Characterization by Fluorescence of Organic Matter from Oxisols under Sewage Sludge Applications

Abstract

Sewage sludge from wastewater treatment contains organic matter and plant nutrients that can play an important role in agricultural production and the maintenance of soil fertility. The present study has aimed to evaluate the degree of humification following sewage sludge application of soil organic matter by laser‐induced fluorescence and humic acids using ultraviolet‐visible fluorescence, and including comparison with Fourier‐transform infrared spectroscopy and elemental analysis. Sewage sludge applications to the soil caused a decrease in the degree of humification of the soil organic matter and humic acids for both a Typic Eutrorthox (clayey) soil and a Typic Haplorthox (sandy) soil of around 14 and 27%, respectively. This effect is probably due to incorporation of newly formed humic substances from the sewage sludge into the characteristics of less humified material, and to the indigenous soil humic substances. The minor alterations observed in the clay soil probably occurred due to both the greater mineral association, which better stabilized the indigenous soil organic matter, and the higher microbial activity in this soil, which accelerated sewage sludge mineralization. Sewage sludge applications increased the C content for the clay and sandy soils by 7.4 and 15.4 g kg−1, respectively, suggesting a positive effect on these two soils.

Chemical and Biochemical Properties of Oxisols after Sewage Sludge Application for 16 Years

“…Only at high applications, above 75 Mg ha -1 , the effect of SS on OM contents stayed longer (Santos et al, 2010). This information is important because it reinforces SS as an alternative to enhance OM levels, especially in OM poor soils.…”

“…In contrast, FDA had a very low variation coefficient (17.3 %), as well as variability among treatments. It is noteworthy that FDA hydrolysis does not express a specific enzyme activity, but the activity of a whole group of enzymes including lipases, esterases and proteases (Melo et al, 2010). Fluorescein diacetate can be hydrolysed by algae, protozoa and animal tissues, so that SS was not favorable to them.…”

“…Soil samples were incubated with and without triphenyl tetrazolium chloride (TTC) at 30 °C for 24 h, and followed by quantification of triphenyl formazan (TPF) by spectrophotometry to determine dehydrogenase activity (Melo et al, 2010).…”

“…The potential of the fluorescein diacetate hydrolysis (FDA) was assessed by soil sample incubation with and without FDA, evaluating the content of fluorescein produced (Melo et al, 2010).…”

Origin, concentration, availability and fate of dissolved organic carbon in coastal lagoons of the Rio de Janeiro State

“…Also, these three lagoons presented higher fluorescence emission concentrated in the right upper quadrant, spreading toward the right upper corner (Figure 3a, b, and c). This indicates that humic DOC in these systems is similarly highly aromatic, which is a result of the continued humification process (Santos et al, 2010). This pattern is reinforced by the humification index (sensu Zsolnay et al, 1999), which presented relatively high and quite similar values to AmarraBoi, Atoleiro and Comprida lagoons (Figure 3a, b and c).…”