Influence of Long-Term Application of Organic and Mineral Fertilizers on Quality of a Savanna Alfisol

The soils of the West African savanna are low in physical and chemical productivity. One conventional method of improving productivity of these soils is through application of organic materials either as a supplement or an alternative to mineral fertilizers. In terms of physical and fertility properties, the agricultural value of this practice is unquestionable. However, its influence on trace and heavy metal accumulation in the soil needs to be determined for the practice to be considered sustainable. This study investigated the occurrence of some trace and heavy metals in the topsoil of an Alfisol under 45 years of application of cowdung (D), nitrogen (N), phosphorus (P) and potassium (K) at Samaru, Nigeria. Results showed soil texture ranging from sandy loam to loam. Higher soil surface bulk density were observed for D, DN, K and NPK treatments, however, the DNPK treatment recorded a lower soil surface bulk density averaging 1.44 Mg m−3. Treatments with cowdung generally recorded a higher saturated hydraulic conductivity. None of the trace and heavy metals analyzed attained values that indicate serious contamination (i.e., intervention values) except for chromium (Cr), whose values indicate heavy contamination in soils of DN and DP treatments, thus reducing their quality. On the basis of soil quality and the physical properties considered, the long-term DNPK treatment provides the most sustainable agricultural practice. Since it recorded lower values of trace and heavy metals relative to the other treatments.