Due to water supply shortage and changing precipitation patterns, water for golf course irrigation is becoming increasingly limited. Irrigation restriction measures are likely to be implemented even in areas where supply is ample.
Water for golf course irrigation is becoming increasingly limited due to the shortage of fresh water supply and changes in precipitation patterns. Even in some areas where water supplies may be ample, water use restriction may be implemented in turfgrass irrigation due to economic concerns, particularly during peak demand season when water is costly. Inadequate water supply due to limited rainfall or irrigation is one of the most detrimental environmental factors causing loss of turf, which can have significant negative impacts on the playability and aesthetics of turfgrass.
Adequate water and uniform coverage are critical for the provision of quality turf surfaces.
Efficient use of water on golf courses is a prime concern in water-limited environments. As water availability becomes increasingly limited and more costly, water-saving programs in turfgrass management will become a necessity rather than an option in many areas.
Water use by turfgrasses is a function of plant growth characteristics and environmental conditions. Therefore, a sound, water-conservation program should include the integration of plant water requirements, environmental conditions and management practices. This paper discusses water use characteristics of turfgrass and several management practices promoting water conservation, particularly under drought and heat stress conditions.
Turfgrass Water Use and Requirements
Knowledge of water use rates of various grass species and factors affecting water use would help to develop efficient irrigation programs for water conservation. Water use in turfgrass typically is quantified by using evapotranspiration rate (ET), which refers to the loss of water from the soil through evaporation and from the plant through transpiration. Canopy ET rate can be estimated using tools such as lysimeters, weather station data, and evapotranspiration pans. Turfgrass ET rates vary among species and cultivars within a species. Typical water use rates range from 3 to 8 mm per day for cool-season turfgrasses and 2 to 5 mm per day for warm-season grasses under non-limiting soil moisture conditions.
Evapotranspiration rate is influenced by environmental conditions. Major factors include temperature, relative humidity, solar radiation, wind, water availability, and soil water holding capacity. Cultural practices such as irrigation and use of plant growth regulators (PGRs) have significant impact on water use rate and plant tolerance to environmental stresses such as drought and heat stress.
Reduced water requirements of Couch (RHS) compared to mixed cool season grasses on the left.
Efficient Irrigation Quantity and Frequency for Water Conservation
Optimal irrigation quantity and frequency may vary with turfgrass species/cultivars, environmental conditions, and cultural management regimes. However, studies have shown that deficit irrigation that provides irrigation water at amounts below maximum ET can be beneficial for water conservation without sacrificing turf quality. We conducted a field study on several bentgrass species under fairway conditions in New Jersey and found that replacement of 100% daily ET was not necessary for maintaining plant growth and physiological processes of creeping bentgrass, velvet bentgrass, and colonial bentgrass (DaCosta and Huang, 2006a). Deficit irrigation to replace 80% ET applied three times per week maintained best turf quality for all three species during spring, summer, and fall. Irrigation at 60% ET replacement was sufficient to maintain acceptable turf quality for velvet bentgrass during spring and summer months. Deficit irrigation at 40-80% ET also increased water use efficiency of bentgrass species (DaCosta and Huang, 2006b).
Research conducted by Jordan et al (2003) evaluating various cultivars of creeping bentgrass maintained under putting green conditions concluded that an irrigation frequency of every 4 days produced a larger and deeper root system, higher turf quality and shoot density when compared to treatments irrigated every 1 or 2 days.
Positive impact of infrequent irrigation on reducing water consumption and promoting drought tolerance has been previously reported in various other turfgrass species (Biran et al., 1981; Qian and Fry, 1996).
We also conducted a two-year project to examine irrigation frequencies that maintain quality turf with reduced use of water for creeping bentgrass, colonial bentgrass and velvet bentgrass under fairway management regimes (McCann and Huang, 2008a). Irrigating three times a week did not provide significantly better turf quality in all three species compared to plots irrigated once or two times per week during spring and fall. Thus, while environmental conditions may allow for watering once a week during cooler times, it is advisable to adjust irrigation frequency of bentgrass to twice a week during hot summer periods, particularly from mid-July to late August (equivalent to mid-January to late February in New Zealand). Watering at a 14-day interval resulted in poor turf quality for the majority of the season, and should not be considered a practical irrigation frequency for any of the evaluated species. Irrigation frequency had significant influence on ET rate in all three bentgrass species. Turf plots irrigated three times per week had the greatest rates of ET for all three grass species among the four different irrigation regimes. The 14-day irrigation interval had the lowest ET because of unhealthy turf with reduced water consumption. Considering the previous conclusion that adequate turf quality could be maintained when irrigated less frequently (once or 2 times per week), it may be possible to schedule irrigation programs that result in reduced water loss by ET and thus water savings.
