Project : USDA ARS

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Research Project: Increasing the Utility of Turf in Urban Environments of the Southwest U.S.

Location: Water Management and Conservation Research

2024 Annual Report

Objectives
Objective 1. Develop drought and heat tolerant turf varieties for use in the U.S. Southwest. Objective 2. Expand opportunities for the sustainable utilization of turf in the urban Southwest by reducing input requirements and maximizing related ecological services. Objective 3. Identify and test innovative management practices to increase water use efficiency and improving irrigation water scheduling technologies for turf.

Approach
1. Develop and evaluate drought and heat tolerant turf cultivars for use in the U.S. Southwest. Small plot research will be conducted at the Maricopa Agricultural Center (MAC) in Maricopa, AZ. Focus will be on warm season grasses such as bermudagrass [Cyanodon spp.], but will include other warm- and cool-season turf species suitable to the Southwest U.S. When available, irrigation will be with wastewater from the local water utility. Two levels of irrigation (80 and 50 % of estimated evapotranspiration (ET) replacement) will be examined. Soil water content will be measured weekly using time domain reflectometry in the upper turf root zone (0-0.6 m). Weather data and grass reference evapotranspiration (ETo) is available at the MAC. Plant temperature and turf color and quality will be assessed via weekly remote sensing systems mounted on unmanned aerial vehicles (UAV). Genomic analyses will focus on understanding and characterizing genetic mechanisms association with abiotic stress tolerance. Genomic analysis methods include association studies, high-throughput genotyping, RNAseq and gene expression analyses, genome sequencing and identification, and other forward genetic approaches. 2. Expand opportunities for the sustainable utilization of turf in the urban Southwest by reducing input requirements and maximizing related ecological services. Ecosystem services including carbon sequestration, effects on microclimate and urban habitat will be evaluated at MAC and cooperator sites located in urban Phoenix. Long-term plots irrigated with wastewater will be established at MAC where soil carbon accumulation will be monitored. Soil samples will be collected annually to 2 m and analyzed for carbon, nitrate, and salts. Possible salt buildup and leaching of nitrate to groundwater will be monitored. Effects of turf on the urban microclimate will be evaluated in the urban environment using models, remote sensing and weather station data collected from parks, golf courses and green spaces. Comparisons will be made using matched areas with and without turf. 3. Identify and test innovative management practices to increase water use efficiency and improving irrigation water scheduling technologies for turf. These studies will be conducted in conjunction with those outlined in Objective 1 at MAC. Weekly turf ET will be calculated as the residual of the root zone (0-0.50 m) soil water balance based on changes in measured soil water, measured irrigation and precipitation amounts. Crop coefficients will be determined as the ratio of the soil water balance ET and the ETo from weather data. Water productivity functions will be calculated for biomass yields and quality measures, e.g. color vs. irrigation input and ET. Soil salinity and soil profile nitrate will be monitored with annual soil sampling to 2 m.

Progress Report
This is the final report for the project number 2020-13210-001-000D, titled, "Increasing the Utility of Turf in Urban Environments of the Southwest U.S.", which has been replaced by new project number 2020-21500-001-000D, titled, "Developing Sustainable Turfgrass Systems in the U.S. Southwest". For additional information on future-related research, please see the new project annual report. Substantial progress was made over the last two years of the project, which includes large numbers of germplasm for bermudagrass, zoysiagrass, and native grasses being assembled. Variation for spectral reflectance of bermudagrass was assessed under controlled conditions with significant differences observed among genotypes for reflectance indices related to photosynthetic area and chlorophyll content. Replicated field experiments were established and evaluated under deficit irrigation treatments. Visual and spectral data were collected from the field for two years. Spring green up, turfgrass quality, color, and density data were collected for two years and analyzed. Significant differences were observed among bermudagrass genotypes and performance under deficit irrigation. Data analysis for zoysiagrass, alkali muhly, and alkali sacaton field experiments are in progress. The effects of management practices such as mowing height and water chemistry on turfgrass were studied under a controlled environment. Important results in evapotranspiration, turfgrass growth, and turfgrass quality under deficit irrigation in the arid environment were obtained. The results suggest that specific turfgrass management practices need to be integrated with recycled water irrigation for better turf quality. Progress was made on two of the three objectives and sub-objectives, which fall under NP 215, Component II, Improve the physiology and genetics of plant materials to enhance health, vitality, and utility of pasture, biomass for feed and fuel, rangeland, and turf systems. Progress on this project focuses on Problem 2A, Plant resilience and resistance to stressors; and 2D, Aesthetics and utility of turf. In regard to Objective 1, visual assessment was conducted on the rate of turfgrass establishment, spring green up, turf density, turf color, and quality for two seasons on bermudagrass, zoysiagrass, and native grasses field experiments established under 40, 60, and 80% evapotranspiration replacement (crop coefficient factored) deficit irrigation treatments. The irrigation treatments run from May 1 through October 31. The visual turf assessment data analysis reveals statistically significant differences among bermudagrass hybrids, irrigation treatments, and the genotype-by-irrigation interaction effect. Some drought stress tolerant bermudagrass hybrids were identified. Two years of data collection on alkali muhly and alkali sacaton is in progress. Zoysigrass field experiment, comprising four species, each with a different number of genotypes, was transplanted on May 4, 2022, and deficit irrigation treatment was started on May 1, 2023. First year data has been collected, with year two data collection in progress. Analysis of active reflectance and RGB-image data collected on all the field experiments is ongoing. In support of Sub-objective 2A, turfgrass field plots were established for which four bermudagrass varieties were planted across three reps in two separate treatments including a high management zone and low management zone. These plots will be the basis in which relevant ecosystem services will be recorded and analyzed to represent the capacity for ecosystem services of turfgrass in hot and arid regions. In support of Sub-objective 2B, two studies were conducted to evaluate the impact of water chemistry on hybrid bermudagrass varieties (TifTuf, Tifway, and Midiron) evapotranspiration, growth, and quality. Three water sources (RO, local well, and recycled) each supplied at full irrigation levels (1.0 × ETa) over two, eight-week study periods. It was found that irrigation water quality influences critical factors for hybrid bermudagrass growth and variability exists among three commercially available varieties for ET rates, quality, and shoot growth. Some activities planned under this project will be continued in the newly established project plan.

