title: Nickel Availability in Soil as Influenced by Liming and Its Role in Soybean Nitrogen Metabolism.
abstract: Nickel (Ni) availability in soil varies as a function of pH. Plants require Ni in small quantities for normal development, especially in legumes due its role in nitrogen (N) metabolism. This study investigated the effect of soil base saturation, and Ni amendments on Ni uptake, N accumulation in the leaves and grains, as well as to evaluate organic acids changes in soybean. In addition, two N assimilation enzymes were assayed: nitrate reductase (NR) and Ni-dependent urease. Soybean plants inoculated with Bradyrhizobium japonicum were cultivated in soil-filled pots under two base-cation saturation (BCS) ratios (50 and 70%) and five Ni rates - 0.0; 0.1; 0.5; 1.0; and 10.0 mg dm(-3) Ni. At flowering (R1 developmental stage), plants for each condition were evaluated for organic acids (oxalic, malonic, succinic, malic, tartaric, fumaric, oxaloacetic, citric and lactic) levels as well as the activities of urease and NR. At the end of the growth period (R7 developmental stage - grain maturity), grain N and Ni accumulations were determined. The available soil-Ni in rhizosphere extracted by DTPA increased with Ni rates, notably in BCS50. The highest concentrations of organic acid and N occurred in BCS70 and 0.5 mg dm(-3) of Ni. There were no significant differences for urease activity taken on plants grown at BSC50 for Ni rates, except for the control treatment, while plants cultivated at soil BCS70 increased the urease activity up to 0.5 mg dm(-3) of Ni. In addition, the highest values for urease activities were reached from the 0.5 mg dm(-3) of Ni rate for both BCS treatments. The NR activity was not affected by any treatment indicating good biological nitrogen fixation (BNF) for all plants. The reddish color of the nodules increased with Ni rates in both BCS50 and 70, also confirms the good BNF due to Ni availability. The optimal development of soybean occurs in BCS70, but requires an extra Ni supply for the production of organic acids and for increased N-shoot and grain accumulation.
authors.affiliation: Center for Nuclear Energy in Agriculture, University of Sao Paulo Piracicaba, Brazil.
authors.forename: Fernando G
authors.initials: FG
authors.lastname: de Macedo
authors.affiliation: Brazilian Agricultural Research Corporation São Carlos, Brazil.
authors.forename: Joana D
authors.initials: JD
authors.lastname: Bresolin
authors.affiliation: Center for Nuclear Energy in Agriculture, University of Sao Paulo Piracicaba, Brazil.
authors.forename: Elcio F
authors.initials: EF
authors.lastname: Santos
authors.affiliation: Center for Nuclear Energy in Agriculture, University of Sao Paulo Piracicaba, Brazil.
authors.forename: Felipe
authors.initials: F
authors.lastname: Furlan
authors.affiliation: Brazilian Agricultural Research Corporation São Carlos, Brazil.
authors.forename: Wilson T
authors.initials: WT
authors.lastname: Lopes da Silva
authors.affiliation: University of Missouri, Columbia MO, USA.
authors.forename: Joe C
authors.initials: JC
authors.lastname: Polacco
authors.affiliation: Center for Nuclear Energy in Agriculture, University of Sao Paulo Piracicaba, Brazil.
authors.forename: José
authors.initials: J
authors.lastname: Lavres
keywords: base-cation saturation; grain nitrogen accumulation; micronutrient; nickel; nitrate reductase; soil rhizosphere; urease