Turfgrass quality decreases when grown on fine textured soils that are irrigated with poor quality water. As a result, sand-capping (i.e., a sand layer above existing native soil) is now considered during golf course fairway renovation and construction. Mapping spatial variability of soil apparent electrical conductivity (ECa) has recently been suggested to have applications for precision turfgrass management (PTM) in native soil fairways, but sand-capped fairways have received less attention. The objective of this study was to use electromagnetic induction (EMI) to investigate the spatial relationship of ECa with turfgrass and soil characteristics in sand-capped fairways from two golf courses in TX. Both courses had a target sand-capping depth of 20.3 cm during fairway construction; however, one was built in 2001 with ‘Tifway 419’ bermudagrass and the other in 2005 with ‘Zeon’ zoysiagrass. Data were collected on two fairways at each course in April 2021. Apparent electrical conductivity (mS/m) was measured at a 0.5-m depth using a tow-behind DUALEM-1S electromagnetic geophysical instrument. Georeferenced soil moisture (% volumetric water content) and penetration resistance (MPa) data were collected at a 10.2-cm depth using a tow-behind Toro Precision Sense 6000 (PS6000). The PS6000 also measured normalized difference vegetation (NDVI) with two GreenSeeker Model 500 active sensors. An 8.5 m2 sampling grid was generated for each fairway in ArcMap and imported into a Trimble Geo 7X that was used to identify locations for measuring soil moisture and ECa at a 12.2-cm depth with a handheld FieldScout TDR 350. Depth of organic layer (mm) was also measured using a soil core with a digital caliper at the same identified locations. Interpolation of turfgrass and soil characteristics was done in ArcMap using ordinary kriging. Values from maps generated using DUALEM-1S and PS6000 data were extracted to the sampling grid locations, and then used in correlation coefficient calculations for assessing the strength and direction of relationships between all measured variables (α=0.05). Correlation coefficients with EMI ECa on all fairways were positive for PS6000 (r=0.13 to 0.63) and handheld (r=0.19 to 0.61) soil moisture, although the relationships were only statistically significant on three and two fairways, respectively. There were also positive relationships between EMI ECa and handheld ECa on all fairways (r=0.25 to 0.56), and these relationships were statistically significant on three fairways. Organic layer depth and penetration resistance correlation coefficients with EMI ECa were all positive (r=0.08 to 0.32) and negative (r=-0.13 to -0.50), respectively, yet the relationships were statistically significant on only one fairway. The NDVI and EMI ECa relationships were positive and significant on zoysiagrass fairways (r=0.34 and 0.45), but not significant and had mixed directional trends on bermudagrass fairways (r=-0.10 and 0.20). Results indicate that mapping ECa using EMI may be used in sand-capped fairways for certain PTM practices; nevertheless, inconsistent strength and direction of relationships in fairways within and between golf courses warrants further research.
