Turfgrass Response Research Articles

Effect of biological additives to a putting green with low plant‐available phosphorus

AbstractThe use of phosphorus fertilizers on managed turf has become discouraged, if not restricted, in many places because of the risk of pollution of surface waters posed by excessive phosphorus application. Therefore, nontraditional options to increase phosphorus availability to turf are worthy of investigation. The objectives of this study were to evaluate the effect of additions of arbuscular mycorrhizal fungi and an N‐fixing bacterium, Methylobacterium symbioticum, on the nutritional status of a mature bentgrass putting green on a sand root zone with low plant‐available phosphorus status. The biological amendments were added at various intervals after aerification, and turfgrass responses were recorded over two field seasons. Mycorrhizae did not result in increased turfgrass visual quality, clipping yield, or clipping P content. Additions of the N‐fixing bacterium resulted in increased mid‐season clipping N content and increased visual turfgrass quality, but the overall effect was relatively small. It appears that applications of M. symbioticum to turfgrass hold promise for improving nutrient use efficiency and visual turfgrass quality and deserve future exploration.

Two golf course putting green turfgrass responses to urea nitrogen and nickel

Two golf course putting green turfgrass responses to urea nitrogen and nickel

Urea Cocrystals as a Potential Fertilizer for Turfgrass: Responses of ‘Tifway’ Hybrid Bermudagrass and Nitrogen Release Behavior

Urea cocrystal materials are a potential fertilizer source that has shown to decrease environmental nitrogen losses. Novel nitrogen (N)-containing urea cocrystal fertilizers, CaSO4·4urea (UC1) and Ca(H2PO4)2·4urea (UC2), were synthesized using the mechanochemical method to form stable urea cocrystals to be tested as a fertilizer source for turfgrass. The objectives of this study were to 1) evaluate the response of ‘Tifway’ hybrid bermudagrass (Cynodon dactylon × C. traansvalensis Burt Davy) to N fertilization by urea cocrystals and traditional coated urea products (MU·PCU, methylene urea, urea, polymer-coated urea; PCU, polymer-coated urea, urea) supplied at two rates at the beginning of two, 10-week study periods conducted under a greenhouse setting and 2) investigate N release behavior of urea and two cocrystal products using a rapid water release test. In the turfgrass response study conducted in the greenhouse, improved turfgrass quality above the minimum quality threshold was observed when averaging across all products. For normalized difference vegetation index (NDVI), cocrystal outperformed all other products in the summer study and both cocrystal products outperformed the traditional product (MU·PCU) in the winter study. Further, both cocrystal products showed favorable growth responses compared with the commercial products provided by positive clipping production and vertical extension rates. In the nitrogen release experiment, a rapid water release test revealed the N release peak of urea was significantly higher than both UC1 and UC2. Furthermore, significantly higher N was leached from urea (15% loss) compared with both UC1 and UC2 (≈8% loss). Results from both studies provide evidence supporting suitability of urea cocrystal application on bermudagrass and potential as a slow-release fertilizer source through sustained turfgrass vigor, growth, decreased N release peak, and decreased leaching losses.

Evaluation of different bermudagrass germplasm at physiological and molecular level under shade along longitudinal and latitudinal gradients

Responses of turfgrass to shade vary in individual species, and the degree and quality of low light; therefore, the selection of low light tolerant cultivars of turfgrass is important and beneficial for turf management rather than other practices. The stolons of thirteen bermudagrass genotypes were planted with two treatments and three replications of each treatment to establish for one month in the Yangzhou University Jiangsu China greenhouse. The established plants were transferred outside of the greenhouse, and 50% shading was applied to them with a black net. After 30 days of stress treatment, the morpho-physiological and biochemical analyses were performed. The expression of genes such as HEMA, HY5, PIF4, and Cu/ZnSOD was assessed. Cynodon dactylon is a C4, and perennial that grows as lawn grass and is used as forage. Based on different indicator measurements, the most shade-tolerant germplasm was L01 and L06 along the longitudes and L09 and L10 along the latitudes. At the same time, L02 and L08 were more susceptible, respectively. However, germplasm showed greater tolerance in higher latitudes while longitudinal plants showed less stress response. The current study aimed (1) to screen out the most shade-tolerant Cynodon dactylon genotype among 13 along longitudinal and latitudinal gradients in China. (2) to examine morpho-physiological indicators of different bermudagrassgenotypes; (3) to evaluate if and how differences in various indicators of bermudagrass correlated with geographic region. This study will significantly advance the use of Cynodon germplasm in breeding, genomics, management, nomenclature, and phylogeographical study. It will decisively define whether natural selection and migration can drive evolutionary responses for populations to adapt to their new environments effectively.

