Modelling of energy flows and conversion efficiencies in a grassland ecosystem
1986
Shiyomi, M. | Akiyama, T. | Takahashi, S.
A grassland ecosystem is usually made up of many environmental and biological factors which consitute the production factors in the ecosystem, and the interactions between them are intricately entangled with each other. In this study, a system model of energy flows in arable lowland grassland in central Japan is considered. The model is composed of the following seven compartments: above-ground plant biomass, below-ground live biomass, standing dead material, surface litter, herbage ingested by grazing cattle, cattle biomass and feces; and the following two energy flows are dealt with: (1) sun → plants → standing dead material → litter → soil organic matter; and (2) plants → cattle. Energy flows between the seven compartments are described by eight simultaneous differential equations, and parameters in the model were determined from field experiments. The results are as follows: an optimal stocking rate with increases in total cattle body weight obtained during the year can attain a maximum when cattle with a total body weight of 1625 kg/ha, at the beginning of the grazing season, were grazed. Energy flows under such conditions are as follows, in kJ m−2 year−1: global solar radiation (ca. 473 × 104) → photosynthetically active radiation (ca. 191 × 104) → energy fixed in above-ground plant portion (17 460) → energy grazed by cattle (17 468) → net seconndary production (761).
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