Final Report for Horticulture Australia Ltd Project TU04001 (30 th May 2008)

Transcription

1 Final Report for Horticulture Australia Ltd Project TU04001 (30 th May 2008) The Kikuyu Research Project: Nitrogen Fertiliser Regimes, Water Use, and Renovation Dr Louise Barton Dr Tim Colmer School of Plant Biology Faculty of Natural & Agricultural Sciences The University of Western Australia

2 Horticulture Australia Ltd Project Number TU Louise Barton Dr Louise Barton, School of Plant Biology (M084), Faculty of Natural & Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia. Fax: Other Key Personnel Associate Professor Tim Colmer, School of Plant Biology (M084), Faculty of Natural & Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia. Fax: Mr George Wan, School of Plant Biology (M084), Faculty of Natural & Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia. Fax: Mrs Renee Buck, School of Plant Biology (M084), Faculty of Natural & Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia. Fax: Purpose of the Report Australian turfgrass managers are seeking more cost efficient and environmentally acceptable approaches to manage turfgrass. Fertilising and controlling mat accumulation both contribute to the cost of managing turfgrass, and depending on the approach taken, can also pose a risk to the environment. Our understanding of turfgrass management practices and their effects on the environment is based mainly on data collected from cool-season turfgrasses studied in the Northern Hemisphere. Therefore, the overall objective of the Kikuyu Research Project was to optimise nitrogen fertiliser and mat control management practices for Kikuyu turfgrass under southern-australian conditions. The project aims included: i) optimising fertiliser management so that nitrogen leaching is minimised while maintaining turfgrass growth and quality; ii) evaluating the effect of nitrogen fertiliser management on turfgrass water use; and iii) investigating techniques for controlling thatch/mat accumulation in Kikuyu turfgrass. Acknowledgements This project has been facilitated by HAL in partnership with the turf industry. It was funded by voluntary contributions from the Parks and Leisure Association of Australia, CSBP Ltd, Organic 2000, Turf Grass Association of Australia (WA), WA Golf Course Superintendents Association, Baileys Fertilisers, Turf Master Facility Management, Turf Growers Association of Western Australia, Lawn Doctor, Micro Control Engineering, and the Water Corporation. The Australian Government provides matched funding for all HAL's R&D activities. Date 30 th May 2008 Any recommendations contained in this publication do not necessarily represent current Horticulture Australia policy. No person should act on the basis of the contents of this publication, whether as to matters of fact or opinion or other content, without first obtaining specific, independent professional advice in respect of the matters set out in this publication.

3 CONTENTS 1. Media Summary Technical Summary General Introduction Effects of Nitrogen Fertiliser Regimes on Kikuyu Growth and Nitrogen Leaching Introduction Materials and Methods Results Discussion Effects of Nitrogen Fertiliser Rate on Kikuyu Water Use Introduction Materials and Methods Results Discussion Cultural Controls on Thatch and Mat and Effects on Kikuyu Growth and Quality Introduction Materials and Methods Results Discussion Technology Transfer Publications in Industry Journals Industry Seminars, Workshops and Field Days The University of Western Australia Turf Research Seminar Day Scientific Papers and Presentations Guidelines Recommendations Scientific and Industry Fertiliser Regimes for Maintaining Turfgrass and Minimising Leaching Nitrogen Fertiliser Regimes for Minimising Turfgrass Water Use Techniques for Minimising Organic Matter Accumulation Acknowledgements Bibliography of Literature Cited

4 1. MEDIA SUMMARY Turfgrass is often perceived to contribute to nitrogen leaching and inefficient water use. Management strategies for overcoming these issues based on scientific data from Australian turfgrass management systems was lacking. The University of Western Australia investigated approaches for minimising the environmental impact of turfgrass management. Key questions included: How much, and how often, should nitrogen fertiliser be applied to maintain turfgrass and minimise nitrogen leaching? How much water does turfgrass (Kikuyu) use, and does it vary with the amount of nitrogen fertiliser applied? What techniques decrease thatch-mat in turfgrass, and does it depend on the amount of thatch-mat already present? Nitrogen leaching from established turfgrass can be minimised by applying moderate amounts of nitrogen fertiliser (< 150 kg N ha -1 yr -1 ), and ensuring irrigation water does not move beyond the rooting zone. Increasing the frequency of applications (whilst maintaining the annual application rate) beyond two per year is unlikely to decrease nitrogen leaching further; however, it may improve the consistency of turfgrass growth and colour. Water use by Kikuyu turfgrass was equivalent to 69 75% of net evaporation during summer. Increasing nitrogen fertiliser rates will increase turfgrass water use. Choosing warm-season turfgrasses over cool-season turfgrasses, and matching nitrogen fertiliser rates to growth, will minimise turfgrass water use in Mediterranean-type climates. Recommended renovation techniques will vary depending on the initial thatch-mat content of the turfgrass. Scarifying or topdressing (with sand) newly established turfgrass, and topdressing older turfgrass with pre-existing mat, prevents excessive accumulation of organic matter. 2

