Assessing suitability of modified center pivot irrigation systems in corn production using low altitude aerial imaging techniques

This study evaluated corn (Zea mays var. indentata) canopy vigor and temperature variations using small unmanned aerial system (UAS) based spatiotemporal imagery data. The key objective was to develop understanding on site-specific suitability of the Mid Elevation Spray Application (MESA) and Low Elevation Spray Application (LESA) sprinkler systems in irrigating corn crop and potential water as well as energy savings. Aerial data was collected through small UAS flights at 100 m height above ground level and on 49, 59, 65, 77, 105, 114, 134 days after planting (DAP). Small UAS had 5-band multispectral and radiometric thermal imager on-board the platform. Custom image processing algorithms were developed to extract various vegetation indices (Normalized difference vegetation index [NDVI], Green NDVI [GNDVI] and Normalized difference red edge [NDRE]) and canopy temperature maps from the imagery data. Two sample T-test was performed on extracted data to understand significant difference, at 5% level, within the LESA and MESA treatments. For both the irrigation techniques, the crop vigor increased in the early growth stage (49, 65 DAP), peaked in the mid growth stage (77, 105, 114 DAP) and then decreased in the late growth stage (134 DAP). The MESA irrigated sections had higher vigor (NDVI, GNDVI, NDRE), but not significant, compared to LESA throughout the season. Similarly, the MESA irrigated areas had significantly (0.61–2.07 °C) cooler canopies than LESA. Such results were anticipated, in part due to the issues with the sprinkler heads used in LESA. The heads were being pulled off in the corn field, causing the weighted hose to damage the crop. A different kind of sprinkler head was used after this incident. However, some strips of corn had already been damaged. Overall, this study results confirm suitability of aerial imagery data in evaluating pertinent irrigation treatments. Additional season’s data would be needed to clearly understand which technique (LESA or MESA) is more suitable for irrigating corn crop in the central part of state of Washington. Keywords: Mid Elevation Spray Application, Low Elevation Spray Application, Crop vigor, Crop water stress, Multispectral imaging, Thermal imaging