Abstract
Three hydromulch planting techniques (hydroseeding, hydromulch capping of seedlings, and hydroplanting of seedlings) for Fimbristylis cymosa R. Br. (mau‘u ‘aki‘aki; Cyperaceae) were evaluated on compost-filled plots for the first 6 mo of planting. Hydro seeding comprised spraying a seed–mulch slurry at a rate of 437 live seeds/m2 (41 seeds/ft2) and 2200 kg/ha (1963 lb/ac) paper/straw mulch. Hydromulch capped seedlings comprised applying seedlings by hand to the surface at a rate of 199 plants/m2 (18 plants/ft2) and covering them with mulch at a rate of 4400 kg/ha (3926 lb/ac). Hydroplanted seedlings comprised spraying a seedling–mulch slurry at 199 plants/m2 (18 plants/ft2) with a mulch rate of 4400 kg/ha (3926 lb/ac). Hydroseeded plots attained the highest plant counts and exhibited the same monthly percent visual cover as hydromulch capped seedlings. Hydromulch capping of seedlings is a less-efficient planting method, as it required more time and resources for seedling preparation compared to hydroseeding. Results of the study support the recommendation of hydroseeding for large-scale planting and establishment of F. cymosa.
Field planting of Fimbristylis cymosa R. Br. (Cyperaceae) for seed production.
The use of native species in roadside revegetation has greatly increased over the past 20 y because of growing environmental awareness, recent plant material availability, and active promotion by the Federal Highway Administration (Knapp and Rice 1994; Harper-Lore 1996; Steinfeld and others 2007). In Hawaii, roadside revegetation with native plants is relatively new and is progressively gaining interest. Studies are currently underway on seed production, roadside establishment, and roadside maintenance techniques for a number of Hawaiian ground cover and shrub species. Over the next 20 y, the demand for native Hawaiian plants in roadside revegetation and urban landscaping is expected to increase because of the enactment of HB206/SB435, a state bill that requires increased use of indigenous and Polynesian-introduced plants in new and renovated publicly funded landscaping projects (OHA 2015).
Successful roadside revegetation with native plants requires efficient large-scale propagation and establishment techniques. Hydromulch planting is a well-established method for large-scale revegetation of roadsides. It was first developed in 1938 by the Connecticut State Highway Department as a means to plant difficult sites, such as steep slopes and other roadside areas (Button 1966; Pill and Nesnow 1999). Today, hydromulch planting goes beyond revegetation of steep slopes. It has been widely accepted and used for establishing turf in residential and other high-value landscapes (Pill and Nesnow 1999) and has also found applications in green roofs (Spall 1998).
Hydromulch planting makes use of a water carrier to apply seeds or vegetative plant propagules through a pump, delivering them by using a nozzle (Beard 1973). The system is generally composed of a large tank (378–6057 l [100–1600 gal]) connected to a pump, which provides hydraulic agitation and applies the seed–water mixture through a hose with a nozzle attachment (Steinfeld and others 2007). Aside from applying the basic seed and water mixture (hydroseeding), hydromulch planting mixes also contain mulch made of wood fiber (Emanual 1976), recycled paper or straw, fertilizer, biostimulants (Landis and others 2005; Steinfeld and others 2007), and herbicides (Lukas and others 2015). If the hydroplanting operation involves the application of vegetative plant parts, such as grass sprigs or rhizomes, the process is called hydrosprigging (Mellon 1989). Hydromulch planting operations in Hawaii are done mainly for erosion control purposes and for establishing turf in high-value areas such as golf courses, resorts, and residential lots. Commonly used species have primarily been nonnative, fast-growing grasses.
Fimbristylis cymosa R. Br. (Cyperaceae) (common names: mauʻu ʻakiʻaki, tropical fimbry, and hurricanegrass) is a low-growing coastal sedge that is native to the main Hawaiian Islands and across the Pacific Basin (Wagner and others 1999). Tolerance to salt, wind, and drought, coupled with an unusual leaf texture and dwarf growth form make it a highly desired ornamental species (Baldos and others 2012). Propagation of this species is easy using seeds or division of clumps. Because of these characteristics, F. cymosa is a recommended native ground cover for use in landscapes (Tamimi 1999) as well as for riparian restoration (Crago and others 2004). In addition to these applications, interest has increased in its potential use in roadside revegetation (Anonymous 2009).
To efficiently utilize F. cymosa for roadside revegetation applications, studies are necessary to assess its compatibility with hydromulch planting methods. In this study, we evaluate the efficacy of 3 hydromulch planting techniques (hydromulch capping of seedlings, hydroseeding, and hydroplanting of seedlings) in terms of plant counts per meter squared and percent coverage over a 6-mo establishment period.