5 2. TECHNICAL SUMMARY The overall objective of the Kikuyu Research Project was to optimise N fertiliser and thatchmat control management practices for Kikuyu turfgrass under southern-australian conditions. The project aims included: optimising N fertiliser management, so that N leaching is minimised while maintaining turfgrass growth and quality; evaluating the effect of N fertiliser rates on turfgrass water use; and investigating techniques for controlling thatch-mat accumulation in Kikuyu turfgrass of two ages (i.e., 20 year old turfgrass that includes 50 mm mat, 20 week old turfgrass). The effects of N fertiliser regimes on turfgrass quality and N leaching from Kikuyu turfgrass (Pennisetum clandestinum) were field-evaluated for 24 months. Treatments included two turfgrass ages, three N application rates (50, 100 or 150 kg N ha -1 yr -1 ) and three application frequencies (every 4 weeks, 4 applications per year, 2 applications per year); and included turfgrass plots that received no N fertiliser. Once established, turfgrass plots were irrigated by replacing 60% net evaporation every 2 nd day during the growing season. Nitrogen leaching, measured using soil lysimeters inserted in turfgrass field plots (10 m 2 ), ranged from 33 to 68 kg N ha -1 after 24 months, and did not vary with turfgrass age nor fertiliser regime. Greatest N losses occurred during turfgrass establishment, with up to 50% as organic-n. The quality of the older turfgrass was maintained using less N fertiliser than the younger turfgrass, while increasing N application frequency improved the consistency of turfgrass growth and colour. The effect of N fertiliser rate on Kikuyu turfgrass water use (i.e. evapotranspiration) was evaluated during two summers. Water use was measured using weighing lysimeters (205 mm in diameter by 625 mm in length) inserted in turfgrass field plots (10 m 2 ). The experiment was a randomised plot design with three replicates. Treatments included two turfgrass ages and three N application rates (0, 50 or 150 kg N ha -1 yr -1 ), and plots were irrigated by replacing 60% of net evaporation every 2 nd day. Evapotranspiration ranged from 2.8 to 7.5 mm day -1 (or 56 81% of net evaporation), and varied with daily evaporative demand, turfgrass age, and N fertiliser rate. The older turfgrass used more water than the younger turfgrass during both summers; while increasing the N application rate also increased evapotranspiration for both turfgrass types (younger turfgrass only in the second summer). Evapotranspiration was positively correlated with turfgrass growth (r 2 =0.74) and transpiring leaf area (r 2 =0.78). All older turfgrass treatments, and the younger turfgrass receiving 150 kg N ha -1 yr -1, had adequate growth, colour and leaf N concentrations. Optimising N fertiliser applications such that turfgrass quality is maintained, but without excessive evapotranspiration, is an approach for decreasing water consumption by turfgrass. The effectiveness of mechanical and topdressing techniques to reduce the accumulation of thatch and mat in Kikuyu turfgrass was field-evaluated for 24 months. Treatments included two turfgrass ages, and five renovation techniques (none, scarifying, coring, topdressing with sand, coring + topdressing). Annual scarifying or bi-annual topdressing a younger turfgrass with low initial soil organic matter (OM) content (in surface 50 mm) were most successful at restricting the accumulation of soil OM; whereas bi-annual topdressing most rapidly decreased soil OM in the older turfgrass with a high initial OM content. Turfgrass quality was maintained by all techniques, although scarifying decreased mower scalping. We recommend the turfgrass industry utilise approaches where by N fertiliser applications match turfgrass requirements. Efficient fertiliser management will benefit turfgrass quality, minimise the risk of N leaching, and reduce water consumption. 3

6 3. GENERAL INTRODUCTION Turfgrass is common in our urban landscapes and plays a part in the daily lives of almost all Australians. Turfgrass is used for a variety of purposes including home lawns, street verges, public parks, and as a surface for many sports. In addition to these aesthetic and recreational benefits, turfgrass also provides environmental benefits such as heat dissipation and control of soil erosion and dust (Busey and Parker 1992). Turfgrass farming has become an important horticultural industry in Australia, and turfgrass management businesses employ thousands of people across Australia. Nowadays people are more aware of the detrimental effects on the environment of improper use of N fertilisers. Poor N fertiliser management can cause N leaching, and increase the emissions of greenhouse and ozone depleting gases (i.e., N 2 O, NO x, and NH 3 ). Nitrogen leaching is problematic as it can degrade aquatic systems and compromise water used for drinking, industry and recreation (Smith 1998). Turfgrass generally requires regular irrigation and fertiliser applications, and is often perceived to be a source of N leaching, especially from coarse textured soils. Fuelled by the rising incidence of algal blooms in rivers of some of Australia s capital cities, the contribution of turfgrass systems to N leaching is increasingly being scrutinised by communities and environmental regulators. Yet, turfgrass areas need not pose a risk to the environment if appropriate management strategies are undertaken. Overseas and Australian studies have shown irrigation scheduling that does not cause water to move beyond the rooting zone will successfully decrease the amount of N leached from turfgrass, without being detrimental to turfgrass growth or quality (Barton and Colmer 2006; Barton et al. 2006b). Applying N fertilisers at rates and frequencies that match turfgrass requirements can also decrease N leaching from established turfgrass (Snyder et al. 1984). Although irrigation rates that minimise N leaching from coarse textured soils are reasonably well understood, N fertiliser regimes (i.e., rates and timing of applications) that minimises N leaching from established turfgrass types commonly grown under Australian conditions (e.g., warm-season genotypes) are not well defined. Southern Australia is expected to experience a decrease in water resources due to changing climate (Kundzewicz et al. 2007). For example, south-western Australia has experienced a 20% reduction in winter rainfall since the late 1960s (Allan and Haylock 1993). Not surprisingly, the pressure on Australian turfgrass managers to justify water use has also increased, and the need to develop water efficient turfgrass management practices has intensified. Turfgrass water use, or evapotranspiration (ET), varies depending upon a number of factors, including: climate, quantity and quality of the water applied, and cultural practices (Kneebone et al. 1992). Promoting turfgrass management practices that decrease water use requires not only an understanding of how the proposed practices will affect water consumption, but also knowledge of how these strategies will impact on turfgrass quality. Although manipulating N fertiliser rate, mowing height and frequency, and soil water availability have been shown to decrease turfgrass ET (Biran et al. 1981; Ebdon et al. 1999; Feldhake et al. 1983; Fry and Butler 1989; Mantell 1966; Shearman and Beard 1973), these studies have not always included quantitative information on how these factors also affect turfgrass quality. Furthermore, most studies investigating the influence of cultural practices on turfgrass water use have been conducted in North America, and the universal applicability of these findings is unclear. As a consequence, it is often not clear to what extent water savings can be made by altering turfgrass management practices in Australia, without adversely affecting turfgrass quality. 4

