Composts (e. g., from green and kitchen waste) and soil differ in their compo­sition and properties in almost every parameter. The amount of organic carbon, the amount of organic nitrogen, pH, electrical conductivity (EC), cation exchange capacity (CEC), salinity, chloride concentration, and sulfate concentration are higher in compost. Therefore, depending on the quality and quantity of compost, climate, and soil characteristics, their application will result in a modification of the soil organic matter composition (Fuchs et al. 2004). Compost application increases soil organic carbon and total nitrogen content at the upper horizon in both sandy and clay soils, and that increase can be observed even more than 10 years after application (Melero et al. 2007; Delschen 1999). Generally, an increase in soil pH after compost use is observed because most composts are basic and have a considerable buffering capacity. The mineralization of carbon and the subsequent production of OH~ ions by ligand exchange as well as the introduction of basic cations such as K+, Ca2+, and Mg2+ leads to an increase of soil pH (Mkhabela and Warman 2005). Compost application can ameliorate soil acidity by increasing soil pH and allows large quantities of lime required for these soils to be saved (Haynes and Mokolobate 2001). Application of municipal, mixed green and animal waste compost has been reported to proportionally increase the EC and salt effects of soils (Stamatiadis et al. 1999; Walter et al. 2006). Agricultural soil EC levels ranged from 0 to 4 dS m-1, whereas soil EC levels of municipal solid waste composts ranged from 3.69 to 7.49 dS m-1 (Brady and Weil 1996); therefore, the increase of EC could be of concern. In some cases, soil EC levels were excessive and inhibited plant growth; nevertheless, Zhang et al. (2006) reported that the increased soil EC values decline over time because of nutrient removal by crops and leaching, but the long-term soil biological activity could be negatively affected (Iglesias-Jimenez and Alvarez 1993). Incorporation of compost into soil, especially at high doses, increases the CEC (Bengtson and Cornette 1973); the rise is generally linked to an increase in the level of organic material, the pH, and in base saturation (Ca, K, Na) (Fuchs et al. 2004). Nitrate leaching is one of the concerns regarding compost utilization. NO3~ is highly mobile in soils and is susceptible to leaching through the soil profile and into the groundwater by the infiltrating water. When compared with organic and mineral fertilizers, the nitrate leaching potential of composts is very low (Insam and Merschak 1997). Composts for agricultural use should come from source-separated organic waste and green waste only; then heavy metals are not of concern, as they would be if municipal solid waste compost were used (Epstein et al. 1992; Sharma et al. 1997).