CENTURY model

W. J. Parton and P. E. Rasmussen, Long-term effects of residue management in wheat/fallow century model simulations. Soil Sci. Soc. Am. J. 5H.550 (1994). 

The Book of Alchemy teaches its readers how to penetrate the obscure symbolic language of the alchemists. . . understand how alchemical transformation can initiate a profound change of consciousness, claimed by practitioners to bring eventual union with the Divine. . . practice traditional meditations and exercises. . . prepare herbal alchemical elixirs to benefit the body. . . and discover how the alchemists search for purity can become a twenty-first- century model for spiritual development"... 

A tremendous amount of research has been devoted to quantifying and modeling transport processes in the vadose zone, with readily available scientific literature (journals and textbooks) extending over the last half century. Modeling is used to quantify the dynamic redistribution of chemicals along the near surface and deeper subsurface profile, which often also is subject to reactive chemical processes including sorption, dissolution or precipitation, and volatilization. 

Figure 40 The effect of (a) soil temperature and (b) soil water on decomposition in the Century model.

Figure 16. General struetnre of the Century model I Hall et al, 2000).

In order to estimate the uncertainties in a model s predictions (the ut in Eq. (21)) for consistency checking, one must have estimates of the uncertainties in the model s input parameters. In the 20th century, model input uncertainties... 

FIGURE 10 The relationships between evapotranspiration and net primary production as they emerge from the Century model, applied globally. The near-linear realtionship between evaporation and NPP, very similar to those observed In semi-arid lands, is an emergent property. The differences in slope between biomes are largely due to differences in the C N ratio of different plant functional types. Indicating that ecosystem composition has direct effects on biogeochemistry (Scholes et al., 1999). 

Gijsman, A. J., Oberson, A., Tiessen, H., and Frie.sen, D. K. (1996). Limited applicability of the CENTURY model to highly weathered tropical soils. Agronomy J. 88, 894-903. 

FIGURE 2 Carbon flows in the Century model (Parton et al., 1987). 

FIGURE 3 Potential mean soil carbon turnover rates extrapolated to the global scale using the temperature and soil texture relationships from the Century model (Schimel et al, 1994), See also color insert. 

FIGURE 3 Comparison between the observed seasonal cycle of COi and the simulated seasonal cycle produced by coupling the monthly estimates of net ecosystem production estimated by the Century model and fossil fuel emissions with the Hamburg ocean and atmospheric transport models for each of the seven high-latitude monitoring stations. The first six months of each cycle are displayed twice to reveal the annual variation more clearly. Mean and standard deviation are shown for the observed data (McGuire et iiL, 2000). 

Raich, J.W., Parton, W.J., Russell, A.E., Sanford, R.L. and Vitousek, P.M. (2000) Analysis of factors regulating ecosystem development on Mauna Loa using the Century model. Biogeochemistry 51, 151-191. 

The review of phosphorus models by Lewis and McCechan (2002) showed that one of the major differences in phosphorus cycling models is the number of inorganic and organic phosphorus pools and the ability to measure them in the laboratory. Models such as CENTURY have included phosphorus pools that are conceptually important for the model structure, but are difficult to measure. For example, the CENTURY model includes separate pools for parent phosphorus, strongly sorbed phosphate and occluded phosphorus, while... 

This chapter is an extension of the Raich et al. (2000) use of the CENTURY model to simulate carbon, nitrogen and phosphorus dynamics during soil development in Hawaii. 

The CENTURY model also includes a simplified water budget model that calculates monthly evaporation and transpiration water loss, water content of the soil layers, snow water content, and water flows between the soil layers. The main abiotic driver for the water budget model is the potential evapotranspiration rate, which is calculated as a function of the average monthly maximum and minimum air temperature. Near surface soil temperature is calculated as a function of maximum and minimum air temperatures, litter and standing plant biomass. The plant production model calculates potential plant production as a function of soil temperature and the ratio of actual water loss to potential water loss. Potential plant production is reduced when nutrients limit growth and the element that is most limiting for plant growth controls plant production. The nutrient... 

Fig. 15.3. Flow diagram for the phosphorus cycling subroutine in the CENTURY model. M = multiplier for effects of moisture and temperature L = lignin/N.

Fig. 15.5. CENTURY model-simulated patterns for soil organic nitrogen and phosphorus (a) and occluded phosphorus, parent phosphorus, non-occluded mineral phosphorus (labile plus sorbed phosphorus) and organic phosphorus (b) during 4.1 million years of soil development (0-50 cm soil depth). Observed data are plotted on the figure for organic nitrogen and phosphorus.

Fig. 15.6. CENTURY model-simulated results for soil phosphorus loss (organic and inorganic phosphorus) total nitrogen loss (nitrate, gaseous nitrogen and dissolved organic nitrogen) and nitrate loss (a) and change in live leaf carbon-to-nitrogen and carbon-to-phosphorus ratios (b) for the Hawaiian 4.1 million year soil chronosequence.

The CENTURY model simulates losses of nitrogen via gas fluxes (N2, N2O and NOJ, dissolved organic loss, and nitrate leaching loss, while phosphorus is lost via dissolved organic and inorganic phosphorus. Model results (Eig. 15.5b) show that total phosphorus loss is quite high during the first... 

Fig. 15.7. CENTURY model results for the impact of adding nitrogen and phosphorus fertilizer on tropical soils after 300 years (a), 2000 years (b), 20,000 years (c), 150,000 years (d), 250,000 years (e), and 1.4/4.1 million years (f) of soil development.

A central and long-standing conundrum of tropical biogeochemistry is the existence of high rates of terrestrial productivity on highly weathered soils that can fix large amounts of phosphorus. The obvious answer is that biological systems in subtropical and tropical ecosystems compete effectively for available phosphorus (and thus limit occlusion of phosphorus) and/or that occluded phosphorus is not necessarily unavailable on the time scale of ecosystem development. In order to model the time scales of ecosystem development with the CENTURY model, we had to modify the representation of phosphorus occlusion so that there is a reverse flow of occluded phospho-... 

Kelly, R.H., Parton, W.J., Crocker, G.J., Grace, P.R., Klir, J., Korschens, M., Poulton, P.R. and Richter, D.D. (1997) Simulating trends in soil organic carbon in long-term experiments using the Century model. Geoderma 81, 75-90. 

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