7 Nitrogen fertiliser management can also influence the amount of clippings produced, and the accumulation of thatch. Excessive turfgrass growth is undesirable as it increases maintenance costs (e.g., mowing, thatch removal) and disposal costs (i.e., green wastes). Thatch accumulation is also undesirable because it causes problems with turfgrass growth including: localised dry spots, chlorosis, proneness to scalping, decreased heat and drought hardiness, and decreased water infiltration rates (Waddington 1992). Various practices have been proposed for managing thatch development including optimising N fertiliser management and topdressing turfgrass with sand (Carrow et al. 1987; Waddington 1992). These methods are considered to be more cost effective and less disruptive than the mechanical methods often used to control and remove thatch (e.g., coring and vertical mowing). The effectiveness of these techniques to manage thatch accumulation under Australian conditions is not clear. For example, overseas studies show that the effects of N fertiliser programs on thatch accumulation are often confounded due to lower soil ph (associated with increased N application rates) decreasing thatch decomposition rates (Waddington 1992). With increasing landfill restrictions on wastes and efforts to minimise resource inputs to turfgrass systems, further information is required on how N fertiliser management and thatch control methods influence clipping and thatch production of warm-season grasses grown under Australian conditions. Australian turfgrass managers are seeking more cost efficient and environmentally acceptable approaches to managing turfgrass. Research is required to provide turfgrass managers with alternative fertiliser and thatch control regimes. The overall objective of the Kikuyu Project was to optimise turfgrass management practices for Kikuyu such that turfgrass quality is maximised without compromising the receiving environment. Specifically the project aims were to: i) optimise N fertiliser management so that N leaching is minimised while maintaining turfgrass growth and quality (Section 4); ii) evaluate the effect of N fertiliser rates on turfgrass water use (Section 5); and iii) investigate techniques for controlling thatchmat accumulation in Kikuyu turfgrass (Section 6). 5

8 4. EFFECTS OF NITROGEN FERTILISER REGIMES ON KIKUYU GROWTH AND NITROGEN LEACHING 4.1 Introduction Turfgrass generally requires regular irrigation and fertiliser applications, and is often perceived to be a source of N leaching, especially on coarse-textured soils. Nitrogen leaching is problematic as it can degrade surface- and ground-waters resulting in eutrophication and non-potable water supplies (Carpenter et al. 1998; OECD 1982; Smith 1998). Managing N leaching is considered difficult because losses are often intermittent, and linked with seasonal land management activities or irregular events such as rainfall or soil disturbance. However, turfgrass areas need not pose a risk to the environment if appropriate irrigation and fertiliser management strategies are undertaken (Barton and Colmer 2006). Leaching is best minimised by ensuring applied N is maintained within the root zone, and is applied at a rate that the soil-turfgrass system is able to assimilate or utilise (Carpenter et al. 1998; Powlson 1988). Efficient irrigation management is critical for decreasing the risk of N leaching. Irrigation scheduling that does not cause water to move beyond the root zone decreased the amounts of nitrate and ammonium leached from established turfgrass in temperate climates, without being detrimental to turfgrass growth or quality (Barton and Colmer 2006). The amount of water applied needs to match turfgrass requirements, but rates and frequencies should be chosen to avoid preferential flow. Applying N fertilisers at rates that match turfgrass requirements is also expected to decrease N leaching from established turfgrass (Barton and Colmer 2006; Petrovic 1990), although the benefits may be less marked under optimised irrigation regimes (Barton et al. 2006b; Snyder et al. 1984). Applying water-soluble N fertilisers sparingly and frequently is often recommended for minimising N leaching from turfgrass; yet, optimal frequencies have rarely been investigated for an extended period. Snyder et al. (1984) demonstrated that applying ammonium nitrate weekly (via fertigation), rather than bi-monthly, decreased N leaching from 17% to 2.5% of the N applied to established bermudagrass with irrigation scheduled using soil moisture sensors; however, the study was only conducted for six months during a single growing season. In addition, our understanding of turfgrass management practices and their effects on the environment is based mainly on data from cool-season turfgrasses grown in the Northern Hemisphere (Barton and Colmer 2006). We hypothesise that N leaching under turfgrass grown on sandy soils under conservative irrigation scheduling will be further decreased, and turfgrass quality maintained, by increasing the frequency of N application for a given annual N amount. Consequently the objective of our 24 month study was to investigate the effects of N fertiliser rate and application frequency on growth, quality, and N leaching from Kikuyu turfgrass (Pennisetum clandestinum) of two ages grown on a free-draining sandy soil in a Mediterranean-type climate. 6

