Sampling patterns may influence the evaluation of irrigation uniformity of Center Pivot systems

The evaluation of irrigation uniformity can be affected by the sampling pattern in the field. Thus, this work aimed to compare the water application uniformities of a Center Pivot using three sampling patterns: along the equipment radius (radial), in the direction of movement of the pivot (circular) and in a two-dimensional way (meshed). For this, samplers were positioned under the spans of a Center Pivot system, being evaluated the effects of the sampling pattern and of the span, in a 3x3 statistical factorial design, with three replications. The results showed that circular and meshed arrangements were statistically equal and had higher values of Christiansen's and Distribution Uniformity Coefficients. The mesh type arrangement represented a more uniform distribution profile of irrigation depths on the surface. For areas of flat or slightly undulating topography and when using pressure regulating valves for the emitters, sampling in a radial pattern is sufficient, but for terrains with irregular topography or when pressure head variations along the lateral line are important for the operation of the emitters, the combination of the radial and circular pattern is interesting. The meshed sampling detects the stoppage effect of the towers and drift, however, in a reduced area.