Phytoextraction of Cadmium Using Solanum nigrum and Bidens pilosa: Comparative Evaluation and Effect of Planting Distance in Theobroma cacao L. Producing Areas in Northeastern Peru

Cacao (Theobroma cacao L.) is a crop of great economic importance in Peru; however, the presence of cadmium (Cd) in cacao-growing soils limits its production and international trade. The objective of this study was to evaluate the effect of Solanum nigrum (black nightshade) and Bidens pilosa (cobbler’s pegs) on Cd removal in cacao-producing areas of northeastern Peru. The research was conducted using a completely randomized block design (CRBD) with two factors: the phytoremediation species and planting distance (30, 50, and 70 cm), in four production areas: La Concordia 01, La Concordia 02, La Lluhuana, and La Chorrera. The reduction in Cd in soil, roots, and cacao beans was evaluated, as well as the accumulation of the metal in leaves (30, 60, 120, and 150 days) and roots (120 and 150 days) of the phytoextracting species, in addition to the bioconcentration factor (BCF) and translocation factor (TF). Cd reductions were recorded in the soil, with a maximum decrease from 0.81 to 0.03 mg kg−1 (La Chorrera). In roots, the greatest reduction was from 1.79 to 0.69 mg kg−1 (La Concordia 02), while in beans it was from 1.65 to 1.08 mg kg−1 (La Chorrera). BCF values ranged from 1.12 to 6.97, with TF > 1, showing differences among the evaluated sites. Overall, the study findings demonstrate that the phytoextractive response was more related to site conditions than to the species used or the planting distance.