Growth response of eight tropical turfgrass species to salinity

Irrigation seawater of different salinity levels (0, 24, 48 and 72 dSm -1 ) were applied to experimental plants grown in a plastic pots filled with a mixture of sand and peat (9:1). The results were analyzed using SAS and treatment means were compared using LSD Test. The results indicated that Paspalum vaginatum (seashore paspalum) (SP), Zoysia matrella (manilagrass) (MG), Pasplaum vaginatum local (SPL), Cynodon dactylon (common bermuda) (CB), Cynodon dactylon (bermuda greenless park) (GLP), Eremochloa ophiuroides (centipede) (CP), Axonopus compressus (cow grass) (CG) and Axonopus affinis (narrowleaf carpet grass) (NCG) experienced a 50% shoot growth reduction at the EC of 39.8, 36.5, 26.1, 25.9, 21.7, 22.4, 17.0 and 18.3 dSm -1 , respectively, and a 50% root growth reduction at the EC of 49.4, 42.1, 29.9, 29.7, 26.0 24.8, 18.8 and 20.0 dSm -1 , respectively. The ranking for salinity tolerance of selected grasses was SP>MG>SPL>CB>GLP>CP>NCG>CG. The results indicate the importance of the selection of turfgrass varieties according to the soil salinity and seawater salinity levels to be used for irrigation.


INTRODUCTION
Soil salinity is considered as one of the major factors that reduce plant growth in many regions of the world.Consequently, secondary water sources are increasingly being used to irrigate large turf facilities (Arizona Department of Water Resources, 1995;California State Water Resources control board, 1993).Seawater intrusion in the coastal states (McCarty and Dudeck, 1993;Murdoch, 1987) has added to the salinity problems in turfgrass culture.Sodium chloride (NaCl) is the predominant component contributing to salinity in soils (Jungklang et al., 2003).Therefore, the need for salt tolerant turfgrasses has increased (Harivandi et al., 1992).Salt tolerant turfgrasses are becoming essential in many areas of the world including Malaysia because of salt accumulation on soil, restrictions on groundwater use and saltwater intrusion into groundwater (Hixson et al., 2004).Physiological *Corresponding author.Email: mkuddin07@yahoo.comresponses to salinity include growth suppression and lowered osmotic potential (Marcum, 2006).Salt tolerant plants have the ability to minimize these detrimental effects by producing a series of morphological, physiological and biochemical processes (Jacoby, 1999).
A new generation of salt-tolerant turf varieties might allow landscape development in saline environments and might be ideal in such environments where salt water spray is a problem, or where limited or no fresh water is available for irrigation.Turfgrass developments in these areas are often required to use brackish water from affected wells or other secondary sources.To our knowledge, there are no published studies that have investigated the salt water tolerance among turfgrass species in Malaysia.The proper utilization of highly salt tolerance turfgrass species will give so much benefit to turfgrass area in

Malaysia.
The objective of this study was to determine the relative salt tolerance and growth response of warm season turfgrass species grown on sand culture to salinity.