Accomplishments
1. Genetic diversity of bermudagrass hybrids based on active spectral reflectance characteristics. In the southwestern United States, turfgrass is constrained by drought and heat stresses; concurrently, the availability of water for turfgrass irrigation is increasingly strained. A diverse gene pool allows for the identification of traits that enhance resilience to environmental stressors. ARS researchers in Maricopa, Arizona, characterized turfgrass genetic diversity based on spectral vegetation indices derived from active spectral reflectance, to identify potential hybrids for enhanced photosynthetic area and chlorophyll content that plays a vital role in the quality of the turfgrass under abiotic stresses. The results revealed a prevalence of genotypic difference among 48 turf bermudagrass hybrids for six different vegetation indices.

2. Effect of directional breeding on genetic diversity in hybrid turf bermudagrass. Increasing genetic diversity of commercial cultivars is vital to stress tolerance. A DNA profiling study was conducted of 21 experimental selections from Oklahoma State University in Stillwater, Oklahoma, for a turfgrass breeding program and 11 cultivars using 51 simple sequence repeat markers across the bermudagrass genome. The marker data analysis revealed that directional breeding and selection for cold hardiness or drought resistance generated distinct genetic diversity in bermudagrass. Increasing genetic diversity of the existing cultivar pool with the release of new selections will strengthen and improve bermudagrass turfgrass systems.

3. Interaction of genotypes and irrigation water source affects turfgrass quality and ecosystem services. ARS researchers in Maricopa, Arizona, studied the turfgrass performance of three hybrid bermudagrass varieties (TifTuf, Tifway, and Midiron) using three irrigation water sources (Reverse osmosis (RO), local well, and recycled) each supplied at full irrigation levels (1.0 × ETa) over two, eight-week study periods. It was found that irrigation water quality influences critical factors for hybrid bermudagrass growth and variability exists among three commercial varieties for ET rates, quality, and shoot growth.

4. Mowing height is important in hybrid turf bermudagrass performance in deficit irrigation. The development of turfgrass management for efficient water use is an important need in the turfgrass industry. As one of the important turfgrass management practices, ARS researchers in Maricopa, Arizona, studied four separate mowing heights (2.5, 5.0, 7.5, and 10.0 cm) at full (1.0 × ETa) and deficit irrigation levels (0.65 and 0.30 × ETa). Actual evapotranspiration (ETa), turfgrass visual quality, clipping production, and root development of ‘TifTuf’ bermudagrass were assessed. An elevated ETa was observed at the 7.5 cm and 10.0 cm in two separate 8-weeks studies. A higher root dry weight at higher mowing heights (7.5 and 10.0 cm), clipping production and visual quality was generally higher at lower mowing heights (2.5 and 5.0 cm) for both full and deficit irrigation levels. These results demonstrate that mowing height can significantly influence bermudagrass water use, as well as responses to deficit irrigation. The results from this study indicate a lower water use and improved response to deficit irrigation above 2.5 cm mowing height.

U.S. DEPARTMENT OF AGRICULTURE

Water Management and Conservation Research: Maricopa, AZ