Evaluation of certain Ni soil tests for an initial estimation of Ni sufficiency critical levels

Abstract

Although Ni is officially recognized as an essential micronutrient for all higher plants, the majority of the published research on soil availability of Ni focuses on its hazardous role as a heavy metal. The objective of the study was to evaluate certain Ni soil tests in uncontaminated soils for an initial estimation of its sufficiency critical levels. Nickel was extracted from 30 cultivated soils employing the following extraction methods: DTPA, AB-DTPA, AAAc-EDTA, Mehlich-3, 0.1 M HCl, and 0.1 M HNO 3 . Ryegrass (Lolium perenne L.) was grown in pots containing the soils, harvested five times, certain plant parameters were determined, and the Cate-Nelson procedures were used for Ni critical levels determination. Among the six methods, HCl was the least reliable extractant for the evaluation of soil available Ni, whereas the most significant (p ≤ 5%) relationships between Ni concentration or Ni uptake by ryegrass and Ni soil tests were consistently obtained for AAAc-EDTA or Mehlich-3 extractable Ni. In many cases, > 80% of the variability of Ni concentration or uptake by ryegrass was explained by these two soil tests without the inclusion of other soil properties that affect Ni bioavailability. Sufficiency critical levels of Ni in soil were ≈ 2 mg kg -1 for both methods. Consequently, as an initial approach, concentrations of AAAc-EDTA or Mehlich-3 extractable Ni < 2 mg kg -1 are probably a good guide to indicate soils that will respond to Ni fertilization.

Assessment of nickel's sufficiency critical levels in cultivated soils, employing commonly used calibration techniques

“…3c, d). These values were at similar levels to those assessed in our previous work utilizing the same technique ( Nikoli and Matsi , 2014).…”

“…Ten out of 30 soils, which had been used previously in a pot experiment for evaluation and initial calibration of Ni soil tests with ryegrass ( Nikoli and Matsi , 2014), were used in the current study. At the end of this experiment, Ni was extracted from the 30 soils with the AAAc‐EDTA ( Sillanpää , 1990) and Mehlich‐3 ( Mehlich , 1984) methods, in duplicate.…”

“…Nickel was added to the soils at four rates and the original and Ni‐treated soils were used in a pot experiment with ryegrass. The physical‐chemical properties of the 10 soils, which were determined by Nikoli and Matsi (2014), are reported in Table 1.…”

“…Nickel was added to 2.5 kg of each of the 10 soils in the form of an aqueous solution of NiSO 4 at rates of 1, 2, 4, and 8 mg Ni kg −1 of soil. These application rates were chosen to approximate previously assessed Ni sufficiency critical levels ( Nikoli and Matsi , 2014), i.e ., ≈ 0.50 mg kg −1 for the DTPA and AB‐DTPA methods and ≈ 2.0 mg kg −1 for the AAAc‐EDTA and Mehlich‐3 methods. These rates were well below the application rate of 30 mg Ni kg −1 of soil, in which Khalid and Tinsley (1980) observed depression of ryegrass shoot yield.…”

“…In spite of the fact that Ni has been officially recognized as an essential micronutrient for all higher plants since 2004, no efforts to determine its sufficiency critical levels with different soil tests have been reported in the literature, to the best of our knowledge. In our recent publication ( Nikoli and Matsi , 2014), 10 Ni soil tests were evaluated in cultivated soils. We concluded that, among the 10 soil tests for Ni, the most reliable tests were primarily the AAAc‐EDTA (acid ammonium acetate‐ethylenediaminetetraacetic acid disodium salt 2‐hydrate) and Mehlich‐3 methods and secondarily the AB‐DTPA (ammonium bicarbonate–diethylenetriaminepentaacetic acid) and DTPA (diethylenetriaminepentaacetic acid) methods.…”