Water-soluble cations in shoot dry weight of common bean and balance of ions in the soil in response to the magnesium application

The increased magnesium (Mg) concentration in vegetables may be reduced due to inter-ionic inhibition caused by the concentration of other water-soluble cations that are mainly associated to low molecular weight organic anions. However, it is not known whether the levels of these compounds in crop residues are modified by increasing the Mg soil application. This study aimed to assess the effects of the Mg application on the contents of water soluble cations potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), cooper (Cu²⁺), iron (Fe²⁺), manganese (Mn²⁺), and zinc (Zn²⁺)] on common bean plant residues. The experiment was conducted under greenhouse conditions with Ustoxix Quatzipsamment in completely randomized design in 4×5 factorial scheme, with three replicates. The treatments consisted of four rates of Mg 0, 50, 100 and 200 mg kg^?1, source magnesium chloride (MgCl₂)] and five varieties of common bean of the carioca group BRS Estilo, BRS Ametista, IPR Campos Gerais (CG), IPR Tangará and IAPAR 81]. The Mg rates affected the contents of water soluble Ca²⁺, Mg²⁺, Cu²⁺, Fe²⁺ and Mn²⁺ in the extracts of bean residue. The soluble Mg²⁺ showed a significant correlation with foliar Mg content, indicating the need for further research on the method used to assess nutrient availability in vegetables. The bean varieties showed different responses regarding balance of ions in cation exchange capacity (CEC) and in the Ca/Mg, Ca/K and Mg/K ratios in the soil.