Influence of Calcium and Magnesium Salts on Acid Soil Chemistry and Calcium Nutrition of Apple

Abstract

AbstractField experiments were conducted in two Brazilian orchards to examine the effects of soil applications of calcitic lime (Ca‐lime), phosphogypsum, CaCl2, and magnesite (Mg‐lime) on soil chemistry and Ca nutrition of apple (Malus domestica Borkh. cv. Gala/MM 106). One orchard was on a low Ca, high Al Inceptisol; the second orchard was on a low Ca, low Al Oxisol. The resulting soil chemical changes were strongly influenced by the initial soil chemistry and the composition of the soil amendments. The effects of Ca‐lime, added at a rate calculated to neutralize the topsoil exchange acidity, were restricted primarily to the upper 20 cm of the soil, where it increased pH, increased total dissolved and exchangeable Ca, eliminated dissolved Al, and reduced exchangeable Al. Phosphogypsum, added at Ca rates equivalent to the Ca‐lime treatment, slightly reduced soil pH in the Inceptisol and slightly increased soil pH in the Oxisol. Phosphogypsum did not appreciably affect dissolved Al in the topsoil; however, it did reduce exchangeable Al but to a lesser degree than did Ca‐lime or Mg‐lime. Phosphogypsum increased exchangeable Ca and decreased exchangeable Al in the subsoil to a depth of 40 to 60 cm. Calcium chloride, added at Ca rates equivalent to the Ca‐lime treatment, produced dissolved and exchangeable Ca increases similar to the phosphogypsum treatment; however, soluble and exchangeable Al were increased and pH slightly decreased throughout the soil profiles. Mg‐lime, added at an acidity‐neutralizing rate equivalent to the Ca‐lime treatment, produced results similar to Ca‐lime except that soluble and exchangeable Mg rather than Ca were increased in the topsoil. Apple tree root densities were enhanced in the soil layers that were made simultaneously high in exchangeable Ca and low in exchangeable Al by the soil amendments. The trees with the more extensive root systems had higher leaf Ca concentrations and produced more and larger fruit. The Ca concentrations in these larger fruit were not reduced by fruit expansion, suggesting enhanced Ca supply from the soil