Two composts, a Malian (C1) and a Belgian (C2), and a peat substrate (C3) were analyzed for their suitability for land application. The results revealed that the materials can be used in agriculture but only the composts can supply all macro-nutrients necessary for plant growth. The fractionation of Mn, Fe, Zn and Cu in operationally defined fractions (water soluble, exchangeable, complexed, organically bound and residual) allows estimation of the availability of metals for uptake. For example, 16% of the total Mn in the composts (C1 and C2) and 22% in the peat substrate would be plant available. Available Fe in the three materials was less than 2%. Available Zn varied from 10% to 25%. The fractionation also allowed estimation of the potential for contamination of groundwater following the applications of composts to agricultural lands.