Relationships between Normalized Difference Vegetation Index and Visual Quality in Turfgrasses: Effects of Mowing Height

Abstract

Canopy spectral reflectance may provide an objective means to evaluate visual quality of turfgrass, but evaluations of quality may be confounded by cultural practices that affect reflectance, such as mowing height. In this 2‐yr study near Manhattan, KS, we examined effects of mowing height on relationships between normalized difference vegetation index (NDVI) and visual quality ratings in Kentucky bluegrass (KBG; Poa pratensis L., ‘Apollo’) and in a KBG × Texas bluegrass (Poa arachnifera Torr.) hybrid (HBG; ‘Thermal Blue’). Mowing heights were 7.62 cm (high) and 3.81 cm (low). The NDVI averaged 4.5 to 7% greater in high‐ than in low‐mown plots. Distinct regression models of visual quality were found at each mowing height and in each species (r2 from 0.40 to 0.81); separate relationships between NDVI and visual quality were also found between years in the same plots. Correlations between NDVI and visual quality were stronger at high than at low mowing heights, possibly because of greater green biomass at high mowing heights. The 95% confidence intervals surrounding predictions of visual quality from NDVI ranged from ±1.34 to 2.75 (on a 1‐to‐9 scale). Thus, lack of precision is a concern when using these models for detection of differences between treatments. Results indicate that when using NDVI to evaluate turfgrass quality, evaluations should be limited to plots maintained at the same mowing height and with the same species to reduce variability in NDVI.

Relationships between Normalized Difference Vegetation Index and Visual Quality in Cool‐Season Turfgrass: I. Variation among Species and Cultivars

“…X C. transvaalensis Burtt Davy, 'Midiron']. In other studies, vegetation indices calculated from reflectance data were also strongly correlated with visual quality in a number of turfgrass species and under different cultural practices (Bell et al, 2002;Fitz-Rodriguez and Choi, 2002;Keskin et al, 2008;Lee et al, 2011).…”

“…In fact. Lee et al (2011) compared models between two turfgrass species over 2 yr and reported that the models were different between species and between years within each species.…”

“…Therefore, in this 3-yr study our objectives were to statistically compare models of relationships between normalized difference vegetation index (NDVI) and visual quality ratings among four turfgrasses using the same method as Lee et al (2011), who, in research investigating the effects of mowing height on NDVI, only evaluated two grasses over 2 yr. We evaluated relationships between NDVI and visual quality in Kentucky bluegrass, two hybrid bluegrasses, and tall fescue, which are all cool-season turfgrasses.…”

Using hyperspectral radiometry to predict the green leaf area index of turfgrass

“…30-0.40. ) Most vegetation indices in turfgrasses have been developed using multispectral, or broadband, radiometry (Trenholm, Carrow, and Duncan 1999;Jiang and Carrow 2007;Bremer et al 2011aBremer et al , 2011bLee et al 2011), including in the study described above by Lee (2008). Multispectral radiometry measures the spectral reflectance of plant canopies in a few bands (e.g.…”

“…The variations in model strength and viability may be related to changes in the density of Kentucky bluegrass during the growing season. For example, in the study area the green biomass of Kentucky bluegrass typically increases during early spring but may decrease during middle to late summer when it is under heat stress (Bremer et al 2006;Lee et al 2011). There may be additional, poorly understood factors of the turfgrass canopy that change over the course of the growing season (e.g.…”