Evaluation of several sampling procedures for spatial analysis of natural turfgrass sports field properties

Spatial analysis of sports field properties are valuable for the development of a site-specific management program. Our objective was to evaluate six sampling grid sizes (2.4 m × 4.8 m, 4.8 m × 4.8 m, 4.8 m × 9.6 m, 9.6 m × 9.6 m, 9.6 m × 19.2 m, and 19.2 m × 19.2 m) for the spatial analysis of volumetric water content (VWC), penetration resistance, and normalized difference vegetative index (NDVI) on two football fields (sandy loam and sand capped soils) near field capacity and under drier soil conditions. Descriptive statistics and geostatistical methods (spatial maps and kriging variances) were employed to compare results of the sampling grid sizes. Spatial variations of measured properties between soil moisture conditions were minimal for each sampling grid size; however, the magnitude of VWC and penetration resistance was strongly influenced. Small-scale variability of VWC decreased on maps created from the 9.6 m × 9.6 m sampling grid and greater, but large scale variability was evident with most sampling grids. Small-scale variability of penetration resistance was more noticeable on the native soil field, while comparable maps were observed for all sampling grids between 2.4 m × 4.8 m and 9.6 m × 9.6 m when the field was near field capacity. On the sand capped field, the 19.2 m × 19.2 m sampling grid produced the only incomparable map of penetration resistance, regardless of soil moisture condition. NDVI results were influenced by paint present on each field. It is recommended that sports field managers begin with a 4.8 m × 9.6 m sampling grid to conduct a baseline standard of field properties when soil is near field capacity. Subsequent sampling should be conducted under similar soil moisture conditions with the baseline used for comparison over time. The sampling grid can be adjusted depending on the variability of the field property and desired accuracy.