Optimum Design of Alternate and Conventional Furrow Fertigation to Minimize Nitrate Loss

Alternate-furrow fertigation has shown potential to improve water and fertilizer application efficiency in irrigated areas. A combination of simulation and optimization approaches permits researchers to identify optimum design and management practices in furrow fertigation, resulting in optimum cost, irrigation performance, or environmental impact. The objective of this paper is to apply one-dimensional (1D) surface and two-dimensional (2D) subsurface simulation-optimization models to the minimization of nitrate losses in two types of alternate-furrow fertigation, as follows: (1) variable alternate-furrow irrigation, and (2) fixed alternate-furrow irrigation. For comparison purposes, optimizations are also reported for conventional furrow irrigation. The model uses numerical surface fertigation and soil-water models to simulate water flow and nitrate transport in the soil surface and subsurface, respectively. A genetic algorithm is used to solve the optimization problem. Four decision variables (inflow discharge, cutoff time, start time, and duration of fertilizer solution injection) were optimized to minimize the selected objective function (nitrate loss) for two fertigation events performed during a maize-growing season. The simulation-optimization model succeeded in substantially reducing the value of the objective function as compared with the field conditions for all irrigation treatments. In the experimental conditions, optimization led to decreased inflow discharge and fertilizer injection during the first half of the irrigation event. This was because of the high potential of the field experiment to lose water and nitrate through runoff. In the optimum conditions, alternate-furrow fertigation strongly reduced water and nitrate losses compared with conventional furrow irrigation. The simulation-optimization model is a valuable tool for alleviation of the environmental impact of furrow irrigation.