Temporal changes in basic cations in soils under cocoa cultivation in the Brazilian Atlantic forest

Low base saturation causes abiotic stress in crops. However, it can be a significant factor for increasing yields when adjusted to appropriate levels. This study aimed to assess the temporal alterations of basic cations in two soil layers under cocoa tree cultivation in the Brazilian Atlantic Forest biome. For this purpose, a seven-year field experiment was established, consisting of 19 experimental areas (EAs), each of which received superficial applications of lime and agricultural gypsum. The changes on basic cations levels were measured at doses of 0.36-1.09 and 0.29-2.69 t ha-1 limestone and gypsum, respectively, after 0, 40, 52, 72, and 87 months of application. In the first two years, the cocoa trees were fertilized with the N-P-K 16-16-16 formula in doses of 640 and 1,025 kg ha-1, respectively, divided into four applications. Nutrition was done with monoammonium phosphate, urea, triple superphosphate and potassium chloride as source. The results suggests that in most EAs, lime did not affect Ca2+ and Mg2+ levels, consequently, causing no difference on the base sum and base saturation in the 0–20 cm layer. However, gypsum led to increase of Ca2+ levels in both soil layers, as well as an increase of Mg2+ and K+ levels in the 20–40 cm layer. Variations in K+ levels were associated with potassium fertilization. Cocoa producers should apply gypsum to enhance the chemical properties of poor soils by increasing exchangeable base levels at greater depths. This improvement promotes deeper root growth, enabling cocoa trees to access a larger soil volume and better withstand water stress during drought periods.