9 4.2 Materials and Methods Soil and site Kikuyu (Pennisetum clandestinum) turfgrass plots were established at The University of Western Australia s Turf Research Facility located at Shenton Park (31 56 S, E), approximately 8 km west of Perth city. Perth has a Mediterranean-type climate, with an annual rainfall of 859 mm, which mainly falls during the winter months, a mean annual maximum temperature of 24.5 C and a mean annual minimum temperature of 12.8 C (Commonwealth Bureau of Meteorology, The soil at the experimental site is known locally as Karrakatta Sand (McArthur and Bettenay 1960) (Dystric Xeropsamments) (USDA 1992) and was cleared of vegetation (Banskia woodland) in The soil is free-draining and has a low chemical fertility and low biological activity. The surface soil (0 150 mm) has a ph of 4.8 (1:5 soil : 0.01 M CaCl 2 extract), electrical conductivity of 0.02 ds m -1 (1:5 soil : water extract), cation exchange capacity of 3.22 cmol (+) kg -1, C concentration of 9.3 mg g -1 and N concentration of 0.4 mg g -1. The subsurface soil (> mm) has a ph of 5.6, electrical conductivity of 0.01 ds m -1, cation exchange capacity of 1.33 cmol (+) kg -1, C concentration of 0.4 mg g -1 and N concentration of 0.2 mg g - 1. The surface soil contains 92% coarse sand, 2% fine sand, 2% silt and 4% clay (Pathan et al. 2003). The site included a variable-speed travelling irrigator with a fixed-boom (Short and Colmer 2007) coupled with a weather station (WeatherMaster 2000, Environdata Australia), that enabled irrigation water to be applied evenly and at known rates. The amounts of water applied to the turfgrass were determined by the velocity of the irrigator. The irrigator travelled along a 72 m rail track propelled by a diesel motor directly coupled to hydraulic pumps. Water was pumped from a central channel onto the experimental blocks via four separate 9.5 m sections of a boom; each section was individually controlled by solenoid valves actuated at selected times by a microprocessor unit. The microprocessor unit also had the ability to accelerate or decelerate the irrigator and to monitor engine function, water flow and pressure, and the position of the irrigator. The median daily efficiency of discharge value ([actual irrigation depth/programmed irrigation depth] x 100) was 97% (data not shown). A weather station was installed on the experimental site to measure climatic parameters, plus calculate daily net evaporation for use by the irrigator program. Rainfall was measured using a 203 mm diameter automated tipping rain gauge with a resolution of 0.2 mm. Air temperature was measured using a semi-conductor junction with an amplifier (resolution of 0.1 C), relative humidity using a capacitive humidity sensor (resolution of 0.1%), solar radiation using a silicon pyranometer (resolution of 15 W m -2 ), and wind speed and direction using an anemometer (resolution of 0.1 km h -1 ); with sensors located at a height of m above the ground. Net evaporation was calculated by the weather station by subtracting rainfall from evaporation that was calculated using a modified Penman equation (Doorenbos and Pruitt 1977) Experimental design and approach The experimental design was completely randomised, consisting of two turfgrass ages by three N fertiliser rates by three frequencies of application, by three replicates. The two turfgrass ages were either plots (10 m 2 ) established from 20 week old turfgrass ( younger turfgrass) or plots established from 20 year old turfgrass ( older turfgrass). The younger turfgrass was newly grown sod, cut to a depth of 15 mm; while the older turfgrass was cut 7

10 from a golf course fairway to a depth of 50 mm so as to include a mat layer of high organic matter content (OM, 36%). The N fertiliser rates were 50, 100 or 150 kg N ha -1 yr -1 as (NH 4 ) 2 SO 4. Each annual N fertiliser rate was evenly split so that plots were fertilised every 4 weeks, 4 times per year (2 applications in spring and 2 in autumn) or 2 times per year (1 application in spring and 1 in autumn). Each turfgrass age also included three turfgrass plots that did not receive fertiliser. Turfgrass plots were planted with sod on 19 Jan. 2005, with lysimeters for measuring N leaching installed in each plot at the same time. The lysimeters consisted of polyvinyl chloride (PVC) cylinders (250 mm in diameter by 980 mm in length), filled with air-dried soil. The lysimeters contained turfgrass roll (15 mm depth, younger turfgrass; 50 mm depth, older turfgrass) overlaying a surface soil (100 mm in depth), followed by a subsurface soil (800 mm in depth), a polyester filter, and a layer of coarse quartz stones (60 mm depth, younger turfgrass; 20 mm, depth, older turfgrass). The soil used came from the same site as the plots, and surface and subsurface soil properties are listed above. The base of each lysimeter funnelled leachate to a central exit point from which leachate was collected into a 4.5 L plastic container. Each lysimeter was inserted into a metal sleeve (300 mm in diameter by 1000 mm in length) previously dug into the field plots. This enabled the lysimeters to be lifted from the ground using a winch. The surface of each lysimeter was flush with the surface of the plots; however, the surface of the lysimeter turfgrass was 5 mm below the surface of the lysimeter so as to avoid water and nutrient run-off. Leachate was collected by hand-pumping it from each lysimeter via a 4 mm nylon pneumatic tube. Turfgrass in lysimeters was fertilised by hand at the same time as the turfgrass plots, with the fertilisers applied to the lysimeters weighed separately to ensure that each lysimeter received the correct amount of fertiliser Irrigation and fertiliser applications For the first six weeks after planting, plots were irrigated at 100% replacement of net evaporation, and split so water was applied up to three times a day. After six weeks, the irrigation rate was decreased in steps so that after eight weeks the plots were irrigated at 60% replacement of net evaporation, and this replacement of cumulative net evaporation for two days was given every second day; which is sufficient to maintain younger turfgrass in southwestern Australia (Short 2002). In general, irrigation occurred every second morning from October to May; and then occasionally at other times of the year if weekly net evaporation exceeded 5 mm. To avoid lateral movement of water and fertiliser from plots, irrigation never exceeded 5 mm in any single pass of the irrigator. When the irrigation requirement exceeded 5 mm, the irrigator was programmed to make additional passes until the daily target was met. Fertiliser was applied by hand with a subsample of the fertiliser collected at each application date and analysed for total N using a CHN analyser (LECO CHN 1000; MI, USA). After two years, the amount of N applied did not differ from the expected N application by more than 0.5%. Each spring, turfgrass samples were collected and analysed for a variety of elements essential for turfgrass growth. Dried samples were ground and digested in nitric acid before being analysed for a series of elements (K, P, S, Ca, Mg, Mn, Cu, Zn, Fe, B) using inductively coupled plasma-atomic emission spectroscopy (ICP-AES) (McQuaker et al. 1979). Tissue nutrient concentrations were validated against plant tissue standards analysed using the same procedures. Turfgrass plots were found to be slightly deficient of Fe and Mn (data not presented), and received two foliar applications of iron and manganese sulphates (25 kg Fe ha - 1, and 25 kg Mn ha -1 per application) each spring. 8

