Composting with a clay cap

The University of California-Riverside composts 1,700 to 2,000 tons of landscaping material every year in a system that has been used for at least four decades. The main feedstock is yard trimmings generated by maintenance of turf shrubbery and trees on the 320-acre campus. Yard trimmings are either used for mulch or taken to the almost three-acre compost site and formed into static piles about six feet high with tractors. The piles are capped with a sixto eight-inch layer of clay soil three or four times during the composting process. "You have to mix compost with soil anyway," says Robert Giese, assistant director of physical plant and landscape refuse services. Water is added once …