Development of Alternative Methods for Determining Soil Organic Matter

Abstract

Soil organic matter (SOM) is important to fertility, since it performs several functions such as cycling, water and nutrient retention and soil aggregation, in addition to being an energy requirement for biological activity. This study proposes new trends to the Embrapa, Walkley-Black, and Mebius methods that allowed the determination of SOM by spectrophotometry, increasing functionality. The mass of 500 mg was reduced to 200 mg, generating a mean of 60 % saving of reagents and a decrease of 91 % in the volume of residue generated for the three methods without compromising accuracy and precision. We were able to optimize conditions for the Mebius method and establish the digestion time of maximum recovery of SOM by factorial design and response surface. The methods were validated by the estimate of figures of merits. Between the methods investigated, the optimized Mebius method was best suited for determining SOM, showing near 100 % recovery.

Evaluation of a microplate spectrophotometer for soil organic carbon determination in south‐central Idaho

“…However, the quantification of reduced chromium is made through ultraviolet-visible light absorbance using a spectrophotometer. The present study followed the procedure of Souza et al, (2016) with a minor increase in soil volume as SOC tends to be low in soils of south central Idaho. A brief description of the method follows.…”

“…The color of each sample is related to organic C through a standard curve generated by adding increasing amounts of ferrous ammonium sulfate to reduce dichromate in standard flasks treated otherwise identically to unknowns (S2). This method of SOC determination is also subject to incomplete oxidation of SOC (Souza et al, 2016); therefore, the standard correction factor of 1.33 was applied.…”

“…Loss on ignition at 360°C LOI 360°C Storer, 1984;Miller et al, 2013 Walkley-Black titrimetric variant WBTIT Walkley and Black, 1934 Walkley-Black spectrophotometric variant WBSPEC Walkley and Black, 1934;Souza et al, 2016 Dry combustion w/o pretreatment -Pressure calcimeter DC w/o pretreatment -Pcal Wagner et al, 1998;Sherrod et al, 2002 Table 4. Bland-Altman estimates of fixed bias for all soils, n=85, and the lower 75 th percentile of soil organic carbon content determined by the Walkley-Black titration (<13.11 g kg -1 ) for soils of south central Idaho, n=56.…”

Chemical Speciation and Mobility of Heavy Metals in Soils Around Nasara Sack and Packaging Company Akwanga, Nigeria

“…Soil organic carbon was determined by oxidation using potassium dichromate and concentrated sulphuric acid. Considering that the average content of carbon in soil organic matter is equal to 58 % the conversion factor 1.724 was used to calculate the percentage of organic matter from the content of organic carbon [8,9]. Nitrogen content of the soil was determined using method describe by Kjeldahl [10] while the phosphorus content using molybdate reagent by means of spectrophotometer set at wavelength of 660 nm then the cation exchange capacity was estimated using the Bray and Kurtz Hydrometer method [7,11].…”

Optimization of the analytical method for the determination of organic matter

“…In clay rich soils it enables the formation of aggregates with large pores and improves therefore water and air availability. Besides being essential in soil studies, the soil organic matter parameter is the most important one in several soil properties such as structure, coloring, water retention, and cation exchange capacity; as a result it becomes important in guiding soil fertilizing and irrigation (Souza et al, 2016).…”