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.
Highlights
Soil organic matter (SOM), which is usually estimated by total organic C content, can be understood as the collection of organic substances and complexes present in the soil (Silva and Mendonça, 2007)
Before the excessive volume of residues generated by Embrapa and Walkley-Black methods, for alignment with green chemistry principles, pre-tests were conducted by reducing the soil mass from 0.5 to 0.2 g
Since K2Cr2O7 must be present in a stoichiometric relationship with analytes, and H2SO4 is responsible for the energy release per milliliter of solution and access to organic C (APHA, 1995), these reagents have been proportionally reduced with mass reduction
Summary
Soil organic matter (SOM), which is usually estimated by total organic C content, can be understood as the collection of organic substances and complexes present in the soil (Silva and Mendonça, 2007). Elemental analysis, which is a process based on combustion of the sample followed by chromatographic separation and detection of gases formed, despite being a clearer alternative and operational for the analysis of the organic C present in SOM (Ma, 2001; Harris, 2005), presents the inconvenience of adding to this inorganic C (carbonate), and is a technique that is not yet feasible for most Brazilian soil fertility laboratories. This is due to the initial and routine high cost investment of this technique. Even the Interlaboratory Program of Fertility Laboratories Quality Assessment (PAQLF, 2014), coordinated by the National Center of Soil Research (CNPS), currently called Embrapa Soils, adopts as standard the moist method of Embrapa (Silva, 2010)
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