Brown patch severity as affected by cool‐season turfgrass species, cultivar, and nitrogen rate

AbstractBrown patch (caused by various Rhizoctonia and Rhizoctonia‐like species) is a major summer disease for several cool‐season turfgrass species, including creeping bentgrass (CBG) (Agrostis stolonifera L.), colonial bentgrass (CLBG) (Agrostis capillaris L.), perennial ryegrass (PRG) (Lolium perenne L.), and turf‐type tall fescue (TTTF; [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.]). Elevated nitrogen (N) rates are suggested to enhance development of brown patch symptoms. A controlled environment study was conducted to determine the influence of two N rates among four cool‐season turfgrass species maintained at 1.9 cm after inoculation with R. solani. Field‐grown plants of four CBG cultivars, a CLBG cultivar, a PRG blend, and two TTTF cultivars were fertilized weekly, totaling 49 and 196 kg N ha−1 across four applications. Turfgrass responses were measured as relative growth rate, brown patch severity, and seasonal brown patch using area under the disease progress curve (AUDPC). On average, peak brown patch severity among the species and cultivars was between 22.6% and 68.1% for Raptor III TTTF and Penn A‐1 CBG, respectively. Turf‐type tall fescue cultivars decreased brown patch by 61% compared to CBG, CLBG, and PRG. The lower N rate reduced brown patch AUDPC by 17% and 33% for CBG and PRG, respectively, but N rate generally had no effect for CLBG and TTTF. These results reinforce the importance of planting disease‐resistant species and cultivars. Additionally, N rate may be an important factor affecting brown patch severity for select intensively managed turfgrass species.

Novel Curve Fitting Analysis of NDVI Data to Describe Turf Fertilizer Response

Evaluating the effectiveness of fertilizers on crops without traditional yield is difficult, as clipping collection is time-consuming and not indicative of the desired response to the fertilizer. Remote sensing techniques, like the normalized difference vegetation index (NDVI), have emerged as an effective tool to combat these issues. Canopy reflectance, measured by NDVI, is commonly used to differentiate turfgrass response to nitrogen (N) fertilization treatments; however, advancements in data processing are needed for greater differentiation between treatments and better testing of the effects of fertilizer responses. Presented here is an advancement in the processing of NDVI data by applying a compound exponential (pulse peak) function to changes in NDVI over time, relative to a control. This method’s effectiveness in differentiating between fertilizers was evaluated by applying polymer-coated urea (PCU), an enhanced efficiency fertilizer (EEF), and urea on turfgrass to show the usefulness of the novel curve fitting in highlighting differences in fertilizer response. The field study was carried out on an established Kentucky bluegrass (Poa pratensis L.) blend on a sandy loam soil rootzone maintained with a typical home lawn maintenance regime. Ratios of PCU to urea ranging from 100% urea to 100% PCU with increments of 20% of PCU were used to observe a continuum of response between the two fertilizer types. The N rate for all blends was 73 kg ha−1, with unfertilized plots used as a control to set baseline measurements for the curve fitting. Turfgrass response to N fertilization treatments was assessed through visual turfgrass quality ratings, dry matter yield, and canopy reflectance, where higher urea content resulted in the shortest time to maximum ∆NDVI (24 days), while 100% EEF reached maximum ∆NDVI at 56 days. The novel curve fitting analysis of the NDVI data allowed for differentiation between treatments, provided a measure of fertilizer effects, and differentiated between urea and enhanced efficiency fertilizers.

