Optimizing soil dissolved organic matter extraction by grey relational analysis

Abstract

Dissolved organic matter (DOM) in soil plays an important role in the fate and transport of contaminants. It is typically composed of many compounds, but the effect of different extraction factors on the abundance of different DOM components is unknown. In this study, DOM was extracted from three soils (paddy field, vegetable field and forest soils) with various extraction time, liquid to solid ratios (LSRs), extractant types, and extractant concentrations. The LSR had a significant effect on DOM content, which increased by 0.5–4.0 times among the three soils when LSR increased from 2:1 to 10:1 (P < 0.05). Dissolved organic matter content increased by 4%–53% when extraction time increased from 10 to 300 min (P < 0.05). Extractant concentration had different effects on DOM content depending on the extractant. Higher concentrations of KCl promoted DOM extraction, while higher concentrations of KH2PO4 inhibited DOM extraction. Therefore, grey relational analysis was used to further quantitatively evaluate the effect of extraction time, LSR, and extractant concentration on DOM, using KCl as an extractant. For the paddy field and forest soils, the impact of these three factors on DOM extraction efficiency was in the following order: KCl concentration > LSR > extraction time. However, the effect was different for the vegetable field soil: LSR > extraction time > KCl concentration. Taking all these factors into account, 1.50 mol L−1 KCl and an LSR of 10:1 with a shaking time of 300 min was recommended as the most appropriate method for soil DOM extraction.