Border fertigation: field experiments and a simple model

Fertilizers are commonly dissolved in border irrigation water. However, there are no available procedures for the proper design and management of surface fertigation. A series of experiments was conducted to determine the uniformity of fertilizer application under varying inflow discharges and fertilizer application times in blocked-end borders. Results from the fertigation evaluations showed that the fertilizer distribution uniformity of the low half (DULH) ranged from 2.9 to 51.6%, while water DULH ranged from 63.5 to 96.9%. A simplified border fertigation model based on one-dimensional convection was formulated and applied to the simulation of the experiments. The model was able to explain 43.8% of the variability in the fertilizer DULH. Application of the model to selected case studies revealed that short-duration applications, such as those resulting from instantaneous release of fertilizer into the irrigation stream, often produce low uniformities. This is particularly true for early applications in blocked-end borders and for early and late applications in level basins. In both irrigation systems, application of fertilizer at a constant rate during the entire irrigation event is frequently the best solution. In the presence of runoff, the model can be used to find a compromise between fertilizer application uniformity and runoff losses. Finally, if large deep percolation losses are expected, the model can identify uniform fertigation options based on late applications of fertilizer.