Morphophysiological Responses of Two Cool-Season Turfgrasses with Different Shade Tolerances

Understanding the differences in cool-season turfgrass responses to shade is critical for future turfgrass management and breeding for improved shade tolerance. The purpose of this study was to evaluate the shade-tolerance mechanisms of two cool-season turfgrass species in terms of turf performance, growth, and physiological characteristics. Two turfgrass species, namely, ’SupraNova’ (Poa. supina Schrad.) and ‘Lark’ (Lolium perenne L.), were subjected to 0 (CK, unshaded), 35% (LS), 70% (MS), and 92% (HS) shade, respectively. Compared with ‘Lark’, ‘SupraNova’ showed better turf quality (TQ) and turf color intensity (TCI) under shade. The total length and surface area of the roots of ‘Lark’ gradually decreased as the shade increased, while those of ‘SupraNova’ increased and then decreased with increasing shade. The chlorophyll fluorescence photochemical quenching coefficient (qP), electron transport rate (ETR), and maximum quantum yield of primary photosystem II (PSII) photochemistry (Fv/Fm) decreased significantly under HS; however, these decreases were more significant in ‘Lark’ than in ‘SupraNova’. The leaf reflectance of the two turfgrasses under shade was lower than that under CK, but the leaf reflectance of ‘Lark’ was higher than that of ‘SupraNova’ in the visible light band. The normalized difference vegetation index (NDVI) of the two grasses first decreased and then increased. The NDVI of ‘Lark’ under shade was slightly higher than that under CK. ‘SupraNova’ showed strong tolerance on the basis of malondialdehyde (MDA), hydrogen peroxide (H2O2), superoxide anion (O2·−), and ascorbic acid (AsA) contents and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity. The MDA, H2O2, O2·−, and AsA contents and SOD, POD, and CAT activity (which represent indicators) changed the most under MS. Taken together, the results indicated that the adaptability of ‘SupraNova’ to shade was better than that of ‘Lark’.

Effects of plant biostimulants on seedling root and shoot growth of three cool‐season turfgrass species in a controlled environment

AbstractA plant biostimulant is a natural substance or microorganism applied to plants or soil to enhance growth and stress tolerance. The objective of this study was to measure the effect of six commercial plant biostimulants on root and shoot production in seedlings of three cool‐season turf species grown in a controlled environment. Lolium perenne L., Agrostis palustris Huds., and Schedonorus arundinaceus Schreb. were seeded into tobacco float trays and, after germination, were installed in a hydroponic system receiving a half‐dose Hoagland solution. Fifteen days after seeding, seedlings were treated with six different plant biostimulants applied within each float tray and then grown in a greenhouse for 25 d, following a split‐plot design. Photosynthetically active radiation, air temperature, and humidity were monitored for the duration of the study. The experiment was conducted twice. Fresh weight, dry weight, and total nonstructural carbohydrates were measured. The study showed that humic substances and complex organic materials had a positive effect on turfgrass performance, and there are species differences in the responses of turfgrass.

Response of Hybrid Bermudagrass and Manilagrass to Soil Moisture Using Water-table Depth Gradient Tanks

Previous research involving turfgrass response to soil moisture used methodology that may compromise root morphology or fail to control outside environmental factors. Water-table depth gradient tanks were employed in the greenhouse to identify habitat specialization of hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy] and manilagrass [Zoysia matrella (L.) Merr.] maintained at 2.5 and 5.1 cm. Turfgrass quality (TQ), normalized difference vegetation index (NDVI), canopy temperature (CT), and root biomass (RB) were used as metrics for plants grown in monoculture in sandy clay loam soil. Mowing height did not affect growth of turfgrass species in response to soil moisture. Turfgrass quality, NDVI, and RB were greatest, whereas CT was lowest at wetter levels [27- to 58-cm depth to the water-table (DWT)] of each tank where plants were growing at or above field capacity. However, bermudagrass RB was greatest at 27-cm DWT, whereas manilagrass RB at 27-cm DWT was lower than RB at 42.5- to 73.5-cm DWT in 2013 and lower than all other levels in 2014. Both species responded similarly to droughty levels (120- to 151-cm DWT) of the tanks. Turfgrass quality, NDVI, and RB were lowest, whereas CT was highest at higher droughty levels. Bermudagrass may be more competitive than manilagrass when soil moisture is high whereas both species are less competitive when soil moisture is low.

