Short-term effects of fertilization on dissolved organic matter (DOM) in soil leachate

Abstract

Abstract. Besides the importance of dissolved organic matter (DOM) in soil biogeochemical processes, there is still a debate on how agricultural intensification affects the composition and concentration of dissolved organic matter leached from soils into adjacent aquatic ecosystems. In order to investigate the immediate response of DOM leaching to fertilization, we conducted a short-term (45 day) lysimeter experiment with undisturbed silt loam and loamy sand soil cores. Mineral (calcium ammonium nitrate) or organic (pig slurry) fertilizer was applied on the soil surface with a concentration equivalent to 130 kg N ha−1. After fertilization, soil leachate was collected in 6-days intervals. Dissolved organic carbon concentrations (DOC) were measured with gas chromatography, while shifts in DOM composition were analysed using absorbance and excitation- emission fluorescence indices from peak-picking as well as from PARAFAC analysis. During the first 12 days, fertilization of a silt loam reduced DOC concentrations in the leachate and shifted its composition towards more microbial- like compounds. Additionally, the discrepancy in DOM composition between fertilizer and control treatments of a silt loam increased with time. However, in loamy sand only mineral fertilization affected organic matter leaching and decreased DOC concentrations in the leachate during the first 12 days. Furthermore, mineral fertilization of the loamy sand led to DOM compounds with low molecular size in the first 12 days. Our results show that fertilization tends to increase microbial transformed DOM, while it reduces leached DOC concentrations. Furthermore, the magnitude of fertilization on DOC concentrations and DOM composition was highly depending on the soil texture they originate from. However, in our set-up, the experimental soil units were restricted to a soil depth of 16 cm (Ap horizon). At ecosystem level, a sufficiently long soil passage might mitigate the impact of fertilization on soil DOM.

Influence of pH on the release of colloidal and dissolved organic matter from vertical flow constructed wetland surface sludge deposits

“…Between pH 7 and pH 12, for both samples, E2:E3 remains stable in the range of 4.5 to 3.5. These values were similar to those obtained for pore water of peatland that fluctuate around 4 [8,58] and for agricultural soil solution [59]. Finally, the evolution of SD characteristics with ageing seemed to affect only partially the molecular size of UVabsorbing leached organic molecules as shown by the similar E2:E3 between the two SDs.…”

Emerging investigator series: impacts of land use on dissolved organic matter quality in agricultural watersheds: a molecular perspective

“…Using Bruker DataAnalysis (v 4.4), baseline, background noise, and methanol/MilliQ subtractions and peaks below S/N ratios of 4 were excluded. DOM molecular formulae were determined within the elemental constraints: 12 C( 1-100 ), 1 H( 1-200 ), 16 O( 1-50 ), 14 N( 0-2 ), 32 S( 0-2 ) and 31 P( 0-2 ) with a mass tolerance of ±0.5 ppm. Isotopes of 13 C and 18 O were identied for C and O containing DOM molecules to ensure accurate formula assignment to molecules.…”

“…15 For example, fertilizer application and organic amendments can also affect the quality of DOM by leading to nitrogen-containing and proteinaceous DOM signatures associated with more eutrophic conditions in agriculture-draining streams. 16 The increase in urbanization and agricultural land usage has led to enhanced carbon export from soils through soil compaction, vegetation loss, and changes in hydrology. 11 Practices such as tilling or employing heavy machinery can also affect the structural integrity of soil, resulting in higher soil organic carbon inputs that ultimately reduce soil quality and organic carbon sequestration in soils.…”