MATERIALS AND METHODS
The experiment was conducted in the glasshouse of Faculty of Agriculture at Universiti Putra Malaysia under sand culture system.Eight turfgrass (Table 1) species were planted in plastic pot filled with a mix of 9 washed river sand: 1 peat moss (v/v).The soil was sandy with pH 5.23, EC 0.3 dSm -1 , Organic Carbon 0.69%, sand 97.93%, silt 1.89% and clay 0%.The diameter of plastic pots was 14 cm with 15 cm depth.The average day temperature and light intensity of glass-house were 28.5-39.5 0 C and 1500 -20400 lux respectively (Figure 1).The temperature was measured by a thermometer and light intensity was measured by heavy duty light meter (Extech ® model 407026).All pots were fertilized with green NPK (15:15:15) @ 0.5 kg / 100 m 2 / month and applied forts nightly.
The native soil on the grasses were washed from the sod and then sods were transplanted into the plastic pots and grown for 8 weeks with non-saline irrigation water in order to achieve full establishment.Grasses were clipped by scissors weekly throughout the experiment at the cutting height of 15 mm for course leaf and 5 mm for narrow leaf.The required quantity of sea water was collected from Morib Beach, Selangor, Malaysia.The EC was 48 dSm -1 .Four salt water concentrations namely T1 = 0, T2 = 24, T3 = 48 and T4 = 72 dSm -1 were applied in this study.The salinity level was measured by EC meter (HANNA ® model HI 8733).Untreated checks (T1) were irrigated with distilled water.Seawater was diluted 50% by adding distilled water for treatment T2.NaCl was added to seawater for T4 to obtain the salty water level of 72 dSm -1 .To avoid salinity shock, salinity levels were gradually increased by daily increments of 8 dSm -1 in all treatments until the final salinity levels were achieved.After the targeted salinity levels were achieved, the irrigation water was applied on daily basis for a period of four weeks.The amount of water applied were 200 ml per pot.Data were collected on leaf firing, turf quality, shoot growth and root growth.Leaf firing was estimated as the total percentage of chlorotic leaf area, with 0% corresponding to no leaf firing, and 100% as totally brown leaves.Turf quality was estimated based on a scale of 1 -9, with 9 as green, dense and uniform turf, and 1 as thin and completely brown turf (Alshammary et al., 2003).At the end of the experiment shoots were harvested and roots were clipped.Both shoots and roots were washed with deioniozed water and dried at 70 0 C for 72 h to determine root and shoot dry weight.
(RCBD) with five replications.The experimental data were analyzed The experimental design was a Randomized Complete Block Design by analysis of variance (SAS Institute, 2004).Treatment means were separated by LSD test.Regression analysis was used to determine the relationship between each variable and the salinity level.Growth measurements (shoot weight and root weight) were expressed as percentages, relative to control and relative growth values are calculated as follows: (Dry weight of salinized treatment value ÷ dry weight of control treatment value) ×100.

Axonopus compressus (CG) and
A. affinis (NCG) experienced a 50% shoot growth reduction at 39.8, 36.5, 26.1, 25.9, 21.7, 22.4, 17.0 and 18.3 dSm -1 respectively (Figure 2).Relative shoot growth of turf grass P. vaginatum (SP) was the highest, followed by Z. matrella (MG) while relative shoot growth for A. compressus (CG) and A. affinis (NCG) reduced drastically were at 24 dSm -1 salinity level.However, relative shoot growth of P. vaginatum (SP) dramatically decreased at 48 dSm -1 salinity which is even lower than that of P. vaginatum local (SPL) (Figure 2).Meanwhile relative shoot growth was recorded as the highest for P. vaginatum (SP) at 24 dSm -1 followed by Z. matrella (MG) while it was recorded the lowest for A. compressus (CG) (Figure 2).Relative shoot growth was the lowest for Z. matrella (MG) while P. vaginatum local (SPL) and E. ophiuroides (CP) were low statistically identical in their growth at 48 dSm -1 . Relative shoot growth was signifi-cantly reduced in A. compressus (CG) and A. affinis (NCG).Similar trend was observed at the highest salinity level of 72 dSm -1 .

Turf quality
Turf quality under salt stress as indicated by visual ratings is presented in Figure 5. Turf quality decreased with increasing salinity level.Turf quality decreased severely in A. affinis (NCG) and A. compressus (CG) while P. vaginatum (SP) and Z. matrella (MG) exhibited the best turf quality among the entries at all salinity levels (Figure 5).Other four species including P. vaginatum local (SPL), C. dactylon (GLP), E. ophiuroides (CP) C. dactylon (CB) were intermediate in their quality ranking.At 24 dSm -1 turf quality was unaffected in P. vaginatum (SP) (9) but was slightly decreased in Z. matrella (8) (Figure 5).However, turf quality was drastically reduced in A. affinis (NCG) (2) and A. compressus (CG) (2) but was moderate (4 -8) in , turf quality was decreased significantly in all turfgrass tested in this experiment.

