Assessment of nutrients and salt contaminants in the soil and
foliage
The concentration of nutrients and contaminants in the harvested soil
and foliage samples was measured at the Laboratory of Plant Mineral
Nutrition in Latvia. In the case of soil samples and for a majority of
elements (N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, Mo, B, Na), the air-dried
and 2 mm-sieved soil samples were extracted using 1:5 (v/v) soil:1 M HCl
extracting mixtures for 1 hour (Osvalde, 2011). P, S and Mo were
separated from other elements by oxidizing 100 ml extracts with hot
conc. HNO3, H2O2 and
HClO4 and dissolving the retrieved salts in diluted HCl
(Rinkis et al., 1987). The concentration of Ca, Mg, Fe, Cu Zn and Mn was
determined by means of atomic absorption spectroscopy, using an
acetylene-air flame atomizer (Perkin Elmer Aanalyst 700; Rinkis et al.,
1987; Motsara & Roy, 2008). That of P, Mo, N, and B was estimated by
colorimetry, using molybdenum blue in acid-reduced medium (P),
thiocyanate in acid-reduced medium (Mo), Nessler’s reagent in alkaline
medium after modified Kjeldal digestion (N), hinalizarine in sulfuric
acid medium (B), whereas S was measured by turbidimetry after adding
BaCl2, using a JENWAY 6300 spectrophotometer (Barloworld
Scientific Ltd., Gransmore Green Felstad, Dunmow, Essex, UK). The
concentration of K and Na was measured by flame photometry using a
JENWAY PFPJ photometer (Jenway Ltd, Gransmore Green, Felsted Dunmow,
Essex, UK). Estimates of Cl were obtained by AgNO3titration after distilled water extraction All analyses were performed
in triplicates.
For estimates of mineral nutrients and contaminants in the foliage of
lime trees, the harvested leaf samples were washed in distilled water,
dried 24 hours at +60 oC, and ground to powder using a
laboratory mill (IKA, A11 basic, Germany). Nutrients and contaminants
were extracted by dry-ashing the milled samples using concentrated
HNO3 vapors and dissolving the mineral fraction in
either 3% HCl (P, K, Ca, Mg, Fe, Mn, Zn, Cu, Mo, B, Na) or distilled
water (Cl). In the case of N and S, the milled samples were wet-digested
in either conc. H2SO4 (N; modified
Kjeldahl method) or conc. HNO3 and HClO4(S). All elements were analyzed using the same procedures as in the case
of soil samples.