11 4.2.4 Turfgrass growth The dry mass of clippings collected when mowing the plots was used to measure turfgrass growth. Plots were mostly mown weekly, at a height of 15 mm, except in winter (July and August) when turfgrass growth slowed and plots were mown every two weeks. Clippings from each plot were collected, the fresh mass recorded before taking a subsample for determining the fresh : dry mass ratio, together from which the total clippings dry mass was determined. The water content of the subsample was calculated after oven-drying (60 C) for one week, and recording the dry mass. The clippings not included in the subsample were immediately redistributed across the surface of the respective plot. The lysimeter turfgrass was clipped at a height of 15 mm using shears, always on the same day as the turfgrass plots. Clippings were retained on the surface of the lysimeters Turfgrass quality Turfgrass quality was assessed by measuring turfgrass colour, surface hardness and tissue (clipping) N concentrations in the plots. Turfgrass colour was measured every four weeks from the start of the study, and following mowing, using a Chroma Meter (Minolta, CR-310, Osaka, Japan); an instrument previously shown to enable quantitative assessments of turfgrass colour (Landschoot and Mancino 2000). The meter describes colour in three coordinates: L*, lightness, from 0 (black) to 100 (white); a*, from -60 (green) to 60 (red); and b*, from -60 (blue) to 60 (yellow). As recommended by Landschoot and Mancino (2000), data used to assess turf greenness were the hue angles for the CIELAB colour space (Hamill and Camlin 1984). At any level of lightness, the hue angle is calculated as arctangent (b*/a*); the greater the hue angle the darker the greenness. Measurements were taken at three positions along a transect in each plot by pressing a 50 mm diameter measuring cylinder firmly down onto the canopy surface to exclude external light. The Chroma Meter was calibrated after every 36 readings, using a calibration plate (CR-A44, Minolta, Osaka, Japan) and following the instructions provided by the manufacturer. Surface hardness was measured every three months, and following mowing, using a 2.25 kg Clegg impact hammer (Dr Baden Clegg Pty Ltd, Perth, Australia). Measurements were taken in one position per plot by allowing the hammer to drop from a height of 450 mm three times and recording the values (in units of gravities) following the third drop. Total N concentration in clippings was measured every three months and by fine grinding an oven-dried subsample using a ball grinder, and analysing the tissue powder using a CHN analyser (LECO CHN 1000, MI, USA) Thatch and organic matter accumulation The accumulation of thatch in each plot was measured every three months by collecting a core (70 mm in diameter, 100 mm in height) and recording the height of the thatch plus shoots above the soil. Cores were collected the day following mowing. In addition, the effect of N treatments on the development of organic mat layers was also evaluated. A core (70 mm in diameter, 50 mm in depth) was collected from the soil surface, rhizomes removed, and then the remaining sample dried (105 C), weighed, and ground before being analysed for OM. Organic matter content was determined as the difference between dry mass (105 C for 48 h) and ash mass (600 C for 24 h). These soils contained no free CaCO 3. In addition, soil ph was measured annually as it has been suggested that decreases in soil ph resulting from N fertiliser applications, may lead to the decreased decomposition rates and the accumulation of thatch (Waddington 1992). Details of the soil ph method are provided below. 9