DISCUSSION
Growth parameters, such as shoot growth (Francois, 1988;Marcum and Murdoch, 1990), root mass (Marcum and Kopec, 1997) and turf quality (Dean et al., 1996;Marcum and Kopec, 1997;Marcum, 1999) have been reported to be excellent criteria to determine salinity tolerance among turfgrasses.Assesment of salinity tolerance using percent leaf firing has been reported in previous studies (Marcum, 1999;Lee et al., 2004b).Leaf firing can be included in salinity assessment as one criterion because leaf firing is easily measured.Relative shoot growth (as a percent of control) decreased with increasing salinity in all species.A tolerance criteria commonly used in salinity studies is the salinity level that result in 50% shoots dry weight reduction relative to the control (Lee et al., 2004a;Mass, 1986).In terms of interactions among soil, plant and surrounding environmental factors during field evaluation, relative yield response is beneficial where comparing salinity tolerance across crop species and environments.
In our studies, based on data on growth parameters (relative shoot growth, 50% shoot growth reduction, leaf firing and turf quality) the salinity tolerance ranking of selected grasses from the most tolerant to less tolerant was P. vaginatum (SP), Z. matrella (MG), P. vaginatum local (SPL), C. dcatylon (CB), C. dcatylon (GLP), E. ophiuroides (CP), A. affinis (NCG) and A. compressus (CG).Shoot growth rates of P. vaginatum and Z. matrella were higher than other grasses at all salinity levels.Marcum and Murdoch (1994) reported that relative shoot growth (as a percent of control) was reduced by 50% at the salinity level of 36.4 dSm -1 NaCl in P. vaginatum and 35.9 dSm -1 in Z. matrella.Lee et al., (2005) also reported that seashore paspalum were able to maintain 50% of shoot dry weight relative to the control up to 37 dSm -1 .Shoot growth and turf quality of turfgrass were reduced as the salinity level of irrigation water increased (Peacock and Dudeck, 1985;Dean et al., 1996).
Based on this result P. vaginatum (SP) and Z. matrella (MG) were the two most salt tolerant turdgrass species.P. vaginatum (SP) is one of the most salt tolerant turfgrass cultivars; even seawater with 54 dSm -1 can be used for irrigation (Duncan and Carrow, 2000).Bermudagrass is listed as salt tolerant by Carrow and Duncan (1998).In our study P. vaginatum local (SPL) and C. dcatylon (CB) were more salt tolerant than A. compressus (CG), A. affinis (NCG), C. dcatylon (GLP) and E. ophiuroides (CP).Dudeck et al. (1983) reported that common bermuda is less salt tolerant than Tifgreen and Tifdwarf.Uddin et al. 5805 Growth limitation at high salinity may be due to depletion of energy that is needed for growth and the loss of turgor (Marcum, 2006).Root growth stimulation under saline condition has been observed in bermuda grass (Dudeck et al., 1983) and seashore paspalum (Dudeck and Peacock, 1993).

Conclusion
The relative salinity tolerance of turfgrass root growth, shoot growth and leaf firing were closely associated with salinity tolerance of the grasses.The different species of grasses were grouped for salinity tolerance on the basis of 50% shoot and root growth of reduction, leaf firing and turf quality with increasing salinity.The first groups was the most tolerant species including P. vaginatum (SP) and Z. matrella (MG) which were able to tolerant high levels of salinity between 36.5 to 49.4 dSm -1 .In the second group were the moderate tolerant species including P. vaginatum local (SPL) and C. dactylon (CB) which were able to tolerate salinity level between 25.9 to 29.9 dSm -1 , while in the lowest tolerant performance group were C. dactylon (GLP), E. ophiuroides (CP) A. compressus (CG) and A. affinis (NCG) varieties, which were affected at salinity level of between 17.0 and 26.0 dS m -1 .

Figure 1 .
Figure 1.Temperature and light intensity fluctuation in the glass house.

Table 1 .
Scientific name, common name and subfamily of turfgrass species.