Regulation of Turfgrass Water Use and Drought Tolerance Using Plant Growth Regulators
Plant growth regulators (PGRs) have been evaluated extensively for use in limiting turfgrass growth and reducing mowing requirements. Some plant growth regulators that contribute to the development of a short, compact turf have also been shown to reduce ET rates and improve turfgrass performance under drought stress or when irrigation is restricted.
One of the most widely used PGRs on fine turf is trinexapac-ethyl (TE) (commonly available as Moddus or Primo Max in New Zealand), including both warm- and cool-season turf on greens and fairways. This PGR is absorbed quickly by foliage. It slows cell elongation by inhibiting gibberellic acid production that controls cell elongation. TE has been traditionally used to suppress turf vertical growth, but research suggests that application of TE may reduce ET and improve drought tolerance in certain environmental conditions. We conducted a growth chamber study to examine effects of pre-conditioning creeping bentgrass with multiple application of TE (biweekly for three weeks) on drought responses. We found that pre-treatment with TE prolonged turfgrass survival of drought stress by suppressing shoot vertical growth prior to stress, and sustaining growth and photosynthetic activity during drought stress, as well as slowing soil water loss (McCann and Huang, 2008b). TE pre-treated creeping bentgrass maintained better leaf hydration through osmotic adjustment (accumulation of solutes for water retention). The positive effects of TE on turf performance under drought may not be related to changes in root growth, as the data on root growth are inconsistent. TE effects on turfgrass responses to drought stress may be related to reduced water use rate or ET, potentially resulting in lower irrigation requirements.
Field research investigating TE effects on turfgrass water use is limited, with most studies being conducted under controlled-environment conditions. A greenhouse study examining ET rate for tall fescue treated with TE at 370 mg L-1 showed an 11% reduction in ET over a six week period (Marcum and Jiang, 1997). In another greenhouse study, it was found that a mixed stand of Kentucky bluegrass and tall fescue treated with TE used 20% less water than the control within a four week period (King et al., 1997). Using lysimeters in a field study, Ervin and Koski (2001) reported that application of TE (0.27 kg a.i. ha-1) three times per year at 6-week intervals reduced weekly ET in Kentucky bluegrass in 5 out of a total of 34 weeks.
Current studies suggest that TE could be an effective tool for managing turf with limited irrigation. Pre-stress conditioning of turf with TE seems to be more effective than applying TE at the onset or during drought stress. TE can be applied to turf at reduced rates more frequently before a dry period is anticipated or prior to reducing irrigation. The influence of TE on turf water use rates seems to be related to a reduction in water demand due to the inhibition of vertical shoot growth and the production of smaller, more compact leaves. The production of smaller more compact leaves may reduce water lost through transpiration. However, more investigation is needed to reveal other possible explanations that may exist.
Water-Saving Irrigation Practice to Improve Drought and Heat Tolerance
Given the close association of water and heat stress, exposure of grasses to periodic drought stress by infrequent or deficit irrigation (drought preconditioning) before heat stress occurs would be expected to impact turfgrass tolerance to subsequent heat stress. Irrigation applications in the spring and fall, when maximum growth of shoots and roots occurs, may well dictate how well turf will perform in the summer. Infrequent or deficit irrigation that induces mild drought stress during spring could be used to enhance physiological hardiness to heat stress during summer.
Allowing surface soil drying between irrigation stimulates root growth into deeper soil profiles.
Saturated soil conditions following winter are not conducive to encouraging deep root systems.
Applying mild drought stresses in spring assist with encouraging deeper root systems.
