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

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.

摘要 土壤溶液化学形态分析是鉴定与植物毒性相关铝形态（Al species）的重要手段。在部分巴西酸性土壤中，1.0 mol·L⁻¹氯化钾溶液提取态铝（Al-KCl）的含量超过10 cmol_c·kg⁻¹，但在部分场景下并未对植物产生毒性。本研究旨在评估巴西部分酸性土壤中检出的高浓度Al-KCl与土壤溶液中不同铝形态活度之间的关联，以及大豆与玉米植株对石灰施用的响应。
研究采集了巴西4个州（阿克里州AC、伯南布哥州PE、南里奥格兰德州RS、圣卡塔琳娜州SC）5块从未开垦区域的亚表层（B层）土壤样品。随后向土壤施加梯度递增的石灰用量，分别相当于中和0、0.25、0.5及1.00倍的H+Al含量，并培养98天。培养结束后，于2015年在温室中对土壤进行施肥，分别种植大豆与玉米，种植周期分别为60天与45天。试验单元为容积8 L的盆钵，每盆装入5 kg干基土壤。每茬作物收获后，采集植株与土壤样品，测定叶片、茎秆与根系的干物质重量及化学成分。对土壤溶液中的阴阳离子、pH、电导率及溶解性有机碳进行定量分析，采用Minteq软件评估铝形态的分布特征。
在未施用石灰的处理组中，所有供试土壤的优势铝形态均为游离铝离子（Al³+）。施加最低梯度的石灰用量（相当于中和25%的H+Al所需用量），即可使5份供试土壤中的4份土壤的溶液中铝活度降至对植物无毒性的水平。在Hapludult（阿克里剖面9号，AC9）与Hapludult（罗萨里奥杜苏尔，南里奥格兰德，RS）土壤中，高含量的Al-KCl与植物毒性表现及溶液中Al³+活度均无关联，因为这些土壤的干物质（dry matter, DM）产量几乎不受石灰施用的影响；而在Hapludult（伯南布哥，PE）、Humudepts（邦雷图，BR）及Kandiudox（库里蒂巴诺斯，CB）土壤中则与此不同，Al-KCl含量与溶液中铝活度及种植作物的干物质产量均存在关联。