Turnover of Soil Organic Matter

Appropriate tracers to investigate SOM turnover rates are C and C, the two naturally occurring isotopes of C. The radioactive C atom is cojitinuously formed in the atmosphere by solar radiation and from the remaining C in organic compounds their age can be estimated. The mean natural abundance of C is constant however, small variations in the C/ C ratio identify sources and processes involved in the formation of organic molecules. The best-known examples are the isotopic difference between heavy C4 plants and light C, plants and the isotopic enrichment of food chains. 

FIGURE 14 Elemental and molecular characteristics of different particle-size fractions of soil organic matter and size relation to organic matter. 

Additionally, the C signal, introduced by atmospheric thermonuclear bomb tests at the end of the 60s, can be used to investigate turnover rates of SOM. This signal is often found in the upper 

Carbon turnover rates can be estimated using natural labeling techniques with C in combination with vegetation shifts from light C, plants to heavy C, plants. (Balesdent and Guillet, 

Coarse particles that are mainly fresh litter have mean residence times between 0.5 and 20 years, whereas the carbon in the clay fraction has mean residence times of about 60-80 years (Balesdent, 1996). Recently, the direct determination of molecular turnover rates using pyrolysis products was applied to SOM after vegetation change (Gleixner et al, 1999). This technique indicated mean residence times between 9 and 220 years for individual pyrolysis products for the first time. Most intriguing was the fact that 

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Skjemstad JO, Le Feuvr RP, Prebble RE (1990) Turnover of soil organic matter under pasture as determined by 13C natural abundance. Aust J Soil Res 28 267-276... 

Grayston SJ, Vaughan D, Jones D (1996) Rhizosphere carbon flow in trees, in comparison with annual plants the importance of root exudation and its impact on microbial activity and nutrient availability. Appl Soil Ecol 5 29-56 Gregorich EG, Ellert BH, Monreal CM (1995) Turnover of soil organic matter and storage of com residue carbon estimated from natural 13C abundance. Can J Soil Sci 75 161-167... 

O Brien, B. J., and Stout, J. D. (1978). Movement and turnover of soil organic matter as indicated by carbon isotope measurements. Soil Biol. Biochem. 10, 309-317. 

Jenkinson, D. S., and Rayner, J. H. (1977). The turnover of soil organic matter in some of the Rothamsted classical experiments. Soil Sci. 123, 298-305. 

These changes in soil C stocks are relatively rapid, due to rapid turnover of soil organic matter (SOM) in these tropical soils. Using radiocarbon derived from atmospheric testing of nuclear weapons in the 1960s as a tracer, Trumbore et al. (1995) estimated that the mean residence time of C in the top 10 cm of soil is about 3 years for 30% of the SOM and 10-30 years for 60% of the SOM. Only about 10% of the C in the top 10 cm of soil cycles on a millennial time scale. This very old C fraction increases to 40-80% in the... 

GUILLET B. 1982. Studies of the turnover of soil organic matter using radio-isotopes (14-c). In Constituents and Properties of Soils. Eds. Bonneau M. and Souchier B. Academic Press, London. 

NANNIPIERI P. and SEQUI P. 1982. Soil Fertility - the determination and the turnover of soil organic matter. In Evolution du niveau... 

The distribution of SOC with depth is attributed mainly to continuous input and decomposition of soil organic matter (SOM), and correlates directly with soil development and SOM turnover (Chen et al. 2005). Regional, continental or global models are useful to understand SOM dynamics according to land use changes and management practices (Cole et al. 

Agren GI, Bosatta E, Balesdent J (1996) Isotope discrimination during decomposition of organic matter a theoretical analysis. Soil Sci Soc Am J 60 1121-1126 Balesdent J (1987) The turnover of soil organic fractions estimated by radiocarbon dating. Sci Total Environ 62 405-408... 

Baisden WT, Amundson R, Brenner DL, Cook AC, Kendall C, Harden JW (2002) A multi-isotope C and N modeling analysis of soil organic matter turnover and transport as a function of soil depth in a California annual grassland soil chronosequence. Global Biogeochem Cycles 16 1135. doi 10.1029/2001GB001823... 

Balesdent J, Mariotti A (1996) Measurement of soil organic matter turnover using 13C natural abundance. In Boutton TW, Yamasaki S (eds) Mass spectrometry of soils. Marcel Dekker Inc., New York, pp 83-112... 

Coleman K, Jenkinson DS (1996) RothC-26.3 a model for the turnover of carbon in soil. In Powlson DS, Smith P, smith PJU (eds) Evaluation of soil organic matter models using existing long-term datasets, vol 38. NATO ASI Series I, pp 237-246 Collins HP, Blevins RL, Bundy LG, Christenson DR, Dick WA, Huggins DR, Paul EA (1999) Soil carbon dynamics in corn-based agroecosystems results from carbon-13 natural abundance. Soil Sci Soc Am J 63 584-591... 

Turnover Time and Dynamics of Soil Organic Matter 230... 

Historically, attention on soil organic matter (SOM) has focused on the central role that it plays in ecosystem fertility and soil properties, but in the past two decades the role of soil organic carbon in moderating atmospheric C02 concentrations has emerged as a critical research area.This chapter will focus on the storage and turnover of natural organic matter in soil (SOM), in the context of the global carbon cycle. 

TURNOVER TIME AND DYNAMICS OF SOIL ORGANIC MATTER... 

Krull, E. S., Baldock, J. A., and Skjemstad, J. O. (2003). Importance of mechanisms and processes of the stabilisation of soil organic matter for modelling carbon turnover. Fund. Plant Biol. 30(2), 207-222. 

Martin, J.P. and Haider, K. (1986) Influence of mineral colloids on turnover rates of soil organic matter. In Interactions of Soil Minerals with Natural Organics and Microbes, (Huang, P.M., and Schnitzer, M., eds.), pp. 283-304, Soil Science Society of American Special Publication, Madison. 

Balesdent J. and Mariotti A. (1996) Measurement of soil organic matter turnover using C natural abundance. In Mass Spectrometry of Soils (eds. T. W. Boutton and S. 1. Yamasaki). Dekker. 

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