The application uniformity of sprinkler irrigation systems affects both crop growth and profitability. However, traditional catch can measurements of irrigation uniformity are labour intensive and are normally only conducted in a small area of the field. A trial was established in a lettuce crop irrigated with a solid set sprinkler system to evaluate the potential to use electromagnetic sensing for irrigation performance assessment. After crop establishment, the uniformity of the irrigation applications was deliberately modified within two sprinkler plots (9 m x 11 m) by reducing the sprinkler operating pressures. The uniformity of the water applied during each irrigation was measured using a grid of catch cans. The apparent soil electrical conductivity (ECa) was measured within the plots for each irrigation during the cropping season using an EM38. Electromagnetic (EM) measurements were taken with the EM38 either on the ground or 35 cm
above the ground surface. Elevating the EM sensor above the ground level did not improve the correlation between the point measured catch can volume of water applied and the difference in ECa measured before and after irrigation (ECa). However, the coefficient of uniformity calculated using the ECa data was correlated to the coefficient of uniformity calculated from the catch can data. The correlation was improved where the EM sensor was elevated above the soil surface so that only the root zone was sensed. This suggests that measurements of ECa can be used to estimate the irrigation uniformity for shallow rooted crops, particularly when the uniformity is low (CU < 70%) and the irrigation application pattern is consistent throughout the season. ECa measurements also identified the location of irrigation system leakages within the field
