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.