The application of biochar in soils is a well-established strategy to improve their physical and chemical properties, but the effects should be evaluated for each soil particularly. This study was conducted in a greenhouse of the Agricultural Sciences Unit (ASU) of Rio Grande do Norte Federal University (UFRN), in Macaiba, RN, Brazil, to evaluate the effect of biochar addition to sandy soil. The experiment was carried out in 10-L pots in a completely randomized design with four doses of biochar (0, 3500, 7000, and 10,500kgha(-1)) and four replications. The soil was collected from the top layer of a field adjacent to ASU and the biochar feedstock was wood from pruning cashew trees. The pots were cultivated with upland rice (Oryza sativa L.) and cowpea (Vigna unguiculata (l.) Walp.) in succession. The soil was sampled at 150 and 220days after application of the treatments. The soil variables determined were pH, soil organic matter, contents of phosphorous (P), potassium (K), and calcium (Ca) plus magnesium (Mg), in addition to cation exchange capacity and exchangeable sodium percentage. Statistical analysis of experimental data included analysis of variance of the effect of biochar and regression analysis for variables with significant effect of those doses. The biochar obtained from cashew tree wood used in the experiment showed potential for use as a soil conditioner, since pH and K and P contents increased with rising doses of biochar. However, using this type of biochar can pose a risk regarding salinization, as indicated by the increase in exchangeable sodium percentage (ESP).