Close-up of F. cymosa seedlings capped with hydromulch.
Close-up of F. cymosa seeds.
MATERIALS AND METHODS
Planting Material and Seed Source Establishment
Stock plants of F. cymosa (HA#5866, 9079806) were sourced from the USDA Natural Resource Conservation Service (NRCS) Hoʻolehua Plant Materials Center in Molokaʻi. In June 2006, a soilless nursery was constructed at the University of Hawaii Magoon Research and Instructional Facility to increase plant material for the propagation study. Barerooted clumps of the sedge were planted in commercially available growing media composed of a mix of compost and volcanic cinder (Menehune Magic Black Cinder Blends, Hawaiian Earth Products, Kapolei, Hawaii). Stock plants were allowed to establish and to set seeds for 6 mo.
Seed Counts and Seed Germination Tests
Prior to field evaluation of hydromulch planting techniques, we conducted seed counts and a seed germination test to estimate the number of seeds per unit weight and the average percent germination of seeds. Inflorescences of F. cymosa were harvested and air-dried. Seeds were recovered from crushed seed heads through a combination of sieving and air-blowing until most of the plant residue was removed. Seeds were stored dry (50% relative humidity) at approximately 10 °C (50 °F) until use.
To estimate the number of seeds contained per unit weight, we manually counted 5 samples of seeds, 0.02 g in size. The mean seed count per sample was used for estimating the amount of seeds needed for the hydromulch planting experiment. In addition to seed counts, we conducted a seed germination test to determine the percent germinable seed for a given sample. One hundred seeds were sown in each of 4 Petri plates (100 mm diameter, unsealed) lined with moistened filter paper (Whatman #3, Whatman International, Maidstone, UK). The sown seeds were allowed to germinate inside an incubator (Percival Scientific, Perry, Iowa) with alternating dark and light periods (12 h each, under fluorescent lights) as well as fluctuating day (26 °C/78.8 °F) and night (20 °C/68 °F) temperatures. We evaluated seed germination on a weekly basis. Seeds that had ≥2 mm (0.08 in) radicle or shoot protrusion were counted as germinated. Cumulative percent germination was recorded after 1 mo.
Field Assessment of Hydromulch Planting Techniques
We evaluated 3 hydromulch planting techniques in terms of plant count and percent visual cover from September 2007 to March 2008: 1) hydromulch capped 2-mo-old seedlings (applied by hand to the surface of each experimental unit); 2) hydroplanted 2-mo-old seedlings; and 3) hydroseeding (Figure 1). Fimbristylis cymosa seeds and plantlets were prepared 2 mo prior to the application of the hydroplanting treatments. For treatments involving plantlets, seeds were sown in galvanized iron trays filled with a mixture containing 40% (by volume) black volcanic cinder and 60% (by volume) commercial potting mix (Promix, Premier Horticulture, Quakertown, Pennsylvania). Seeding rate was approximately 0.85 g/m2 or an average of 0.15 g of seed per tray (∼2250 seeds). Seeds were allowed to germinate and grow for 2 mo under overhead sprinkler irrigation and full sun conditions. Seedlings were approximately 2.5 cm (1 in) in diameter and had 6 to 7 leaves.
The 3 hydromulch planting techniques evaluated in this study: hydromulch capped seedlings (A); hydroseeding (B); and hydroplanted seedlings (C).
To prepare the planting surface for the hydromulch treatments, 4 raised plots (9.3 m2 [100 ft2] in size; 5.08 cm [2 in] in depth) framed with polyvinylchloride (PVC) pipes were installed at the H1-University Avenue off-ramp cloverleaf. The PVC frames were placed on a black plastic woven geotextile fabric to reduce weed pressure. To keep the growing medium in place, the bottom of each plot was lined with a layer of plastic sheeting. Drainage was provided by perforating the plastic sheeting on the low regions of the plot. To ensure a weed-free environment, commercially available compost (Menehune Magic Black Cinder Blends, Hawaiian Earth Products, Kapolei, Hawaii) was used as the growing media for this experiment. After the addition of compost, the plots were limed (Dolomite 65 AG, Chemical Lime Company, Salinas, California) at 2.24 tons per ha (1813 lb/ac) (54.7% CaCO3, 42.6% MgCO3) and fertilized with triple superphosphate (0-46-0) at 224 kg P per ha (200 lb/ac). The growing medium was kept moist prior to planting to maintain soil capillary action.
