Development of some Models for Assessment the Dynamic Migration Processes of Phosphates in Soil Columns

Due to complexity of phosphate (P) migration in soil columns, the problem of theoretical approach of modeling the process is specialy diffi cult. So, numerous semiempirical models based on admission of simplifying assumptions were developed, some of them being apart from the real phenomenon. In this paper are presented the breakthrough curves, the phosphate (P) usage degree in soil, based on a dynamic study, realised in order to determine phosphate sorption rate on the granules of two soil types (cambic chernozem and psamosoil) from Romania. Due to random character of the process, which is influenced by many naturally variable factors, this can be addressed from stochastic point of view. Experimental data regarding phosphate migration in soil column evolution process are represented like curves with sigmoid profi le. Based on this observation, Rosin- Rammler and Schuhman sigmoid profi le curves, known models and logistic type equations were used as simulation models representing phosphate transport and sorption kinetics for laboratory experiments in columns. Testing the models with the experimental data resulted with the conclusion that the most appropriate models describing the process of phosphate migration in soil columns are Rosin-Rammler and logistic type equation, C = 1-exp(-btn) and C = [1+exp(?+?t)]-1, (C – relative concentration; t – time; b, n, ?, ? - constant coeffi cients determined from experimental data by non-linear regression) for which the correlation coeffi cient is R2 ? 0.983 for both types of soil.