Evaluation of electrical resistivity imaging (ERI) for in situ mapping of drip irrigation and fertigation wetting patterns

Drip fertigation is regarded as a precise and efficient method of supplying water and nutrients to tree crops. Despite its widespread use in a range of agricultural industries, there is limited research into the distribution of water and solutes after fertigation and irrigation events. Here, we compare Electrical Resistivity Imaging (ERI) with dye tracer patterns and soil nitrate distribution in a commercial apple orchard in southern Tasmania. Fertigated calcium nitrate was applied with dye tracer through pressure compensated drippers along the treeline of the orchard row. This was followed by a single irrigation event the next day via in-line drippers, split into high and low treatments over the fertigated area. Two dimensional ERI was conducted over a 16 meter length of crop row, immediately before and at four occasions post fertigation. ERI was shown to be a potentially useful tool for mapping infiltration of irrigation and nitrate, as changes in resistivity appeared to be correlated with infiltration, although the contribution to the change in resistivity from irrigation as opposed to the solute content of the fertigation could not be determined. Dye analysis indicated infiltration of water resulted from preferential flow processes whereas infiltration of the nitrate indicated it was absorbed by organic matter within the A1 horizon.