Simulation of water applied nitrogen distribution under surge irrigation

Fertigation during surge flow irrigation is a promising means of delaying nitrogen (N) fertilizer application on furrow irrigated corn and thereby reducing the potential for leaching of nitrate-nitrogen into groundwater. A computer model, SIFUM (Surge Irrigation Fertigation Uniformity Model), was developed to simulate the distribution, uniformity, and runoff losses of fertigation-applied N during surge irrigation of furrows. The model, SIFUM, was used to help develop fertigation management strategies for field application that can provide acceptable N distributions across a range of soil conditions and furrow flow rates for surge irrigation with free outflow of runoff with no runoff recovery. Simulation groups included injecting N during (a) all surges, (b) the advance surges only, (c) the post advance surges only, and (d) the middle surges (last of advance plus first of cutback). For each of these groups, fertigation was simulated both for the entire on-time of each surge cycle and for only a portion of the on-time. The application efficiency of the low quarter (AELQ) was used as an index for evaluating the efficiency of fertigation treatments. Simulation results show that to obtain the best N efficiency on high-intake soils, fertigation can occur during any portion or all of the on-time of a surge cycle, but should be applied during all cycles, i.e., for the entire irrigation. For medium and low intake soils, fertigation should be applied during all of the on-time of a surge cycle and may be applied for either all of the irrigation or just the advance surges.