This increases water use efficiency and could help grasses cope with surface-soil drought stress. Our research with several warm and cool-season grasses indicates that turf grasses are capable of maintaining favorable water status and acceptable quality even when soil surface layers (0-20 cm) are dry as long as water is available deeper in the profile.
Limiting irrigation or drought preconditioning can also improve heat tolerance. We conducted a study of Kentucky bluegrass exposed to two irrigation regimes. Grasses were watered daily regardless of plant needs (non-preconditioned) or watered when leaves wilted at volumetric soil moisture of 5% (about 15% of field capacity) (drought preconditioning) (Jiang and Huang, 2001). Preconditioned plants experienced two cycles of 14-day drying and watering before exposure to high temperature (35°C/30°C, day/night) in growth chambers. Drought-preconditioned Kentucky bluegrass maintained higher turf quality, canopy net photosynthesis rate and turgor potential than non-preconditioned plants during heat stress. Drought preconditioning-enhanced heat tolerance in Kentucky bluegrass is related to developing extensive deep roots and lowering osmotic potential (osmotic adjustment) of preconditioned plants. Osmotic adjustment associated with solute accumulation in plant cells is an important physiological mechanism of water retention and cell turgor maintenance under environmental stresses, particularly drought stress. Osmotic adjustment in Kentucky blue is associated with accumulation of ion solutes and water soluble carbohydrates. The K+, Ca2+, and water soluble sugar content were the major solutes contributing to osmotic adjustment in Kentucky bluegrass during heat stress.
Water conservation programs should be applied based on water use rate of plants, environmental conditions and cultural practices on a given site. Infrequent or deficit irrigation that induces mild drought stress during spring could be used to reduce water use, encourage root growth and enhance physiological hardiness to heat stress during summer. In cases where turf managers irrigate to excess during spring, reducing irrigation frequency prior to periods of anticipated high temperature stress may well have practical appreciation for improving heat tolerance. During summer, when evapotranspirational demand is high and rooting depth is reduced, frequent, light irrigation should be applied as needed. Finally, in the case of water use restriction, use of PGRs could help turfgrass better survive the period of drought stress.
Bingru at Taupo Golf Course in New Zealand last year.
Biran, I., B. Bravdo, I. Bushkin-Harav, and E. Rawitz. 1981. Water consumption and growth rate of 11 turfgrasses as affected by mowing height, irrigation frequency, and soil moisture, Agronomy Journal 73:85.
DaCosta, M. and B. Huang. 2006a. Minimum water requirements for creeping, colonial, and velvet bentgrass under fairway conditions. Crop Science 46:81-89.
DaCosta, M. and B. Huang. 2006a. Deficit irrigation effects on water use characteristics of bentgrass species. Crop Science 46:1779-1786.
Ervin, EH., and A.J. Koski. 2001. Trinexapac-ethyl effects on Kentucky bluegrass evapotranspiration. Crop Science 41: 247-250
Jiang, Y., and B. Huang. 2001. Osmotic adjustment associated with drought-preconditioning enhanced heat tolerance in Kentucky bluegrass. Crop Science 41:1168-1173.
Jordan, J.E., R.H. White, D.M. Vietor, T.C. Hale, J.C. Thomas and M.C. Engelke. 2003. Effect of irrigation frequency on turf quality, shoot density, and root length density of five bentgrass cultivars. Crop Science 43:282.
King, R.W., Blundell, C., Evans, L.T, Mander, L.N., Wood, T.J. 1997. Modified gibberellins retard growth of cool-season turfgrasses. Crop Science 37:1878–1883.
Marcum, K.B. and Jiang, H. 1997. Effects of plant growth regulators on tall fescue rooting and water use. Journal of Turfgrass Management 2:13-27.
McCann, S., and B. Huang. 2008a. How much water can be saved by practicing deficit irrigation? The Greenerside. 32(2):7-11.
McCann, S., and B. Huang. 2008b. Drought responses of Kentucky bluegrass and creeping bentgrass as affected by abscisic acid and trinexapac-ethyl. Journal of American Horticultural. Science 133:20-26.
Qian, Y., and J.D. Fry. 1996. Irrigation frequency affects zoysiagrass rooting and plant water status. HortScience 31:234-237.
Ralph Geiger Chair Professor
Department of Plant Biology and Pathology