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Uniform rate irrigation on variable soil landscapes can cause spatial differences in plant available water, which leads to inconsistent crop yields as well as the inefficient use of water resources and irrigation infrastructure. Variable rate irrigation has the potential to increase water use efficiency and reduce spatial variability in plant available water by customizing irrigation applications across variable soil landscapes. Variable rate irrigation is implemented by delineating a field into management zones with relatively homogeneous available water holding capacity. These have traditionally been delineated using soil apparent electrical conductivity (ECa) mapping; however, concerns with interference from soil salinity and laborious data acquisition has created a demand for new ways of identifying spatial variability in available water-holding capacity (AWC). One emerging approach for this is based on interactions of plant stress response to soil moisture conditions inferred using remote sensing techniques. This thesis introduced and field-tested two methods of delineating irrigation management zones that utilize remote sensing indices to measure plant response during a drydown scenario. The indices examined were apparent canopy temperature and normalized difference vegetation index (NDVI). The traditional (ECa) and emerging (apparent canopy temperature and NDVI) zone delineation methods were compared by testing the ability of these methods to identify spatial variability in AWC between 48 sample locations in a 16-ha irrigated field in Outlook, Saskatchewan. Available water holding capacity was quantified at the 48-sampling locations by determining the water retention characteristic of soil horizons that differ in texture using the pressure plate method. Soil apparent electrical conductivity (ECa) was acquired via EM38-Mk2 survey on bare soil. Apparent canopy temperature and NDVI remote sensing data were acquired via unmanned aerial vehicle (UAV) during early and late stages of a drydown scenario on an established wheat crop. As the field dried, spatial variability in plant available water became apparent between areas in the field with low and high AWC, which helped to develop a relationship between the plant response methods and AWC. The apparent canopy temperature method was found to outperform the traditional zone delineation methods under both early and late drydown conditions, whereas the NDVI method was only able to outperform ECa under late drydown conditions. This is a substantial limitation for NDVI because the late drydown conditions caused crop damage in areas of the field with low AWC. The ECa method was found to accurately identify spatial variability in AWC at the field site; however, this method performed poorly in salinity affected soils. Apparent canopy temperature has the potential to be a suitable replacement for traditional zone delineation methods, as this method was able to delineate accurate management zones under minor drydown conditions, which did not cause apparent crop damage in wheat. However, the utility of this method can be diminished by crop damage and error caused by variable cloud cover during data acquisition. The practical considerations and abilities of each method to identify spatial variability in AWC are key factors for determining the most practical method or combination of methods to utilize for delineating management zones for variable rate irrigation.



Variable Rate Irrigation, Management Zone Delineation, NDVI, Thermal Sensing



Master of Science (M.Sc.)


Soil Science


Soil Science


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