A REVIEW AND EVALUATION OF LITERATURE PERTAINING TO COMPOST CHARACTERISTICS AND TO THE APPLICATION OF COMPOST ALONE AND MIXED WITH DIFFERENT SOILS

The Texas Department of Transportation (TxDOT) reports that composted manures have been used in 22 of the 25 TxDOT districts, usually with excellent results. The application of composted manures to rights-of-way successfully improved growth of vegetation and controlled erosion of slopes on highway embankments. However, consistent availability of compost of the quality and quantity required for use in roadside projects is problematic in some states. Many sates have adopted specifications for compost characteristics to ensure consistent quality of compost. The objectives of this literature evaluation are identification of the constituents and composition of various types of composted materials including animal manures, municipal wastes (solid waste and wastewater sludges), and other waste materials, as well as documentation of application of the composted materials alone as well as mixed with different soils (composted manufactured topsoil). Most compost has a pH in the neutral range, organic matter content ranges from 30% to 60%, moisture content ranges from 30% to 50%, and the concentrations of N, P, K, and salts are higher than those typically found in agricultural soils. Compost addition to soil is considered Compost Manufactured Topsoil (CMT). CMT has improved soil structure, reduced bulk density, increased permeability, and increased aggregate stability compared to soil alone. These improvements reduce erosion and increase the water holding capacity of CMT. CMT also increased availability of soil nutrients, microbial population and activity, and reduced the incidence of soil nematodes and other pathogens. Potential problems with compost use include water quality impacts caused by nutrient loss and leaching of high salt concentrations, as well as potential accumulation of heavy metals in the soil zone.