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Abstract

Ten flowering annuals were greenhouse-grown and irrigated with four levels of saline water [electrical conductivities (EC) = 0.8, 1.5, 3.0, 4.5 dS·m⁻¹] to determine their response to increased salinization. Twelve different parameters were monitored at the end of an 8-week period. All 10 species differed in their response to salinization. The relative number of flowers and the relative maximum flower diameter at harvest decreased significantly for six of ten and seven of nine species, respectively, with increased salinity. A salt tolerance scale was devised that best described their response to salinity. The parameters selected were dry weight, plant height, number of flowers, and maximum flower diameter. Cosmos (Cosmos bipinatus Cav. ‘Sunny Gold’) was rated very sensitive for all four parameters. Following Cosmos, the rating changed and so did the sequence, depending on the parameter being considered. Both petunias (Petunia hybrida Linn. ‘White Cascade’ and ‘Challenger White’) and dianthus (Dianthus chinensis Linn. ‘Princess White’) were the only species rated very tolerant for all four parameters.

A 2-year study was conducted to quantify the actual evapotranspiration (ET_a) of three woody ornamental trees placed under three different leaching fractions (LFs). Argentine mesquite (Prosopis alba Grisebach), desert willow [Chilopsis linearis (Cav.) Sweet var. linearis], and southern live oak (Quercus virginiana Mill.) (nursery seedling selection) were planted as 3.8-, 18.9-, or 56.8-liter container nursery stock outdoors in 190-liter plastic lysimeters in which weekly hydrologic balances were maintained. Weekly storage changes were measured with a portable hoist-load cell apparatus. Irrigations were applied to maintain LFs of +0.25, 0.00, or -0.25 (theoretical) based on the equation irrigation (I) = ET_a/(1 - LF). Tree height, trunk diameter, canopy volume, leaf area index, total leaf area (oak only) and dry weight were monitored during the experiment or measured at final harvest. Average yearly ET_a was significantly influenced by planting size (oak and willow, P ≤ 0.001) and leaching fraction imposed (P ≤ 0.001). Multiple regressions accounting for the variability in average yearly ET_a were comprised of different growth and water management variables depending on the species. LF, trunk diameter, and canopy volume accounted for 92% (P ≤ 0.001) of the variability in the average yearly ET_a of oak. Monthly ET_a data were also evaluated, with multiple regressions based on data from nonwater-deficit trees, such that LF could be ignored. In the case of desert willow, monthly potential ET and trunk diameter accounted for 88% (P ≤ 0.001) of the variability in the monthly ET_a. Results suggest that irrigators could apply water to arid urban landscapes more efficiently if irrigations were scheduled based on such information.

Golf course superintendents in the southwestern United States (Tucson, Ariz.; Phoenix, Ariz.; Las Vegas, Nev.; Orange County, Calif.) were surveyed to assess attitudes toward using reuse water for irrigation. Eighty-nine golf course personnel returned the survey, with 28% indicating that they irrigate with municipal water, 36% with well water, and 27% with reuse water. The reason for switching to reuse water varied by state, with 40% of respondents switching in Arizona because of mandates, 47% switching in Nevada because of cost incentives, and 47% switching in California because it was considered a more reliable source of water. Less than 20% of the respondents rated the use of reuse water on golf courses and parks to have a negative impact on cost, the environment and health. However, respondents indicated that using reuse water does have a negative impact on the operations of the golf course, with pond maintenance and irrigation maintenance having the highest negative impact (∼80%). Multiple regression analysis revealed that among those who indicated that using reuse water would have a negative impact on golf course management, a higher percentage were individuals who had a greater number of years of experience irrigating with reuse water (P = 0.01) and individuals who have taken classes on how to use reuse water (P = 0.05). Respondents who currently irrigate with reuse water indicated they had changed a wide range of landscape and turfgrass management practices as a result of using reuse water. Based on the results of this survey, it was concluded that golf course personnel in the southwestern U.S. do not oppose the transition to reuse water for irrigation. However, it was also clear they recognize using such water negatively impacts their golf courses' operations.

When comparing states with population percentages residing in major cities, Nevada is considered the third most urban state in the nation. It also has the distinction of being the driest, with less than 4 inches of precipitation annually in the Las Vegas Valley. Nevada is using 280,000 acre-feet of water from its 300,000 acre-feet allotment from the Colorado River annually. Approximately 60% of this is used for urban landscaping. With average water use at >300 gallons per person per day in the past, Las Vegans have been criticized as “water-wasters.” Rising water prices and an active research and extension education program begun in 1985 and supported by the local water utility has helped to contribute to changing water use patterns and a reduction in water use. Research, educational programs for commercial landscapers, and home horticulture programs conducted through Master Gardeners have helped to reduce water use in the Las Vegas Valley while providing information on sound horticultural practices.

