Models Organism and Process Oriented

A recurrent theme that resonates throughout the field of soil ecology is the focus on organisms and population dynamics models used by community ecologists, and the use of process models at the ecosystem scale (Moore et al., 1996; Smith et al., 1998). Many ecosystem level models have included dynamics of the soil biota only implicitly, yet the intrasea-son dynamics of microbes and fauna, as is demonstrated in Chapters 4 and 5, often have a significant effect on nutrient availability and turnover. One of the more successful combinations of the organismal and process modeling approaches was by Paustian et al. (1990), who used four cropping systems (both annual and perennial crops) that varied in inorganic inputs and organic production in the growing season: (1) barley without fertilizer, (2) barley fertilized with 120kgNha-1yr-1, (3) a meadow fescue field with 200kgNha-1yr-1, and (4) a lucerne field with indigenous nitrogen fixation. The conceptual models of carbon and nitrogen flows in the four fields are presented in Figures 3.14 and 3.15 (Paustian et al., 1990). Although there were no large differences in microbial biomass between treatments, the estimated microbial

Barley 0

Barley 120

Grass ley

Lucerne ley

FIGURE 3.14. Budgets of annual carbon flows (gCm-2yr-1) for barley receiving no nitrogen fertilizer (B0), barley receiving 120kgNha-1 (B120), a grass ley receiving 200kgNha-1 (GL) and a N2-fixing lucerne ley (LL). Budgets are based on data from 1982-1983 for the topsoil (0-27cm). Compartment changes on an annual basis are denoted by delta (A) symbols; for the aboveground plant compartment this includes biomass, standing dead litter, and surface litter. Soil organic matter (SOM), including microbial biomass and soil litter, has been combined into a single compartment. NCCA is net canopy carbon assimilation (from Paustian et al., 1990).

FIGURE 3.14. Budgets of annual carbon flows (gCm-2yr-1) for barley receiving no nitrogen fertilizer (B0), barley receiving 120kgNha-1 (B120), a grass ley receiving 200kgNha-1 (GL) and a N2-fixing lucerne ley (LL). Budgets are based on data from 1982-1983 for the topsoil (0-27cm). Compartment changes on an annual basis are denoted by delta (A) symbols; for the aboveground plant compartment this includes biomass, standing dead litter, and surface litter. Soil organic matter (SOM), including microbial biomass and soil litter, has been combined into a single compartment. NCCA is net canopy carbon assimilation (from Paustian et al., 1990).

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Harvest 3.6

Seed Fertilizer N + deposition

Gaseous losses +

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