Simulation of Nitrate Distribution Pattern in Surface Drip Irrigation Systems Using Dimensional Analysis

Drip irrigation has a priority in selecting an appropriate irrigation method in arid and semi-arid regions because of its potential of precisely applying water and chemicals both in quantity and position. Proper design and management of a drip fertigation system is, to some extent, dependent upon a better understanding of wetting patterns and water and solute distributions in soil under different combinations of soil type and layering, emitter application rate, volume applied and fertigation concentration. In this study, experiments were carried out in a transparent plexiglass tank (0.5 x1.22 x 3 m) using three different soil textures (light, heavy, and medium). The emitter outflows were considered 2.4, 4, and 6 lit/hr with irrigation duration of 6 hr. The fertigation treatments included treatments with nitrate concentrations of 125, 250, and 375 mg/L. Urea fertilizer (CH4N2O) (46% nitrogen) was used in the fertigation treatments. Then, using the p theorem of Buckingham and Dimension Analysis (DA), equations were developed to estimate the pattern of nitrate distribution pattern (horizontal and vertical) in the three soil textures. The equations developed were functions of initial soil nitrate content, nitrate concentrations in fertigation, initial moisture, radial distance of points, applied water volume, hydraulic conductivity, and emitter outflows. The results of the comparisons between simulated and observed values showed that the equations were capable of predicting the pattern of moisture distribution in different directions. The averages of Root Mean Square Error (RMSE) values in clay soil and for emitter outflows 2.4, 4, and 6 lit/hr were 0.025, 0.105 and 0.093, respectively. These values for loamy soil were 0.032, 0.052, and 0.05, respectively, and for sandy soil were 0.023, 0.038, and 0.035, respectively. Considering these equations in designing surface drip irrigation systems could improve system performance.