Hybrid Bermudagrass and Tall Fescue Turfgrass Irrigation in Central California: II. Assessment of NDVI, CWSI, and Canopy Temperature Dynamics

Abstract

As the drought conditions persist in California and water continues to become less available, the development of methods to reduce water inputs is extremely important. Therefore, improving irrigation water use efficiency and developing water conservation strategies is crucial for maintaining urban green infrastructure. This two-year field irrigation project (2018–2019) focused on the application of optical and thermal remote sensing for turfgrass irrigation management in central California. We monitored the response of hybrid bermudagrass and tall fescue to varying irrigation treatments, including irrigation levels (percentages of reference evapotranspiration, ETo) and irrigation frequency. The ground-based remote sensing data included NDVI and canopy temperature, which was subsequently used to calculate the crop water stress index (CWSI). The measurements were done within two hours of solar noon under cloud-free conditions. The NDVI and canopy temperature data were collected 21 times in 2018 and 10 times in 2019. For the tall fescue, a strong relationship was observed between NDVI and visual rating (VR) values in both 2018 (r = 0.92) and 2019 (r = 0.83). For the hybrid bermudagrass, there was no correlation in 2018 and a moderate correlation (r = 0.72) in 2019. There was a moderate correlation of 0.64 and 0.88 in 2018 and 2019 between tall fescue canopy minus air temperature difference (dt) and vapor pressure deficit (VPD) for the lower CWSI baseline. The correlation between hybrid bermudagrass dt and VPD for the lower baseline was 0.69 in 2018 and 0.64 in 2019. Irrigation levels significantly impacted tall fescue canopy temperature but showed no significant effect on hybrid bermudagrass canopy temperature. For the same irrigation levels, increasing irrigation frequency slightly but consistently decreased canopy temperature without compromising the turfgrass quality. The empirical CWSI values violated the minimum expected value (of 0) 38% of the time. Our results suggest NDVI thresholds of 0.6–0.65 for tall fescue and 0.5 for hybrid bermudagrass to maintain acceptable quality in the central California region. Further investigation is needed to verify the thresholds obtained in this study, particularly for hybrid bermudagrass, as the recommendation is only based on 2019 data. No CWSI threshold was determined to maintain turf quality in the acceptable range because of the high variability of CWSI values over time and their low correlation with VR values.

Hybrid Bermudagrass and Tall Fescue Turfgrass Irrigation in Central California: I. Assessment of Visual Quality, Soil Moisture and Performance of an ET-Based Smart Controller

“…This study was carried out to (i) determine the response of hybrid bermudagrass and tall fescue to varying irrigation scenarios (level and frequency) in central California, (ii) evaluate the use of an ET-based smart irrigation controller for autonomous irrigation scheduling, (iii) monitor and assess the dynamics of near-surface soil moisture over time under the imposed irrigation scenarios, and (iv) develop regression-based TWRFs and use them to estimate the response of turfgrass species to irrigation scenarios based on long term mean ET o demand in the study region. Part two of this study focuses on applying ground-based remote sensing for turfgrass irrigation management [15]. term mean ETo demand in the study region.…”

“…term mean ETo demand in the study region. Part two of this study focuses on applying ground-based remote sensing for turfgrass irrigation management [15]. The soil at the research site is classified as Hanford fine sandy loam (websoilsurvey.sc.…”

Response of Landscape Groundcovers to Deficit Irrigation: An Assessment Based on Normalized Difference Vegetation Index and Visual Quality Rating

“…Even a well-trained person may introduce bias because the VR process is subjective and prone to rater's fatigue (Horst et al 1984;Luscier et al 2006;Wang et al 2022). The relationship between VR and the NDVI, widely used indicator of vegetative health (Easterday et al 2019;Haghverdi et al 2021c), has been studied in turfgrass plots (Fitz-Rodr ıguez and Choi 2002;Haghverdi et al 2021bHaghverdi et al , 2021cLeinauer et al 2014). In turfgrass research, some studies suggested the use of NDVI as an alternative to visual rating because it provides consistent and reliable evaluation of turfgrass quality in less time compared with visual quality (Bell et al 2009;Fitz-Rodr ıguez and Choi 2002;Haghverdi et al 2021c).…”

“…Haghverdi et al (2021c) introduced the turfgrass water response function as an empirical regression-based model to estimate the response of turfgrass to extreme drought and limited irrigation scenarios. These models were developed using data from turfgrass fields in southern and central California along with long-term weather data obtained from nearby weather stations (Haghverdi et al 2021b(Haghverdi et al , 2021c. Development of these models can be helpful in irrigation management as they estimate the quality (based on NDVI values) of plants for different rates of irrigation.…”

Effects of Deficit Irrigation on Canopy Temperature Dynamics and Physiology of Landscape Groundcovers

“…This phenomenon is based on two assumptions 1) non-water-stressed plants transpire at their full potential and hence maintain leaf temperature lower than air temperature, and 2) when plants are in waterstressed condition, transpiration process decreases and hence increases leaf temperature relative to the air temperature (Andrews et al 1992;Jackson 1982). Moreover, the impact of limited irrigation on the canopy temperature of groundcovers is not well studied, but it is necessary because it helps to evaluate the trade-offs between water conservation and irrigation-induced cooling in urban areas (Haghverdi et al 2021a).…”