NITRINET: A predictive model for nitrification in reclaimed water distribution in pressurised irrigation networks

In this work, a new model (NITRINET) to simulate nitrification processes in pressurised irrigation distribution networks fed with reclaimed water is developed and applied to the Tintín Irrigation District distribution network as case study (Montilla, southern Spain). The importance of this model relies on the fact that the nutrient chemical composition of reclaimed water varies spatially along the network. The water quality analyses carried out in the Irrigation District have shown that nitrate concentrations increase along the distribution network in contrast to the reduction observed in the ammoniacal forms. This confirms that nitrification processes occur inside the pipes. Thus, the model combines the hydraulic simulation of the distribution network and the modelling of nitrification processes to predict the concentration of ammoniacal nitrogen (NH4+-N) and nitric nitrogen (NO3--N) in water arriving at farms. This model is of great applicability to the irrigation sector, given that to carry out precision fertigation strategies and optimise the amount of fertiliser applied, it is necessary to determine the concentration of nutrients present in water arriving at farms. The nutrients that reclaimed water already carries must be considered when planning fertilisation. This allows for a reduction in the amount of fertiliser applied to the soil, which has a positive impact both on the environment and on farmers’ incomes. Simulations performed with NITRINET have shown promising results, predicting the concentration of NH4+-N and NO3--N in irrigation water with mean absolute errors of 1.49 mg·L−1 and 1.25 mg·L−1, respectively.