Force-limiting and the mechanical response of natural turfgrass used in the National Football League: A step toward the elimination of differential lower limb injury risk on synthetic turf

Lower limb injury rate in the National Football League (NFL) is greater on synthetic turf than on natural turfgrass. Foot loading in potentially injurious situations can be mitigated by damage to natural turfgrass that limits the peak load by allowing relative motion between the foot and the ground. Synthetic turf surfaces do not typically sustain such damage and thus lack such a load-limiting mechanism. To guide innovation in synthetic turf design, this paper reports 1) the peak loads of natural turfgrass when loaded by a cleated footform and 2) corridors that define the load–displacement response. Kentucky bluegrass [Poa pratensis, L.] and two cultivars of hybrid bermudagrass [Cynodon dactylon (L.) Pers × C. transvaalensis Burtt Davy] were tested with two cleat patterns in three loading modes (anterior-posterior or AP translation, medial–lateral or ML translation, and forefoot external rotation) at two power levels (full-power, which generated potentially injurious loads, and reduced-power, which generated horizontal forces similar to non-injurious ground reaction forces applied by an elite athlete during play). All tests generated peak force<4.95 kN and torque<173 Nm, which is in a loading regime that would be expected to mitigate injury risk. In full-power tests, bermudagrass withstood significantly (p < 0.05) greater peak loads than Kentucky bluegrass: (3.86 ± 0.45 kN vs. 2.66 ± 0.23 kN in AP, 3.25 ± 0.45 kN vs. 2.49 ± 0.36 kN in ML, and 144.8 ± 12.0 Nm vs. 126.3 ± 6.1 Nm in rotation). Corridors are reported that describe the load–displacement response aggregated across all surfaces tested.

Determining Nitrogen Fertilizer Cost Using Turfgrass Response

Numerous nitrogen (N) sources are used in turfgrass management and vary from soluble to slow-release. Determining the least expensive N source can be confusing for consumers. Price per ton and price per pound N are common price comparison methods. An improved approach could use longevity of the N source to balance the price. The objective of this study was to determine the longevity of turfgrass response to N sources and to determine the cost to achieve such responses. This study was conducted in Ft. Lauderdale and Jay, FL, from 1 Jan. to 31 Dec. 2018 on ‘Riley’s Super Sport’ (Celebration®) bermudagrass (Cynodon dactylon). Treatments included nontreated turfgrass, urea, ammonium sulfate, stabilized urea, methylene urea, ureaformaldehyde, two natural organics, sulfur-coated urea, and two polymer-coated urea fertilizers. Treatments were arranged in a split-plot design with N sources as whole plots and N rate (N applied at 49 and 98 kg·ha−1 every 4 months) as subplots. Turf quality was recorded on a scale of 1 to 9, where 1 = dead/brown turf and quality, 6 = minimal acceptable, and 9 = optimal healthy/green turf. Turf quality ratings were recorded weekly and used to determine response longevity (days quality ≥6.0) and area under the turfgrass response curve (AUTRC). Urea resulted in response longevity greater than or equal to other N sources during each season except when applied at 98 kg·ha−1 of N during the fall fertilizer cycle in Jay. Natural organics were ≈6-fold more expensive than urea in Jay and Ft. Lauderdale using turfgrass response longevity and AUTRC. Urea and sulfur-coated urea were the least expensive soluble and slow-release N source, respectively, using dollars per pound N, dollars per acre per day, and dollars per acre per quality-day during each fertilizer cycle and annual average in Jay and Ft. Lauderdale. No evidence was found supporting the use of turfgrass response as a more effective method of determining fertilizer cost than dollars per pound N.