12 4.2.7 Leachate volumes and water analyses Leachate from each lysimeter was collected weekly. Leachate volumes were recorded, and subsamples frozen prior to analyses. Leachate samples for two consecutive weeks were proportionally bulked to make up 50 ml. Leachate samples were analysed for total N, NO 3 -, NH 4 + (every two weeks), and ph (every four weeks), and EC (every four weeks). Irrigation water samples were collected approximately weekly during irrigation periods and analysed for total N every two weeks. Total N concentration was determined after digesting samples using a modified method of Ebina et al. (1983). Briefly, 5 ml of sample and 5 ml of digest mix (0.074 M K 2 S 2 O 8, M NaOH) were autoclaved at 121 ºC for 30 min. Digestion converts N species to NO 3 - and NH 4 +. Nitrate and NH 4 + (in digested and undigested samples) were measured colorimetrically using a modified hydrazine reduction method (Downes 1978). Undigested samples were filtered through a polyethersulfone membrane (45 μm pore size) prior to measurement. Leachate ph was measured using a glass electrode, while EC was measured using a conductivity electrode Soil analyses Soil ph of the lysimeter soil (surface and subsoil) was measured initially, while the surface soil (0 50 mm) ph of the plots was measured annually. The soil ph of air-dried samples (sieved to <2 mm) was measured in a 1:5 soil : 0.01 M CaCl 2 suspension which had been shaken for 16 h. Samples were centrifuged (10 min at a relative centrifugal force of 850 G) before measuring ph with a glass electrode. Electrical conductivity (EC) of the lysimeter soil (<2 mm) was measured in a 1:5 soil : water suspension which had been shaken for 16 h. Soil cation exchange capacity of the lysimeter soil (<2 mm) was measured by shaking a 1:50 soil : 0.01 M silver thiourea suspension for 16 h and measuring the change in silver concentration using AAS (Rayment and Higginson 1992). Total C and N were measured by dry combustion of air-dry, finely-ground soils using a CHN analyser Industry benchmarking Critical values for Kikuyu turfgrass colour, N concentration and surface hardness are not well established for maintained turfgrass grown in south-western Australia. Consequently, every three months (one week following experimental measurements), we measured these parameters at six Kikuyu sports fields managed by local government so as to benchmark findings from our experimental site with industry sites. Turfgrass colour, N concentration and surface hardness were measured using the instruments and techniques described above Data analyses The amounts of N leached (and forms of N) were calculated every 14 d by multiplying leachate volumes (total after 14 d) by the concentrations of the N species in the leachates. These values were then summed to give a total N loss after 24 months. Organic-N leached was calculated by subtracting the amount of NH 4 + and NO 3 - leached, from the total N leached. All data were statistically analysed using Genstat (2007). A general analysis of variance was used to determine whether turfgrass age, N application rate and N application frequency affected measured parameters. Post-hoc pair-wise comparisons of means were made using LSD (significance level of 5%) calculated for each of the treatments and treatment interactions. The concentrations of NO 3 -, NH 4 + and organic-n in the leachate samples were highly skewed and could not be transformed to provide normally distributed data. 10

13 Consequently, only the median and range of concentrations for each of the N forms for each of the treatments are presented in the Results. However, when the amount of each N form leached after 24 months was calculated for each replicate, the data for total amounts of N, NO 3 - and organic-n leached were normally distributed and these data were analysed. 4.3 Results Environmental conditions and irrigation Total net evaporation, total rainfall, average air temperature and total irrigation for each month are presented in Fig The relative contributions of irrigation and rainfall differed depending upon the time of the year. Monthly irrigation ranged from mm, and exceeded rainfall from November to March each year; while monthly rainfall ranged from mm with the greatest falls recorded between May and September each year. Annual rainfall varied between the two study years, with 996 mm in 2005/06 and 628 mm in 2006/07. Monthly evaporation ranged from mm, with the greatest losses recorded between December and February each year (Fig. 4.1). Average monthly temperatures ranged from C, with the greatest average temperature reported in February or March (Fig. 4.1). The N concentrations in the irrigation water were low (< mg N L -1 ). Based on a median concentration (0.4 mg N L -1 ), the turfgrass plots received 13 kg N ha -1 in addition to fertiliser applications, during the 24 months Depth (mm) Temperature ( C) Air temperature Evaporation -20 Dec-04 Apr-05 Aug-05 Dec-05 Apr-06 Aug-06 Dec-06 Fig Average monthly distribution of irrigation, rainfall, leaching from turfgrass in lysimeters, evaporation and daily average air temperature. Values for leachate depths are means of 60 replicates. The mean standard error for the leachate depth represented 15% of the leachate depth mean, except in December 2005 (22%), March 2006 (20%), and November 2006 (17%) Bar symbols: leachate, irrigation, rainfall. 11

14 4.3.2 Turfgrass growth After 24 months, cumulative growth (clippings dry mass) ranged from 2372 kg ha -1 (younger turfgrass, nil fertiliser) to 12, 361 kg ha -1 (older turfgrass, 150 kg N ha -1 yr -1, 2 applications yr - 1 ) (Fig. 4.2). The cumulative dry mass of the clippings after 24 months was dependent upon turfgrass age (P<0.001), N application rate (P<0.001), and fertiliser application frequency (P<0.001) (Fig. 4.2). Consequently, on average, the older turfgrass produced at least twice the total clippings dry mass of the younger turfgrass at the same N application rates (Fig. 4.3), and possibly as a result of the older turfgrass deriving additional N from the mineralisation of soil N in the turfgrass sod (Qian et al. 2003). Increasing the N application rate to each turfgrass age increased growth. While increasing the application frequency from 2 times per year to every 4 weeks decreased growth on average by 20%, with the older turfgrass at the higher N application rate most affected (Fig. 4.2). Weekly growth (clippings dry mass) was not consistent throughout the year, and ranged from 2.6 kg DM ha -1 (younger turfgrass in winter, nil fertiliser) to 829 kg DM ha -1 (older turfgrass in autumn, 150 kg N ha -1, 2 applications yr -1 ) (Fig. 4.4). Growth tended to be greatest for each turfgrass age from late summer through to autumn, and least during the winter months, each year. Increasing the N application rate in combination with decreasing the application frequency further exacerbated the seasonal growth differences (Fig. 4.4) Turfgrass colour Turfgrass colour (hue angle) varied seasonally (P<0.001), with greatest overall greenness observed in spring and autumn (Fig. 4.5). During the study, colour depended upon turfgrass age (P<0.001) and fertiliser rate (P<0.05); with a stronger interaction between turfgrass age and fertiliser frequency (P<0.05). The older turfgrass plots tended to be greener than the younger turfgrass at all times and when averaged across N fertiliser treatments. Furthermore, increasing the N fertiliser rate increased turfgrass greenness for both turfgrass ages throughout the study (Fig. 4.5). For the first 11 months of the study, colour was also affected by N fertiliser application frequency; as splitting the annual N application across 2 applications tended to cause greater extremes in colour than the other application frequencies (Fig. 4.5). However, this effect of application frequency had different implications depending on turfgrass age. For the younger turfgrass the colour was not adversely affected by application frequency, whereas the colour of the older turfgrass plots fertilised 2 times per year often declined following the application in autumn, as the additional growth (Fig. 4.4) caused large sections of green shoots to be removed by mowing and the underlying (brown) thatch revealed (i.e., scalped ). Turfgrass colour (hue angle) at the sports fields ranged from 95 to 100, and like the experimental plots, varied seasonally (data not shown). If a hue angle of 100 is nominated as an industry standard, then all the older turfgrass treatments and only the younger turfgrass fertilised monthly (100 and 150 kg N ha -1 yr -1 ) or 4 times per year (150 kg N ha -1 yr -1 ) met the industry requirements throughout the study. 12

