Selenium speciation and extractability in Dutch agricultural soils

Area of Science:

• Environmental Chemistry
• Soil Science
• Agricultural Science

Background:

• Selenium (Se) is an essential trace element, but its speciation and bioavailability in agricultural soils are complex.
• Understanding Se speciation is crucial for assessing soil health and potential plant uptake in agricultural systems.

Purpose of the Study:

• To investigate selenium speciation and extractability in Dutch agricultural soils.
• To determine the dominant forms of selenium and their relationship with soil organic matter.

Main Methods:

• Analysis of topsoil samples from 42 grassland and 41 arable fields in the Netherlands.
• Quantification of total Se using aqua regia digestion.
• Speciation analysis using sequential extraction techniques including NaOCl, ammonium oxalate, and NaOH extractions, coupled with HPLC-ICP-MS.

Main Results:

• Organic Se constituted, on average, 82% of total Se, while inorganic selenite accounted for about 5%.
• Selenium extractability generally followed the order of aqua regia > NaOCl > NaOH > ammonium oxalate > hot water > HNO3 > CaCl2.
• Strong positive correlations were observed between total Se and soil organic matter content, indicating Se association with organic fractions.

Conclusions:

• Dutch agricultural soils are dominated by organic selenium forms.
• Selenium extractability is largely governed by soil organic carbon, but variations in Se:C ratios suggest changes in organic matter composition.
• Further research into specific organic Se fractions and their bioavailability is warranted.