Abstract:
This study “Modeling Nitrate Transport with Dispersion in Soil”. presented finite element and empirical models to predict transport of nitrates in a soil. Three different soil samples were selected which includes sand, clay and silty soil. Each sample was gradually introduced into a fabricated iron column, having a length of horizontal column 30cm and vertical part 60.96cm. A solution of silver nitrate was allowed to pass through the vertical column down to the horizontal part. Samples of soil were collected at a constant distance of 10cm and time interval of 5mins for 60mins .The concentration of nitrate was taken at a constant distance of 10cm .This was done three times for each of the soil sample. Thereafter, the dispersion coefficient was calculated, and a regression dispersion model developed as a function of permeability, average diameter of sieve, velocity of flow and time taken to flow. The model was verified with experimental results and found to have a high correlation of 0.958. The prediction of the derived model were compared with those in literature. Data obtained from the experiments were fitted into the two existing models (Shao, 2017; and De Smeldt and Wierenger 1978) and poor correlation coefficients of -0.529 and -0.524 were obtained, respectively. The regression dispersion model developed was incorporated into Notodarmojo model. Both the Notodarmojo and the modified models were solved using finite element methods. Then, the two equations were used to predict the variation concentration of nitrate with distance. The results showed that the concentration of nitrate decreases as the distance increases. In addition the modified transport equation gave a better prediction of the variation of nitrate concentration with distance than the Notodarmojo’s equation. The r values for the two ranged from 0.741 to 0.896 and 0.484 to 0.769 for the modified model and Notodarmojo model, respectively. Using the Student t- test, the predicted values were significant to each other ranging from 0.0074 to 0.331.The research has established that the modified model which accounted for variability in dispersion coefficient offered a better approach than the conventional one.
