Chemical Species and Aluminum Concentration in the Solution of Acid Soils Cultivated with Soybean and Corn under Liming

Abstract

ABSTRACT Chemical speciation of the soil solution is an important tool to identify Al species related to phytotoxicity. In some Brazilian acid soils, the Al extractable by the KCl 1.0 mol L -1 solution (Al-KCl) exceeds 10 cmol c kg -1 and even then, in some situations, it does not cause toxicity to the plants. This study aimed to evaluate the relationship between these high concentrations of Al-KCl found in some Brazilian acid soils and the activity of the different Al chemical species in the soil solution, as well as the response of soybean and corn plants to lime application. Subsurface horizon (B) samples of five soils were collected in four states of Brazil (AC, PE, RS, and SC) from areas that had never been cultivated. The samples were then given increasing rates of limestone, equivalent to that required to neutralize 0, 0.25, 0.5, and 1.00 times the contents of H+Al and were incubated for 98 days. After that period, the soils were fertilized and planted to soybean and corn in the greenhouse for 60 and 45 days, respectively, in 2015. The experimental units consisted of 8 L pots, filled with 5 kg of soil (dry basis). After each crop, the plants and soil samples were collected to determine the leaf, stem, and root dry matter, and chemical composition. In the soil solution, cations and anions, pH, electrical conductivity, and dissolved organic carbon were quantified. The distribution of the Al species was evaluated using the program Minteq. Free Al (Al 3+ ) was the species found in highest proportion in treatments without limestone, in all soils. Application at the lowest limestone rate, equivalent to 25 % of that required for H+Al neutralization, was sufficient to decrease Al activity in the soil solution to levels considered non-toxic to plants in four of the five soils. High levels of Al-KCl are not related to manifestation of toxicity and to Al 3+ activity in the solution of Hapludult (Acre profile 9; AC9) and Hapludult (Rosario do Sul; RS) since dry matter (DM) production in these soils was little influenced by liming, unlike what occurred in the Hapludult (Pernambuco; PE), Humudepts (Bom Retiro; BR), and Kandiudox (Curitibanos; CB) soils, in which Al-KCl contents were related to Al activity in the solution and to DM production of the plants grown in them.

Keywords

• chemical speciation
• phytotoxicity
• production of plants
• aluminum activity