the training land’s soil but it also improves the soil’s structure, increases its water-holding capacity and aids in erosion control. To date, the project has trucked in more than 15,000 tons of compost from the North Bosque River Watershed where too much phosphorus from dairy manure runoff is impairing that watershed.
“The unique character of this project,” said Fox, “is that two major environmental problems are being addressed at the same time. Excessive nutrients in one watershed are being used to fertilize nutrient-starved soil in another. Two ‘bads’ can make a ‘good.'”
The group compared the percent of change in ground cover, bare ground and litter (leaves and dead biomass on the ground) over time: 1) at the start of the project, 2) one year after compost was added, and 3) 18 months after compost treatment, which was also after one year of training on the site. The amount of ground with no vegetation decreased from 50 percent to 32 percent one year after compost treatment and decreased even further to 24 percent, 18 months after treatment. Fox attributed this decrease to the litter that remained on the ground after training maneuvers.
The research shows that it takes 12 to 18 months after compost and seed application to achieve significant changes in plant basal cover, Fox points out. Preliminary analysis indicates that the treated sites are also more resilient after training exercises than before compost was added, continues Wythe.
Scott Keating is a research scientist for the Texas Water Resources Institute. In addition to his work on TWRI’s Rangeland Revegetation Project for Fort Hood, Texas, Keating also is involved with an Environmental Infrastructure Project for the North Bosque River and the Land-Use Management Impacts Flood Control Project in North Harris County. He can be reached at

Sign up