Research was conducted to assess the response of tall fescue (Festuca arundinacea Schreb.) to water deficit conditions. Different leaching fractions (LF = drainage volume/irrigation volume) and irrigation frequencies (IF) were imposed over a 119-day summer period in Las Vegas, Nevada, followed by a 71-day recovery period. Plots of tall fescue contained 120 cm deep × 51 cm diameter draining lysimeters. Irrigations were based on an evapotranspiration (ET) feedback system to establish LFs of +0.15, 0.00, -0.15, -0.25, and -0.40. Plots were irrigated on a daily or twice per week schedule. N was applied to subplots at a rate of 0, 12.2, or 24.4 kg·ha^-1 per month. As LF decreased, relative soil water in storage declined in a linear fashion (r ² = 0.97, P = 0.001). Storage depletions for the four lowest LFs at the end of 119 days of imposed water deficits were about 15%, 40%, 60%, and 70% compared to the +0.15 LF treatment. Canopy temperature, soil matric potential (Ψ_m), leaf xylem water potential (Ψ_LX), leaf stomatal conductance (g_s), clipping yield, color and cover ratings all statistically separated (P < 0.05) based on LF but not on IF. However, irrigation amount (I), ET, tissue moisture content and total Kjeldahl N (TKN) separated based on LF and IF with a significant LF by IF interaction for I (P < 0.05) and TKN (P < 0.001). An irrigation savings of 60.4 cm was realized during the 119-day water deficit period at the -0.40 LF. However, at the lower LFs, plant stress increased (all parameters) with color ratings declining below an acceptable value of 8.0. An Irrigation/Potential ET (I/ETo) threshold of 0.80 was determined for both color and cover. After a 71-day recovery period both color and cover returned to pre experimental values at the two higher N rates. Results of this experiment indicate that implementing a twice weekly irrigation strategy at a -0.15 LF on tall fescue during summer months in an arid environment would lead to savings of 37.5 cm of water while still maintaining acceptable color and cover ratings.

We investigated foliar damage to five landscape species sprinkler irrigated with either reuse water or one of five synthesized saline waters that contained elevated single salts mixed with Colorado River water, all having similar electrical conductivities. The experiment allowed us to compare the impact of elevated concentrations of Na, Mg, Ca, Cl, and SO₄ on an index of visual damage (IVD), tissue ion concentrations, and spectral reflectance. Waters containing elevated concentrations of MgCl₂ or NaCl caused greater foliar damage than did MgSO₄, Na₂SO₄, CaSO₄, or reuse water, as recorded in higher IVD values (p < 0.05). Privet and elm were damaged to a greater extent (higher IVD values) than were desert willow, guava and laurel (p < 0.05). Higher IVD values were recorded for all species irrigated with the MgCl₂ waters, with mortality recorded in privet. Tissue nutrient concentrations were correlated with the IVD values. In the case of guava, 61% of the variability in the IVD could be accounted for based on N, P and K (P < 0.01). On a treatment basis, the single salts added to the municipal water showed little correlation with the IVD values, except in the case of MgCl₂, where Mg was included in the regression equation (r ² = 0.82, P < 0.01, IVD↑ as S0₄↓, Mg and P↑). Eleven different spectral indices separated based on treatment and/or species (P < 0.05). In elm, 70% of the variability in the IVD could be accounted for by including Red Edge, Normalized Difference Vegetation Index (NDVI) and Water Band Index (WBI)/NDVI. A mixed response was observed to a post 30-day irrigation rinse in an attempt to reduce IVD values. Based on our results, care should be given to monitoring not only the EC (and osmotic potential) but also the ionic composition when saline waters are blended with other water sources, with the aim of minimizing the concentration of Mg, Cl, and Na.