A day prior to hydromulching, the seedling clumps were separated into individual plantlets through gentle agitation underwater. Seedlings were cleaned and kept moist until ready for use. We used approximately 70 g of plantlets (equivalent to 616 plants) in each of the hydromulch-capped seedling treatments (applied by hand to the surface of each experimental unit) and the hydroplanted seedling treatments. This quantity is equivalent to a sowing rate/planting density of 199 plants/m2 (18 plants/ft2). For the hydroseeded treatment, 0.1 g of seeds (containing approximately 1490 seeds) was used to provide a seeding density equivalent to 481 seeds/m2 (45 plants/ft2) (Figure 2).
Photo displays the amount of Fimbristylis cymosa seed used in the hydroseeding treatment. The vial contains 0.1 g or approximately 1500 seeds.
Except for seedlings capped with hydromulch, all materials in each of the 2 other treatments were mixed together and applied using a hydroseeder. Table 1 lists the amount of tackifier (C:tac, Hamilton Manufacturing, Twin Falls, Idaho), paper mulch (NaturesOwn, Hamilton Manufacturing, Twin Falls, Idaho), and water used for each treatment. A hydromulch delivery system (Turbo Turf Modular Hydroseeding System Model No. HS-50-M, Turbo Technologies, Beaver Falls, Pennsylvania) used for applying the treatments consisted of a 190-l (50.2-gal) tank and a 5 × 5 cm (2 × 2 in) centrifugal trash pump calibrated to apply approximately 114 l (30 gal) of hydromulch per min.
Amount of planting material, tackifier, paper mulch, and water used for each of the hydroplanting treatments. Hydromulch planting materials were applied using the Turbo Turf Modular Hydroseeding System (Model No. HS-50-M). Each batch of hydromulch covered 3.1 m2 of experimental area per block.
During the application of hydromulch, untreated plots were masked with plastic fabric to prevent cross-plot contamination. The hydroseeding machine was completely flushed with water before the next treatment was prepared. Each treatment was replicated 4 times and arranged in a completely randomized block design. Each treatment covered 3.1 m2 (33.4 ft2) of experimental area per block. For the first 4 mo of the experiment, overhead irrigation was applied 3 times per day (early morning, noon, and late afternoon) for 5 min to prevent the hydromulch from drying. After 4 mo, irrigation was reduced and applied once a day (early mornings) for 10 min.
Plant counts and visual percent cover were recorded from 3 randomly selected 30.5 cm × 30.5 cm (1 ft2) representative portions of each experimental unit. Plant counts were collected for the first 2 mo after planting while visual percent cover was recorded during the first 6 mo after planting. Supplemental hand-weeding was employed during the 6-mo observation period to remove competition and to improve the accuracy of visual cover ratings. Monthly percent visual cover was measured by superimposing 100 square grids on digital photographs of a representative area (Figure 3). Representative areas were photographed at a constant height to provide a cropped sample with square dimensions of 1570 × 1570 pixels. This procedure was facilitated by framing the edges of a PVC square (30.5 cm × 30.5 cm [1 ft × 1 ft]) on the camera viewfinder. Collection of percent visual cover was facilitated by viewing the grid-imposed photos in digital imaging software (Adobe Photoshop CS2, Adobe Systems, San Jose, California). Estimations per sample area were assessed by counting the number of squares fully covered with leaves and vegetation. Average percent cover of the 3 sample areas was calculated to obtain the percent cover of a treatment plot.
Estimating percent visual cover of F. cymosa in Adobe Photoshop. Digital photographs of the sample were superimposed with 100 square grids. Percent visual cover was estimated by counting the number of squares occupied by foliage.
Plots containing the 3 different hydromulch planting treatments. Photo by Joseph DeFrank
Spreading the seedlings on the plot prior to capping with hydromulch. Photo by Joseph DeFrank
Treatment plots 5 mo after planting.
Treatment plots 6 mo after planting. Photo by Joseph DeFrank
Treatment plots with the 190-l (50-gal) hydromulcher.
Repeated measures analysis was carried out using Statistix 9.0 (Analytical Software, Tallahassee, Florida). For plant count data, all 3 treatments (that is, planting methods) were included in the analysis. Tukey’s all pairwise comparisons test was used to separate treatment means. For percent cover data, the repeated measures analysis used data only from the hydromulch capped seedlings and the hydroseeded plots. The hydroplanted treatment was excluded in the analysis due to consistently low percent cover values (0–7%) even at 6 mo after planting. Tukey’s all pairwise comparisons test was used to separate differences in percent cover between months.
