Browsing by Author "Genova N."
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Item Comparative study of soil test methods for determination of plant available potassium in Bulgarian arable soils(2021-01-01) Angelova L.; Genova N.; Stoyanova S.; Surleva O.; Nekov I.H.; Ilieva D.; Surleva A.This comparative study was aimed at estimating analytical behavior of methods for determination of plant available potassium applied to Bulgarian arable soils and to reveal the relationship between the amount of extractable K. Twenty-four samples from two traditional agricultural regions in Bulgaria were studied. Soil potassium was extracted by NH4OAc/HOAc pH 4.5 (AA), diluted double acid (Mehlich 1), CaCl2, BaCl2 and a modified acetate/lactate method (ALM) and determined by Flame AES. The factors influencing the methods accuracy were identified and uncertainty was estimated. The expanded uncertainty was (in mg K2O (100 g dry soil)-1): 0.10 (ALM), 0.64 (Mehlich 1), 0.17 (CaCl2) and 1.1 (AA). The study revealed that the factor which mainly influence the uncertainty of the applied analytical methods for plant available potassium in soil was the calibration of Flame AES determination. The obtained results showed that extractable potassium lowered in the following order KALM ≥ KAA > KMechlich1 > KBaCl2 > KCaCl2. Soil potassium extracted by ALM procedure correlated with AA, BaCl2-K, CaCl2 –K and Mehlich 1 - K at 0.05 level of significance. ALM extracted between 1.2 to 5.8 times more soil K than other methods did. The obtained results provided a base for further study on correlation between extractable K and soil fertility indices for particular soil types and climatic regions in Bulgaria.Item Contribution to the Molybdenum Blue Reaction and its Application in Soil Analysis(2022-01-01) Angelova L.; Genova N.; Pencheva G.; Statkova Y.; Yotova V.; Surleva A.This paper presents a study on the molybdenum blue reaction (MB) as a finishing detection step in soil analysis for quantification of plant available phosphorus. An ammonium acetate/calcium lactate reagent (pH= 4.2) was used for soil phosphorus extraction. The molybdenum blue color reaction using premixed Murphy-Riley reagent and ascorbic acid as a reductant was reinvestigated. UV-Vis characteristics of MB, optimal wavelength, reaction time and concentration of reductant were studied. The effect of ascorbic acid concentration and the reaction time on linearity, bias and uncertainty was discussed. The molybdenum blue reaction was found to obey Beer’s law in the targeted concentration range of 0.04 – 1.0 mg L-1 PO4 3--P. The linearity was proved by “lack-of-fit” test. The uncertainty budget was made and the uncertainty was estimated by modelling approach, as well as single laboratory and quality control approach. The recovery and the expanded uncertainty were found to be, respectively, (95.7 ± 8.7) % (P= 95%, n = 3) and 9.2 mg PO4 3--P /kg dry soil (k = 2). The results showed that the soil sample inhomogeneity and the repeatability of extraction process were the main factors which contribute to the uncertainty of measurement in soil analysis.