Saturday, 15 July 2006

Modelling of Caesium-137 Behavior in a Soil-Plant System.

Onggarbek Alipbeki, Kazakh National Agricultural Univ, Abay, 8, Almaty, Kazakhstan

For studying of transformation caesium-137 regularities in soil and its translocation into the plants, 18 types and subtypes of soils have been taken: soddy-podzolic, gray-brown soils, ordinary sierozems, chestnuts, mountain chestnuts, mountain chernozem, southern chernozem, leaching chernozem and ordinary chernozems. The carried out researches have allowed to make up four types of the models, describing the regularities of caesium-137 migration in soil-plant system: conceptual, statistical, dynamic and integrated cybernetic. In the conceptual (logic) model the conditions and processes determining the mobility of radionuclid in the main depositing subsystem "soil" are submitted in more detail. As the important components of this block are considered: three forms of fallouts (soluble, exchange, fuel particles), three processes (sorbtion, desorbtion and fixing), three forms of connections (immobile, ionexchange and mobile) and three external regulating factors (fertilizers, meliorates and properties of soils). Plants are examined as an object of influence from the soil's part. As the important independent factors of a plant block their biological features, distribution of radionuclids in organs and element-chemical structure are allocated. The developed statistical models as simple monomial equations are parametrizated through calculations of full, partial and plural factors of caesium-137 correlations with physical and chemical properties of soils. They gave the satisfactory results at their comparison with the experimental data through calculations of relative deviations and factors of prediction. The most essential variables of soils, responsible for mobility of radiocaesium in the soil-plant system it is necessary to consider the size of absorption capacity and the contents of exchange potassium and calcium in soil. The dynamic models for which basis of calculation the factors of radionuclid diffusion in soil have been taken, and also caesium-137 imitating migrations on their accuracy did not exceed the reliability, which were received with the help of the statistical models. Therefore the dynamic models must be considered as research for which the further completion of separate parts of the mathematical device is required. The cybernetic (logic) model of management by intensity of caesium-137 migration in a soil-plant system, which is integrated in agrobiocenosis, is developed. It is consisted of four independent, interconnected blocks with the feedback and external output. The integrated cybernetic model provides a complex estimation of the chosen administrative decision, which should provide with the requirements of ecological restrictions. The offered model takes into account the complexity and nonstationary of agrosphere as an object of management and stochasticity of decision-making processes.

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