Phosphorus in the soil-plant-animal ecosystem : An introduction to a model

A compartmental model of phosphorus in soil-plant-animal ecosystem is described. It consists of 17 compartments, five in soil, six in plant, three in above ground fauna and three in soil organisms and microorganisms. Common amounts and rates of turnover in each of these compartments is presented. Though the total amount of P in the ecosystem is large, only a very small part of it is being cycled, and presented data show that removal of P from an agricultural pastoral ecosystem is very slight. Most of the available phosphorus which is absorbed by plant roots is gradually fixed in forms of long-range unavailability, both by plants and by animals. This process of biological fixation is counterbalanced mainly by the activity of soil microorganisms. Quantities of input-output of P in intensive pastoral ecosystems are also presented, and some agronomical and ecological implications are considered. The manipulation of soil microorganisms and change towards more desirable P releasing strains or species may decrease need of fertilization, lower the risk of eutrophication and enhance productivity of such ecosystems. Such manipulations, however, can be achieved only after appropriate research.