15 14000 a. Younger turfgrass Dry matter production (kg ha -1 week -1 ) b. Older turfgrass kg, 2 times /yr 50 kg, 4 times/yr 50 kg, 4-weekly 100 kg, 2 times/yr 100 kg, 4 times/yr 100 kg, 4-weekly 150 kg, 2 times/yr 150 kg, 4 times/yr 150 kg, 4-weekly Fig Influence of N management regime on dry matter produced (g dry clippings ha -1 week -1 ) from younger (a) and older (b) Kikuyu turfgrass plots after 24 months. Values are means (and standard errors) of three replicates. Dry matter production (kg ha -1 ) Younger turfgrass Older turfgrass N application rate (kg N ha -1 yr -1 ) Fig Influence of N supply on dry matter production (clippings) from younger and older turfgrass plots after 24 months. Values are means of nine values for N application rates (with replicates for application frequency pooled), and means of three values for nil N fertiliser treatments. 13

16 Younger turfgrass Older turfgrass 500 a. 50 kg N ha -1 yr b. 50 kg N ha -1 yr Dry matter production (kg ha -1 ) c. 100 kg N ha -1 yr -1 e. 150 kg N ha -1 yr d. 100 kg N ha -1 yr -1 f. 150 kg N ha -1 yr Jan-05 May-05 Sep-05 Jan-06 May-06 Sep-06 Jan-07 Jan-05 May-05 Sep-05 Jan-06 May-06 Sep-06 Jan-07 Date Fig Dry matter production (clippings) with time for the younger and older turfgrass receiving 50 kg N ha -1 yr -1 (a,b), 100 kg N ha -1 yr -1 (c,d) and 150 kg N ha -1 yr -1 (e,f) at different application frequencies. Values represent means ( standard errors) of three replicates. Frequency of application line graph symbols: nil N fertiliser, 4-weekly, 4 applications yr -1, 2 applications yr -1. Timing of fertiliser application symbols: 4-weekly, 4 applications yr - 1, 2 applications yr -1. Note the different scales for the younger and older turfgrass. 14

17 Influence of N rate on turfgrass colour 130 a. Younger turfgrass 125 b. Older turfgrass Hue Angle ( ) Hue Angle ( ) 85 Jan-05 May-05 Sep-05 Jan-06 May-06 Sep-06 Jan-07 Jan-05 May-05 Sep-05 Jan-06 May-06 Sep-06 Jan-07 Influence of N application frequency on turfgrass colour c. Younger turfgrass d. Older turfgrass Hue Angle ( ) Jan-05 May-05 Sep-05 Jan-06 May-06 Sep-06 Jan-07 Jan-05 May-05 Sep-05 Jan-06 May-06 Sep-06 Jan-07 Date Fig Influence of N rate (a, b) and N application frequency (c, d) on the colour of the younger and older Kikuyu turfgrass with time. Increasing hue angle indicates increasing greenness. Measurements were taken with a Chroma Meter. Values have been averaged across application frequency and represent means ( standard errors) of nine replicates for the N treatments, and means ( standard errors) of three replicates for the nil N treatments. Symbols: nil N fertiliser, 50 kg N ha -1 yr -1, 100 kg N ha -1 yr -1, 150 kg N ha -1 yr

