Developing Equations to estimate Nitrate Distribution Pattern in Subsurface Drip Irrigation Systems

Background and objective: Drip irrigation with fertigation provides an effective and economical way to supply water and nutrients to crops. However, less-than-optimum management of micro irrigation systems may cause inefficient water and nutrient use, thereby diminishing expected yield benefits and contributing to ground water pollution if water and nitrogen applications are excessive. The quality of ground, and surface waters is specifically vulnerable in dry regions where agricultural production occurs mostly by irrigation. Robust guidelines for managing micro irrigation systems are needed so that the principles of sustainable agriculture are satisfied.
Materials and methods: Simulation of nitrate distribution in soil by means of found early parameters can effectively help to design the subsurface drip irrigation system. In this study, in order to develope equations to estimate the nitrate distribution, the experiments was carried out on three different soil textures and in different directions. In this study, experiments were carried out in a transparent plexy-glass tank (0.5m.1.22m.3m) using three different soil textures (fine, heavy and medium). The drippers were installed at 3 different soil depths (15cm, 30ch and 45cm). The emitter outflows were considered 2.4 , 4 and 6 lit/hr with irrigation duration of 6hr. The fertigation treatments include treatments with nitrate concentrations of 125, 250 and 375 mg per liter. The fertigation treatments include treatments with nitrate concentrations of 125, 250 and 375 mg per liter. In order to fulfil the fertigation treatments was used urea (CH4N2O) (46% nitrogen).
Results: Then, using the- theorem of Buckingham and Dimension Analysis (DA), equations were developed to estimate the pattern of nitrate distribution pattern (horizontal and vertical) in three soil textures. These equations are as function of initial nitrate, nitrate concentrations in fertigation, initial moisture, radial distance of points, applied water volume, hydraulic conductivity and emitter outflows. The results of the measured and simulated values for suggested models of nitrate distribution showed that despite the complexity of this ion, specifically the nitrate distribution in different conidtions (due to the interactions and reactions of nitrates in the soil due to the phenomenon of the nitrification and denitrification), have a good performance. Result showed that error statistical parameters related to comparisons between simulated and observed values are in an acceptable range.
Conclusion: The results of the comparisons between simulated and observed values showed that these equations are very capable in predicting the pattern of nitrate distribution in different directions. Considering these equations in designing surface drip irrigation systems could improve system performance.