A new method was proposed that complements the value of active carbon in the soil expressed as hot-water soluble carbon C hws . The method is based on vacuum measurements of biochemical oxygen demand (BOD) of soil suspensions using an Oxi Top Control system manufactured by the WTW Merck Company that is destined for hydrochemical analyses of organically contaminated waters. Measurements will provide BOD values for particular days of incubation; total limit BOD t can be determined from these values, and it is possible to calculate the rate constant k 1 of mineralization of a decomposable part of soil organic matter. It is typical of soil organic matter (SOM) of a given soil sample and comparable with the BOD 5 :COD (chemical oxygen demand) ratio that is used to evaluate degradability of water organic contamination in hydrochemical analytics.Keywords: soil organic matter (SOM); decomposable part of SOM; mineralization kinetics; analytical method Soil organic matter (SOM) undergoes short-and longterm transformations in the soil. Long-term transformations last for tens of years and establish a new dynamic equilibrium. The amount of long-time unchangeable inert soil organic matter can be determined from unfertilized parcels of long-term trials. There exists a relation between the content of fine particles in soil (below 6.3 µm) and the amount of carbon in inert soil organic matter (Körschens 1980). A difference between total content of C org in farmed soils and the calculated content of inert carbon is considered as carbon of decomposable organic matters C dec . Under a dynamic equilibrium a portion of SOM is mineralized during one growing season, and the same portion is newly formed. This portion of soil organic matter is considered as active and its carbon is active organic carbon. To determine the active carbon the easiest and most suitable method is determination of so called hot water extractable C hws (Körschens et al. 1990, Schulz 1990, Weigel et al. 1998). Carbon C dec of decomposable organic matters was studied by Kubát and Vrzáková (1984), Kubát and Veselý (1986). Schulz (1997) expressed the relation between decomposable C dec and C hws by the equation C dec = 15C hws . C dec and/or C hws are important as energy substrates for soil microorganisms and material for mineralization, therefore they belong to the main traits of soil productivity. Optimum value of C hws in basic types and textures of soils is 0.3-0.6 g/kg, i.e. 0.03-0.06%.Through their enzymes soil microorganisms are able to mineralize less soluble carbon sources while the rate of this process is different. In the present paper we tried to determine C dec of decomposable organic matters more exactly employing reaction kinetics of their mineralization.For this purpose we used biochemical oxygen demand (BOD), a current method of hydrochemical analytics for determination of organic contamination; it is regularly carried out as five-day incubation (Czech designation is BSK and BSK 5 ) or as BOD t (BSK c ) -i.e. the limit value of total biochemi...
We proposed a new method to determine the rate constant of biochemical oxidation of soil organic ma�ers that makes it possible to evaluate their stability by Spectroquant Merck BOD photometric tests; if smaller samplings are used and individual determinations are performed, it can replace the method of BOD vacuum measuring by an Oxi Top Control Merck system. The time and labour consumption of this vacuum method is sometimes criticised, but it has demonstrable work advantages for a large series of samples and so it is still recommended. The two methods are identical as for the correctness and coincidence of results and they do not differ by either lower or higher results and therefore we recommend the new method with photometric tests for smaller series of samples. For the high time and labour consumption we must warn against the use of traditional BOD dilution method with volumetric determination of oxygen for the determination of rate constants. MATERIAL AND METHODSTwo collection-testing samples of soils were used for the determinations: one sample with a higher content of organic matters, the other with a lower content and higher stability of these matters. These two different samples were analysed by a newly proposed method of photometric tests Spectroquant Merck BOD KT with the range of 0.5-3000 mg O 2 /l (cat. no. 100687) that is based on a modification of the traditional Winkler's method. We employed BOD standard for the preparation of 10 l of standard solution (cat. no. 100718) and BOD nutrient mixture with allylthiourea for 12 l of nutrient solution (cat. no. 100688). For each determination at least 4 oxygen reaction vessels for BOD determination (cat. no. 114663) were necessary. CHOD test with the range of 10-150 or 15-300 mg O 2 /l (cat. nos. 114540 and 114895) was used to determine the total amount of organic matters. These are cuvette, not reagent tests.Measurements were carried out in a Spectroquant NOVA 60 photometer that works with 12 filters by the diode field technique (reference ray technique), is connected to a PC with the software Windows Multi Achat II for data processing and has the memory capacity for 1000 data blocks. It has an Auto Select function for differentiation of tests according to the bar code and AQA (Analytical Quality Assurance) function.The two tested samples of the soils were analysed by the previously described method OXI Top Control WTW Merck .The procedure of sample preparation and the conduct of the cultivation process were the same as described in the cited paper. Because the photometric measurements are not accessible if the sample turns turbid, just before the photometric measurement the sample was drawn with a syringe and before the transfer into the cuvette of the apparatus it was filtered under an N 2 screen using an Anotop MERCK membrane filter of porosity 0.45 µm directly onto the perpendicularly upwards set syringe until air bubbles were removed from the filter. The spectrophotometer has a built-in function of "turbidity correction".The correctness of t...
Two methods developed by Prof. Dohányos and Doc. Zábranská from ICT in Prague (A) and Oxi Top Control AN 12 measuring system manufactured by MERCK Company (B), were used to determine the maximum yield of biogas and methane and the maximum rate of biogas and methane production per unit weight of biomass using buffered and macro- and micro-nutrient enriched grass biomass as a substrate. Statistical evaluation proved that the Oxi Top Control method did not provide significantly lower or higher results than the other method that is considered standard. Although the Oxi Top Control AN 12 method has a higher variance of measured values than the standard method, it can be recommended as a project and operation method for its work comfort and expeditiousness.
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