18 4.3.4 Nutrient concentrations in leaf tissue dry matter The average tissue N concentration (% by dry mass) in clippings ranged from 1.07 to 3.56% (Fig. 4.6). Turfgrass age, N fertiliser rate and sampling time were the main factors affecting the N concentration of the clippings during the year (P<0.001). The N concentration in clippings from the older turfgrass was always greater than that of clippings from the younger turfgrass clippings. Furthermore, increasing the N fertiliser rate increased clipping N concentration. Turfgrass managers consider that leaf N concentration should be 2.0% to maintain Kikuyu turfgrass in the study region (Johnston 1996). Given this critical value, then all the older turfgrass treatments and the younger turfgrass fertilised at 150 kg N ha -1 yr -1 generally met the industry requirements throughout the study (Fig. 4.6) Surface hardness Surface hardness ranged from 37 to 110 gravities, and varied with time and turfgrass age (P<0.001); with a strong interaction between turfgrass age and N fertiliser rate over time (P<0.05) (data not shown). The surface of the younger turfgrass was harder than the older turfgrass throughout the study (P<0.05), however with time both surfaces tended to soften (P<0.05). Increasing the N application rate to the younger turfgrass decreased surface hardness. By contrast, applying N fertiliser had no effect on the surface hardness of the older turfgrass. Ideally, turfgrass surfaces for sports fields should exhibit a hardness of between 70 and 89 gravities, however any value between 31 and 120 can be considered acceptable (Chivers and Aldous 2003). After two years, only the younger turfgrass fertilised at 100 and 150 kg N ha -1 yr -1 had a surface hardness within the ideal range, although all the remaining treatments were within the acceptable range Thatch and organic matter accumulation Thatch + turfgrass leaf height (after mowing) varied from 8 to 36 mm during the study, and depended on turfgrass age, N fertiliser rate, and time after planting; data collected at the end of the study are shown in Fig The older turfgrass contained more thatch + leaf height than the younger turfgrass stands (P < 0.001), although by the end of the study the younger turfgrass receiving 150 kg N ha -1 yr -1 had similar amount as the older turfgrass receiving kg N ha -1 yr -1. Applying N fertiliser increased the thatch + leaf height of both turfgrass ages, and increasingly as N fertiliser rate increased (P < 0.001) (Fig. 4.7). For example after two years, increasing the N application rate from 50 to 150 kg N ha -1 yr -1 almost doubled the height of thatch + leaf for the younger turfgrass (Fig. 4.7). The OM content of the surface 50 mm of soil was only affected by turfgrass age, and did not change between one and two years following establishment. Averaged across fertiliser regimes and the two annual measurements, the surface soil C concentration (% by air-dried mass) was 24% for the older turfgrass, and 2.2% for the younger turfgrass Soil ph Surface soil (0 50 mm) ph ranged from 3.6 to 6.5 after one year, and 3.3 to 6.0 after two years. Soil ph was greater in the younger turfgrass (Year 1, ph 5.9; Year 2, ph 5.2) than the older turfgrass in both years (Year 1, ph 3.9; Year 2, ph 3.8) (P<0.001). Furthermore, increasing the N fertiliser rate decreased the soil ph for the younger turfgrass plots in both years (P<0.05), and the older turfgrass plots in the first year (P<0.05) (data not shown). For example, after two years the younger turfgrass plots receiving no fertiliser had a soil ph of 6.1, whereas the younger turfgrass plots receiving 150 kg N ha -1 yr -1 had a soil ph of

19 3.6 a. Younger turfgrass N concentration of clippings (%) b. Older turfgrass Jan-05 May-05 Sep-05 Jan-06 May-06 Sep-06 Jan-07 Fig Influence of N rate on the N concentration (% of dry mass) of the younger (a) and older (b) Kikuyu turfgrass with time. Values have been averaged across application frequency and represent means ( standard errors) of nine replicates for the N treatments, and means ( standard errors) of three replicates for the no N treatments. Symbols: no N fertiliser, 50 kg N ha -1 yr -1, 100 kg N ha -1 yr -1, 150 kg N ha -1 yr Younger turfgrass Older turfgrass Thatch + turfgrass leaf (mm) N application rate ( kg N ha -1 yr -1 ) Fig Influence of N rate on thatch + turfgrass leaf height (mm) of the younger and older turfgrass plots at the completion of the study. Values have been averaged across application frequency and represent means ( standard errors) of nine replicates for the N treatments, and means ( standard errors) of three replicates for the nil N treatments. 17

20 4.3.8 Leachate N concentration, ph and EC Nitrate concentrations in the leachate samples ranged from 0 to 78 mg N L -1 with the highest concentration reported for the younger turfgrass when N fertiliser was applied at the highest rate (150 kg N ha -1 yr -1 ). The median value for NO 3 - never exceeded 0.2 mg L -1 for any of the treatments. Ammonium concentrations ranged from 0 to 18 mg N L -1, with the highest concentration recorded for the older turfgrass at 100 kg N ha -1 yr -1 (Table 4.1). The median NH 4 + concentrations were all less than 0.2 mg N L -1. Organic-N concentrations ranged from 0 to 19 mg N L -1, with the greatest value recorded for the younger turfgrass with N fertiliser applied at the highest rate (150 kg N ha -1 yr -1 ) (Table 4.1). The median organic-n concentration appeared to vary between the turfgrass ages, with a median value of 1.2 mg N L -1 reported for the younger turfgrass and a median value of 2.6 mg N L -1 reported for the older turfgrass. Although leachate ph values ranged from 3.7 to 8.2, median values for treatments were close to neutral (data not shown). The EC of the leachate samples ranged from 72 to 3720 μs cm -1, with median values of 426 μs cm -1 for the older turfgrass and a median of 447 μs cm -1 for the younger turfgrass. Table 4.1. Leachate depth and N forms leached (median and range) during 24 months of Kikuyu turfgrass growth on a sandy soil, and as affected by turfgrass age and N fertiliser application rate. Median of N forms is of at least 127 values. N rate (kg N ha -1 ) Leachate depth (mm) Younger turfgrass (67) (27) (28) (40) Older turfgrass (33) (48) (55) (80) NO 3 - NH 4 + Organic-N (mg N L -1 ) (mg N L -1 ) (mg N L -1 ) Median Range Median Range Median Range The least significant difference for comparing leachate depth means, with maximum replicates, at the 5% level is 149. Values in brackets for leachate depths are standard errors. Values determined for leachate collected weekly, and measured 2-weekly, over 24 months. 18