The distribution of native and labelled carbon between soil particle size fractions isolated from long‐term incubation experiments

Abstract

Four soils with 6, 12, 23 and 46% clay were fractionated according to particle size after incubation for 5-6 years with I4C labelled straw, hemicellulose or glucose: 6 2 3 % of the I4C was still present and the amount increased with increasing content of fine particles.Clay fractions contained 66-84% of the 14C and the silt fractions accounted for 4 1 9 % . <2% was found in the sand fractions and 4 9 % was water soluble. The distribution of the native C was: clay, 46-68%; silt, 2&31%; sand, 2-7%.The clay fractions had higher relative proportions of 14C than of native C, the reverse being true for the silt fractions. This distribution pattern was not directly related to soil clay content or to kind of organic amendment.The C enrichment factor of clay and silt fractions (per cent C in fraction/per cent C in whole soil) increased with decreasing fraction size for both native and 14C. However, clay enrichment factors were higher for I4C than for native C, whereas silt enrichment factors were lower.A soil (9% clay) that had been incubated in the field for 18 years with 14C labelled straw was also analysed. Labelled C content at sampling was 9% of the initial value. In contrast to the other soils the distribution of labelled and native C was similar in the clay and silt fractions, which contained 55% and 33% of the whole soil C, respectively.The results indicate that clay-bound organic matter may be important in mediumterm organic matter turnover, whereas silt-bound organic matter may participate in longer-term organic matter cycling.

Fractionation and Long‐Term Laboratory Incubation to Measure Soil Organic Matter Dynamics

“…The clay fraction had the narrowest C/N ratio (6.3-10.2). Christensen and Sorensen (1985) incubated soils for 5 yr with 15 N-NH 4 and 14 C-hemicellulose and found that the C/N ratio of labeled, organic C associated with clay was lower and that associated with silt was higher than that of the whole soils. The Hoytville soil had the highest clay content (50%) and this clay had the narrowest C/N ratio (6.3-6.7).…”

Fate of straw- and root-derived carbon in a Swedish agricultural soil

“…Over both sampling dates and all treatments, we found 87.6% of the total SOC stock in the silt and clay fraction, which is in line with results reported by Flessa et al (2008), who found 88% of the total SOC in this fraction in two German agricultural soils. Christensen and Sorensen (1985) also found 50-75% of SOC to be present in clay-sized separates, while silt accounted for another 20-40%. This highlights the importance of organo-mineral interactions, as well as silt-sized microaggregates, for SOC stabilisation (Ladd et al 1996;Christensen 1987;An et al 2015;Moreno-Cornejo et al 2015).…”

“…In a mechanistic perspective, four major mechanisms may explain the stability of SOM in soil: (i) spatial inaccessibility of SOM to decomposers due to aggregation, (ii) recalcitrance due to the chemical structure, (iii) stabilisation of SOM by interaction with mineral surfaces and (iv) energetical limitation microbes to decompose organic matter (Mueller et al 2014;von Lützow et al 2006;Fontaine et al 2007). The distribution of organic matter between soil size fractions is affected differently when soil organic matter levels change due to cultivation, straw incorporation, addition of mineral fertiliser or animal manure (Christensen and Sorensen 1985;Christensen 1987;Gregorich et al 1995).…”

Índice de desagregação do solo baseado em energia ultra-sônica

“…Consiste em expressar a energia emitida pelo aparelho por unidade de volume de suspensão solo-água, sendo esse critério adotado em diversos trabalhos (Christensen & Sorensen, 1985;Christensen, 1985Christensen, , 1986Christensen, , 1987Gregorich et al, 1989;Fuller & Goh, 1992;Fuller et al, 1995;Eriksen et al, 1995).…”

“…Revisões de literatura sobre dispersão ultrasônica indicam que não há um método padrão em uso (Watson, 1971;Christensen, 1985). Numerosos fatores, como potência liberada pelo aparelho, tempo de sonificação, relação solo-água, especificações do equipamento, temperatura da suspensão, gás dissolvido e profundidade de inserção da haste do aparelho na suspensão, podem influir na eficiência da dispersão (Edwards & Bremner, 1967;Saly, 1967;North, 1976;Raine & So, 1994).…”