Indirect Measurement Of Creeping Bentgrass N, Chlorophyll, And Color For Precision Golf Green Management
Indirect measurement of turfgrass tissue through optical sensing may provide golf course managers with non-destructive and relatively simple real-time measurements of golf green N requirements. The objective of this study was to determine the effect of N rate on ‘Crenshaw’ creeping bentgrass (Agrostis stolonifera L.) tissue N, chlorophyll concentration, and color using the GreenSeeker (NTech Industries, Ukiah, CA) handheld sensor. Plots (0.9 X 1.5 m) were established at the Oklahoma State University Turfgrass Research Center in Stillwater, OK in a randomized complete block design with 4 replications and plots were evaluated over two growing seasons. Treatments consisted of plots fertilized with 0, 6.1, 12.2, 24.4, 36.6, and 48.8 kg N ha-1 yr-1. Normalized difference vegetative index (NDVI) and green normalized difference vegetative index (GNDVI), tissue collection (N and chlorophyll), and color ratings (1-9 scale) were recorded every 15 d. Normalized difference vegetative index, GNDVI, tissue N, chlorophyll content, and visual color ratings significantly increased with increasing N application rates. Linear regression of N rate with tissue N (n = 576) and chlorophyll content (n = 264) from all data combined were significant (P < 0.01), positive relationships. The strength of these relationships were r2 = 0.07 for tissue N and r2 = 0.03 for chlorophyll content. Linear regression of NDVI and GNDVI with tissue N from all data combined were highly significant (P < 0.0001), positive relationships. The strength of these relationships were r2 = 0.46 for NDVI (n = 576) and r2 = 0.26 for GNDVI (n = 288). NDVI was a better indicator of creeping bentgrass tissue N and visual color than GNDVI. NDVI may prove to be a useful tool for the potential of creating a variable rate N fertilizer applicator for precision N management on golf greens.