Nineteen flowering landscape species were sprinkle irrigated with either reuse water or fresh water, with an additional treatment of reuse water plus shade (solar radiation reduced by 24%), for 113 days during late summer and early fall in southern Nevada. The species selected were common to mixed landscape areas on golf courses in southern Nevada transitioning to reuse water. An index of visual damage (IVD) was assessed, along with an assessment of flower production, canopy temperature, tissue ion analysis and spectral reflectance. The IVD values separated based on species (p < 0.001), treatment (p < 0.001) and by a species by treatment interaction (p < 0.001). Irrigating with reuse water plus shade reduced the IVD compared to the reuse without shade in 7 of the 19 species (p < 0.05). When IVD values were included for all species, 40% of the variation in the IVD values could be accounted for if N, B, Ca, Mg, Na, and Zn were included in the regression equation. Higher r ² values were obtained when individual species were isolated, with regression equations differing based on tissue ion combinations [e.g., ice plant (Mesembryanthemum crystallinum L.) r ² = 0.81 IVD↑, Na↓, Mn↑]. Three vegetation indices chlorophyll index (CHL), red/far red (R/FR) and water band index/normalized difference vegetation index (WBI/NDVI)) accounted for 51% of the variation in the IVD values. As much as 72% of the variation in vegetation indices could be accounted for based on tissue ion concentrations when separated based on treatment, with Na being the only common ion in all of the highest correlations. Flower production was highest in the reuse plus shade treatment in all 13 species flowering during the experimental period, with as much as 86% of the flower production variation driven by different tissue ion concentrations [purple cup (Nierembergia hippomanica), r ² = 0.86, flowers↑, Mn↑, Zn↓]. Nine of the nineteen species had acceptable levels of foliar damage (IVD < 2.0). We believe that if the spray irrigation can be minimized (bubblers/drip) and/or partial shade provided, through multi-story landscape designs, a more favorable response will be observed.

We compared transpiration estimates of three common desert landscape tree species using stem-flow gauges and lysimetry. Argentine mesquite (Prosopis alba Grisebach), desert willow [Chilopsis linearis (cav.) Sweet var. linearis], and southern live oak (Quercus virginiana Mill., seedling selection) were subjected to three irrigation regimes. Leaching fractions of +0.25, 0.00, and -0.25 were imposed for 2 years. During the summer of the second year, we conducted a comparative transpiration study. Trees growing in 190-liter plastic containers had a highly linear correlation (r = 0.98, P = 0.001) between transpiration estimated by stem-flow gauges and lysimetry. An average 18% error was measured between paired data (total runs of 14 to 72.5 hours) of stem-flow gauge and lysimetry transpiration estimates. However, a lower error was correlated significantly with longer run times (r = -0.37, P = 0.05). Based on field measurements taken in this experiment, run times would have to be >68 hours to maintain an associated error below 10%. Higher cumulative transpiration also was associated with longer run times (r = 0.80, P = 0.001). These results suggest that the stem-flow gauge can be used to estimate transpiration accurately to schedule irrigation for woody ornamental trees in an arid environment, provided that irrigation predictions are not based on short-term stem-flow gauge estimates (<68 hours).

Irrigation ponds on nine golf courses in southern Nevada were monitored for water quality over a 1600-day period. Three of the golf courses were fresh water courses, three were courses scheduled to transition to reuse water during the study period and three were long term users of reuse water. Salinity [electrical conductivity (EC)], NO ^– ₃-N, PO₄-P, pH, algal chlorophyll concentration, clarity, temperature, oxygen, and all major cations and anions were analyzed on a monthly basis. A selected fairway on each course was equipped with water meters to assess irrigation volumes on a bimonthly basis. Estimates of salt and NO ^– ₃-N loading on fairways were made by weighting irrigation volumes with concentrations of salt (assuming 700 mg·L^–1 per dS·m^–1) and NO ^– ₃-N measured in the irrigation ponds. Pond spectral reflectance measurements were obtained on a single monitoring day and correlated with water quality parameters. EC, temperature, NO ^– ₃-N, PO₄-P, algal chlorophyll concentration and clarity all demonstrated significant changes in all irrigation ponds that transitioned to reuse water (p < 0.05). Multiple regression analysis revealed that as much as 75% of the variability in pH in some irrigation ponds could be accounted for based on water quality parameters measured, with higher R² values associated with elevated HCO^– ₃ concentrations. Spectral reflectance (individual wave bands and spectral indices) was shown to be correlated with pH, clarity and algal chlorophyll concentration (R ² = 0.66^** to 0.82^***) with a well defined threshold relationship between clarity and the spectral index R705/R670. Average yearly NO ^– ₃-N loads on fairways averaged 8.5 kg·ha^–1·yr^–1 on fresh water courses, 86.5 kg·ha^–1·yr^–1 on transition courses and 209.8 kg·ha^–1·yr^–1 on long term reuse courses (all significantly different at p = 0.05). Average yearly salt loads on fairways averaged 11,959 kg·ha^–1·yr^–1 on fresh water courses, 14,675 kg·ha^–1·yr^–1 on transition courses and 27,445 kg·ha^–1·yr^–1 on long term reuse courses (long term significantly different at p = 0.05). Such results indicate that significant attention must be given to irrigation strategies used on reuse irrigated golf courses to properly manage for higher nitrogen and salt loads.