Mean residence times and characteristics of humic substances extracted from a Taiwan soil

Abstract

Humic substances are well known for their long-term persistence in soil environments. The relationship between the mean residence times (MRT) and characteristics of humic substances extracted from a soil with highorganic matter (OM) content in Taiwan was investigated. The MRTs of the soil organic matter (SOM) and its humic substances extracted from the soil samples taken from three depths (0–20, 40–60, and 70–150 cm) of a soil profile were determined by 14C-dating procedures. Moreover, the humic substances were subjected to elemental analysis and investigation by electron spin resonance (ESR), Fourier transform infrared (FTIR), and solid-state 13C nuclear magnetic resonance (13C NMR) spectroscopies. The ranges of the MRT of fulvic acids (FA) (MW < 1000), FA (MW > 1000), humic acid (HA) (MW > 1000), and humins (MW > 1000) were 143 ± 110 to 1740 ± 60, 213 ± 120 to 1690 ± 200, 253 ± 60 to 2200 ± 40, and 293 ± 40 to 2173 ± 70 yr, respectively. The higher standard deviations of the means of determined MRTs of FA (MW < 1000) and FAs (MW > 1000) may be due to their lability. Further, the MRTs of the FAs (MW < 1000), FAs (MW > 1000), HAs (MW > 1000), and humins (MW > 1000) increased with increasing soil profile depth, indicating the slow biological and chemical degradations of humic substances in the deeper layers. The elemental composition and spectroscopic properties of FTIR, 13C NMR, and ESR of humic substances did not change significantly with their MRTs. The MRTs in the range observed in this study were apparently long enough to render humic substances a high degree of chemical stability. Key words: Humic substances, mean residence times, ESR, FTIR, 13C NMR, humin

Characterization of Humic Substances Derived from Swine Manure-Based Compost and Correlation of Their Characteristics with Reactivities with Heavy Metals

“…This indicates that the yield of HA (MW > 1000) was substantially higher than those of FA (MW > 1000) and FA (MW < 1000), becoming the major component of organic matter of the swine manure-based compost. The C, H, N, O, and S contents of the extracted humic substances are presented in Table 2, and these results indicate that C, H, N, O, and S contents of the extracted humic substances extracted from the swine manure-based compost are close to those of natural humic substances derived from soils and waters (22,28,31). Chang Chien et al (32) studied the fertilizer effect (including swine manure-based compost and this compost complemented with various chemical fertilizer nitrogen rates) applied to a paddy-upland rotation on characteristics of HAs (MW > 1000).…”

Linking Phosphorus Sequestration to Carbon Humification in Wetland Soils by 31P and 13C NMR Spectroscopy

“…Carbon compounds in plant tissue degrade at markedly different rates, so information on soil organic carbon structure can provide important clues about organic matter decomposition or stabilization in soils. For example, most plant derived carbohydrates are readily degraded, whereas more refractory compounds become stabilized and may persist in the soil for thousands of years . Linking phosphorus speciation and soil organic carbon composition is, therefore, a key aspect of any effort to understand soil phosphorus stabilization …”

“…For example, most plant derived carbohydrates are readily degraded, 8 whereas more refractory compounds become stabilized and may persist in the soil for thousands of years. 9 Linking phosphorus speciation and soil organic carbon composition is, therefore, a key aspect of any effort to understand soil phosphorus stabilization. 10 Assessment of soil phosphorus chemistry often begins by partitioning phosphorus into labile and refractory components, especially to index phosphorus availability for plant growth.…”

Soil organic matter biochemistry and potential susceptibility to climatic change across the forest‐tundra ecotone in the Fennoscandian mountains

“…This will exert a strong control on potential CO 2 release under conditions more favourable for microbial activity (Sjöberg, 2000 (PhD thesis)). For example, most plant‐derived carbohydrates are readily degraded in soils (Hopkins et al ., 1997), whereas more recalcitrant compounds become stabilised and may persist in the soil for many thousands of years (Wang & Chang, 2001). Chemical information is currently limited for high latitude soils, but detailed information can be obtained using solid‐state 13 C nuclear magnetic resonance with cross‐polarisation magic angle spinning (CPMAS 13 C NMR), which has proved a powerful tool in studying the composition and decomposition of SOM (Baldock et al ., 1990; Nordén & Berg, 1990; Baldock & Preston, 1995; Kinchesh et al ., 1995; Preston, 1996; Baldock et al ., 1997; Condron & Newman, 1998; Kögel‐Knabner, 2000; Sjöberg, 2000 (PhD thesis); Kögel‐Knabner, 2002).…”