This is a fast, simple procedure for determining B in soil extracts when an ICPAES is available, especially when large sample numbers are involved (Zarcinas and Cartwright 1983). After filtration, no further sample preparation is necessary before analysis by ICPAES. When readings are carried out at 208.9 nm, no interferences occur at elemental levels normally encountered in soil extracts. If the more sensitive B emission wavelength of 249.8 nm is used, corrections must be made for spectral enhancement due to Fe. Other details of this empirical soil B method are given in the preamble to method 12C1.
Across 72 air-dry and finely ground soils used in ASPAC interlaboratory proficiency programs from 1997–2007 (e.g. Peverill and Johnstone 1997; Rayment et al. 2007), the grand median robust % CV for this test was 38% at a grand median concentration of 0.79 mg B/kg. Across the same period, there was no apparent continuous relationship between concentrations and robust % CVs.
0.01 M Calcium Chloride Extracting Solution
As for Method 12C1.
Boron Primary Standard
As for Method 12C1.
Boron Secondary Standard
As for Method 12C1.
Boron Working Standards
Pipette 2.5, 5, 10, 15, 20, 30, 40 and 50 mL B Secondary Standard into separate 500 mL volumetric flasks. Dilute to volume with 0.01 M CaCl2 Extracting Solution. These solutions contain 0.1–2.0 mg B/L. For a 1:2 soil/solution ratio, these standards contain concentrations of B equivalent to 0.2, 0.4, 0.8, 1.2, 1.6, 2.4, 3.2 and 4.0 mg B/kg of soil.
Obtain clarified extracts as described in Method 12C1. Cool, then determine B concentrations from appropriate working standards using ICPAES.
Follow manufacturer’s instructions for instrument calibrations; the preferred wavelength is 208.9 nm for reasons given by Jeffrey and McCallum (1988).
Report CaCl2-extractable B (mg B/kg) on an air-dry basis.