RESULTS
Seed Counts and Seed Germination Test
Average number of seeds per 0.02 g, based on 5 samples, was 298 or approximately 15,000 seeds per g. Average percent germination for F. cymosa after 1 mo of incubation was 91 ±2.5%. Seeding density of the hydroseeding treatment therefore contained approximately 437 live/viable seeds per m2.
Plant Counts
No significant interaction occurred between treatment and month of observation, therefore treatment means were pooled across months (first 2 mo). Significant differences between planting methods were observed during the first 2 mo after planting. Hydroseeded plots exhibited the highest seedling density based on plant counts (Figure 4). Hydroseeded treatments had an average density of 267 plants/m2 with 61% survival of the viable seeds applied to these treatments. Hydromulch capped plots exhibited significantly lower plant density (76 plants/m2) compared to the hydroseeded treatments. Percent survival of hand-sown seedlings based on initial plant density (199 plants/m2) was 38%. Hydroplanted plots exhibited the lowest mean plant counts (2 plants/m2) and percent survival (1%).
Plant counts per m2 of the F. cymosa planting treatments pooled over the 2 mo after planting. Hydroseeded treatments exhibited the highest number of plants per m2 among the 3 treatments. Values with the same letter are not significantly different at P < 0.05, n = 8.
Percent Visual Cover
Data analysis did not reveal a significant interaction between the factors of months after planting and method of planting treatments. Means were therefore pooled across planting method treatments within each month. Percent visual cover significantly increased within the first 6 mo of observation (Figure 5). During the first 2 mo after planting, plots (hydroseeded and hydromulch capped seedling treatments) exhibited < 10% cover. At 6 mo after planting, percent cover of plots (hydroseeded and hydromulch capped seedling treatments) increased to 61%. Figure 6 shows the progression of the hydroplanting treatments over the 6-mo observation period.
Percent visual cover of F. cymosa established for a period of 6 mo. No significant interaction between months after planting and planting treatments were observed. No significant differences between planting treatments were observed. Significant differences between months were observed, therefore, percent visual cover was pooled between hydroseeded and hydromulch capped seedling treatments. Pooled means are shown as numerical values above the bar graphs. Hydroplanted treatment was excluded in the statistical analysis due to zero to low percent cover (< 7%). Values followed by the same letters are not significantly different as determined by Tukey’s range test at P < 0.05, n = 8.
Fimbristylis cymosa hydromulch planting treatments over a period of 6 mo: hydromulch capped seedlings (A); hydroseeding (B); hydroplanted seedlings (C). Photos were taken at 1, 2, 4, and 6 mo after planting.
DISCUSSION
Results indicate that hydroseeding was the most effective and efficient means of establishing large-scale F. cymosa plantings. Hydroseeding requires less time and resources to establish the same percent visual cover as hydromulch capping of seedlings. The hydroseeding operation requires only one step, which includes mixing all the materials in one tank and applying it directly to the prepared planting surface. By contrast, the hydromulch capping method requires a 3-step process that includes producing the seedlings (2-mo growing period), then distributing them evenly over the planting area followed by application of the hydromulch cap. Aside from taking less time and resources, hydroseeding also exhibits higher percent cover at all dates after planting as compared to the other treatments. We conclude that hand-sown seedlings provide less coverage because of seedling mortality and slow growth due to outplanting shock.
Failure of the hydroplanted seedlings to produce vegetative cover was attributed to mechanical damage caused by passage through the pump (Figure 7). At the end of the hydroplanting process, pieces of seedlings were often observed in the hydroplanted plots. Although mixing the seedlings in the hydromulch slurry is not recommended, the use of primed or barely germinated seeds may provide better results. A study by Tilley and St John (2013) indicated that either stratified or germinated Nebraska sedge (Carex nebrascensis Dewey [Cyperaceae]) seeds can be planted through hydroseeding. Results, one mo after planting, showed that hydroseeded plots had significantly more plants than hydromulch capped plots.
Mechanical damage incurred by hydroplanted F. cymosa seedlings during the planting process.
In summary, this study indicates that hydroseeding can be used for large-scale planting and establishment of F. cymosa. Hydroseeding takes less time and resources for establishment in contrast to hydromulch capping of seedlings or hydroplanting. The small seed size of F. cymosa eased planting operations by reducing the bulk of planting materials and by streamlining the process into a one-step operation. The hydroseeding survival rate is also higher than hydromulch capping of seedlings and hydroplanting of seedlings.
ACKNOWLEDGMENTS
We thank the Hawaii Department of Transportation for providing funding for this study and the USDA NRCS Hoʻolehua Plant Materials Center for providing technical assistance and also for providing stock plants for this study. We thank the Magoon Facility Staff for helping us install the experiments at the H1-University off-ramp research demonstration site.
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