Biochar amendment to agricultural soils has been promoted for use in agricultural systems, both to mitigate global warming by increasing long-term soil carbon (C) sequestration and to enhance soil fertility and crop productivity. The objective of this study was to evaluate the effects of a single biochar application from peanut shell (Arachis hypogea L.) and mixed pine (Pinus spp.) wood to a Typic Hapludults in Blacksburg (VA, USA) and from peanut shell and eucalyptus (Eucalyptus camaldulensis) wood to a tropical, sandy, salt-affected soil in Ndoff (Fatick, Senegal) at 0, 10, and 20 Mg ha⁻¹ on soil chemical properties, inorganic nitrogen supply, and pearl millet production responses under field conditions for two growing seasons (2014 and 2015). Biochar application to temperate soils (Blacksburg) significantly increased total soil carbon, nitrogen, and plant available potassium in both years. In addition, pearl millet yields significant increased (53%) at the 20 Mg ha⁻¹ rate of peanut shell biochar in 2014 but did not persist in year 2. Beneficial effects largely appeared due to nutrient additions. Biochar treatment to tropical, sandy, salt-affected soils (Ndoff) had no effect on soil chemical properties. These results suggest that biochar application could improve soil fertility and crop productivity in temperate soils but had limited effects on tropical, sandy, salt-stressed soils in this study. The disparate results between these two field studies could be explained by differences in soil properties and climate, biomass feedstock, pyrolysis processes, and biochar handling, as well as experimental set-up.