Mineral and organo-mineral fertilization alters soil Ca–Mg–K balance and base saturation during early coffee establishment

<ns3:p> Exchangeable-cation ratios and cation exchange capacity indices can capture early shifts in soil base-cation balance during coffee establishment. We assessed calcium (Ca), magnesium (Mg) and potassium (K) balance in a newly established Arabica coffee field (Coffea arabica L., cultivar Acaiá IAC 474-19) in Indianópolis, Minas Gerais, Brazil, on a clayey dystrophic Red Latosol, comparable to a Ferralsol and an Oxisol. A randomized complete block 3 × 4 factorial compared planting fertiliser sources, mineral fertiliser (MIN, 11-52-00), poultry-manure organo-mineral fertiliser (OMF-CF, 06-30-00) and filter-cake organo-mineral fertiliser (OMF-TF, 06-30-00), combined with four rates of a poultry-based organic fertiliser (2, 4, 6 and 8 t ha? <ns3:sup>1</ns3:sup> ), with four blocks. Treatments were applied once in the planting furrow (Day 0), seedlings were transplanted on Day 40, and soil (0–20 cm) was sampled 90 days after transplanting (Day 130); pre-application samples provided site characterisation. Exchangeable Ca, Mg and K and potential acidity (hydrogen plus aluminium, H+Al) were used to compute cation ratios and proportions relative to cation exchange capacity at pH 7.0 (T), including base saturation (V). Factorial analysis of variance with Tukey’s HSD (p ≤ 0.05) showed Source × Rate interactions for nine of ten indicators; K/T showed no interaction. Relative to the site baseline (V 58%, Ca/T 40%, H+Al/T 42%), all treatments increased V at Day 130 (66–77%) and reduced H+Al/T (23–34%). OMF-CF at 8 t ha–1 achieved the highest V (77%) and Ca/T (66%) and the lowest H+Al/T (23%), but also the highest Ca/Mg (7.1) and Ca/K (37), indicating potential cation-imbalance risk. OMF-TF responses were limited across rates (V 71–75%), whereas MIN showed non-monotonic patterns. Baseline values were not plot-specific; inference is based on among-treatment comparisons at Day 130. </ns3:p>