Published online 1 May 2008
Published in Soil Sci Soc Am J 72:860 (2008)
DOI: 10.2136/sssaj2008.0035L
© 2008 Soil Science Society of America
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COMMENTS AND LETTERS TO THE EDITOR
Response to Comments on "Modeling Energy Inputs to Predict Pedogenic Environments Using Regional Environmental Databases"
Craig Rasmussen*
Dep. of Soil, Water and Environmental Science, The Univ. of Arizona, 1177 E. Fourth St., Shantz Bldg. Rm. 429, Tucson, AZ 85721-0038
* Corresponding author (crasmuss{at}ag.arizona.edu).
FIELD AND MINASNY point out the similarity between the pedogenic energy model described in Rasmussen et al. (2005) and Rasmussen and Tabor (2007) to an energy model formulated by Volobuyev (1964). We appreciate Field and Minasny bringing the work of Volobuyev to our attention as we were not familiar with this work and therefore it was not considered in our review and discussion of pedogenic energy models. Upon review of Volobuyev (1964) and the other publications noted in the Field and Minasny comment (Volobuyev, 1974; 1983; 1984; 1985), we concur that indeed there is much similarity between the conceptual and mathematical constructs of the respective energy models; however there are differences between the two constructs and the comparison of Field and Minasny that should be noted and clarified.
The Volobuyev construct is framed around what was termed an "energy balance of soil formation." As stated in Volobuyev (1964) and summarized by Field and Minasny, this energy balance represents a measure of energy participating in soil formation based on a summation of energy expenditures, with particular quantitative focus on climatic, biologic and mineral weathering parameters. The climatic parameters are quantified as the total energy expended as evaporation and transpiration, with values for this parameter estimated to near 2800 MJ m–2 yr–1 for humid tropical systems. This model does not include a direct climatic energy term quantifying energy input related to effective precipitation, that is, precipitation water in excess of evapotranspiration. Rather effective precipitation is used to estimate mineral weathering (noted below). The biologic parameter is quantified from an empirical estimate of biomass production and the amount of solar energy converted to simple sugars via photosynthesis, with values estimated up to 125 MJ m–2 yr–1 for humid tropical systems. The mineral weathering energy parameter is estimated according the amount and temperature of water participating in a simple weathering reaction (i.e., the water mediated transformation of feldspar to gibbsite), with values ranging from zero up to 630 kJ m–2 yr–1 for desert and humid tropical systems, respectively. The amount of water available to react is estimated from effective precipitation (termed Pk by Volobuyev). The values for evapotranspiration, biologic production and mineral weathering are then summed as an estimate of the energy expended during soil formation. Stated in this form, the energy model of Volobuyev represents a general accounting of energy expenditures rather than an energy balance per se.
The quantitative pedogenic energy model (QPEM) presented in Rasmussen et al. (2005) and Rasmussen and Tabor (2007) uses an estimated rate of effective energy and mass transfer (EEMT) to the soil system from precipitation (EPPT) and biologic production (ENPP) as an estimate of pedogenic environment and energy available to do work within the soil system. The two QPEM energy terms are derived directly from the amount and timing of effective precipitation using a simple monthly water budget (Arkley, 1963) to account of seasonality. The EPPT term characterizes the amount of water available to drive both biotic and abiotic reactions, similar in concept to the use of Pk and temperature to estimate the energy expenditure of mineral transformation by Volobuyev. As noted by Field and Minasny, the ENPP term is very similar to the biologic energy component of Volobuyev, and indeed much ecological literature characterizes biologic production in energy terms (e.g., Odum, 1987). The ENPP term is estimated based on the timing of effective precipitation, with values ranging up to 58 MJ m–2 yr–1 for humid tropical systems, roughly half that estimated by Volobuyev (1964). This is to be expected though, as the Volobuyev biologic term represents a gross primary production rather than a net primary production.
The sum of the two QPEM energy terms (noted as EEMT) represents an input of energy available to do work within the soil system, for example, energy available to drive mineral weathering or organic matter cycling, and does not include energy cycled through evapotranspiration as in the Volobuyev accounting. Evapotranspiration by far represents the largest energy component of the Volobuyev model and clearly explains the order of magnitude discrepancy in energy between the QPEM and Volobuyev models noted by Field and Minasny. In contrast to the general summation and accounting of the Volobuyev model, the QPEM framework may be stated as an actual energy balance: QIN = 
S + QOUT, where EEMT is equivalent to QIN, S the change in energy storage within the soil system, and QOUT the energy exported from the soil system.
We again thank Field and Minasny for bringing the Volobuyev energy model to our attention. This work indeed deserves to be included in the discussion and derivation of energy based pedogenic models.
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Received for publication February 4, 2008.
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REFERENCES
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- Arkley, R.J. 1963. Calculation of carbonate and water movement in soil from climate data. Soil Sci.
96
:239–248.
- Odum, H.T. 1987. Self-organization, transformity, and information. Science
242
:1132–1139.[CrossRef][Web of Science]
- Rasmussen, C., R.J. Southard, and W.R. Horwath. 2005. Modeling energy inputs to predict pedogenic environments using regional environmental datasets. Soil Sci. Soc. Am. J.
69
:1266–1274.[Abstract/Free Full Text]
- Rasmussen, C., and N. Tabor. 2007. Application of a quantitative pedogenic energy model to predict soil development across a range of environmental gradients. Soil Sci. Soc. Am. J.
71
:1719–1729.[Abstract/Free Full Text]
- Volobuyev, V.R. 1964. Ecology of Soils. Academy of Sciences of the Azerbaidzn SSR. Institute of Soil Science and Agrochemistry. Israel Program for Scientific Translations, Jerusalem.
- Volobuyev, V.R. 1974. Main concepts of soil ecology. Geoderma
12
:27–33.[CrossRef][Web of Science]
- Volobuyev, V.R. 1983. Thermodynamic basis of soil classification. Soviet Soil Sci.
15
:71–83.
- Volobuyev, V.R. 1984. Two key solutions of the energetics of soil formation. Soviet Soil Sci.
16
:1–8.
- Volobuyev, V.R. 1985. Biological component energetics of soil formation. Soviet Soil Sci.
17
:1–4.
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