Turfgrass response to flazasulfuron and trifloxysulfuron sodium deposited by runoff water

AbstractFlazasulfuron is a selective herbicide registered for use in warm‐season turfgrass. Concerns have been raised over its mobility in surface water runoff. Studies were conducted in Blacksburg, VA and Charlottesville, VA to evaluate injury to Lolium perenne L. (perennial ryegrass) downslope of plots treated with transition‐assisting herbicides, including flazasulfuron, pronamide, and trifloxysulfuron sodium. Flazasulfuron (52 g a.i. ha–1) and pronamide (1120 g a.i. ha–1) consistently injured L. perenne greater than trifloxysulfuron sodium (17 g a.i. ha–1) or lower rates of flazasulfuron (9 and 26 g a.i. ha–1). At Charlottesville, soil was more saturated, and a natural rainfall increased the rate of runoff and severity of L. perenne injury below treated plots. At this site, flazasulfuron (52 g a.i. ha–1) and pronamide (1120 g a.i. ha–1) caused visible injury to L. perenne 10 to 16 m below treated plots. Based on L. perenne injury, flazasulfuron mobility at the rates tested can be considered equivalent or greater than trifloxysulfuron sodium, and equivalent or less than pronamide when subjected to excessive irrigation or rainfall soon after application to saturated soils. Precautions should be taken to avoid application of these herbicides to saturated soils and apply when rainfall is not expected for sufficient time to rinse turfgrass foliage and incorporate nonabsorbed herbicide into soil via light irrigation.

Review of cool‐season turfgrasses for salt‐affected roadsides in cold climates

AbstractTurfgrass is often planted along roadsides because of its adaptability and capacity to perform a wide range of functions. Like other roadside vegetation, it must withstand a wide range of biotic and abiotic stresses while persisting long term with minimal management inputs. In cold‐weather climates, snow and ice management practices on roads include the use of deicing salts. Deicing salts can have negative impacts on infrastructure and the environment including soil structure degradation, surface and ground water contamination, and reduction of vegetation quality along roadsides. Insights from past evaluations of turfgrass response to stresses experienced on roadsides can provide perspective for future approaches. This review provides historical context for the establishment of turfgrasses as roadside vegetation in cold‐weather climates where deicing salts are used. Adaptability of species for roadside applications as well as field and controlled environment evaluations of salt tolerance are discussed. In future studies, improved characterization of roadside stress and broader collaborative evaluation programs can enhance testing and result in improved specifications for roadside turfgrass species and mixtures.

Drought response of urban trees and turfgrass using airborne imaging spectroscopy

Vegetation growth and physiological functioning, including carbon uptake and transpiration, can be strongly affected by drought. During water-limited conditions, urban vegetation may be limited in its ability to provide ecosystem services, such as shading and evaporative cooling. While there has been extensive research on drought response in natural vegetation and agricultural systems using remote sensing, drought impacts on urban vegetation have remained understudied. With >50% of people worldwide living in cities and the increased potential for future droughts, it is important to understand how urban vegetation will respond and to evaluate potential impacts. Here, we used repeat flights of NASA airborne imaging spectroscopy (AVIRIS and AVIRIS-NG) to quantify the responses of common urban tree species and turfgrass in downtown Santa Barbara, California, USA to the 2012–2016 California drought. The effects of the drought on vegetation were quantified using several spectral indicators: fractional cover from multiple endmember spectral mixture analysis (MESMA), vegetation indices, and continuum removed absorption features. We used existing tree crown object polygons that were classified to species and had associated estimates of pre-drought leaf area index and biomass. We also included polygons of turfgrass parks and recreational fields. All tree species and turfgrass had four or more spectral indicators with significantly lower mean values (p < 0.05) during the drought in 2014, and evidence of recovery was observed for some species in 2017, which was after the drought had ended. In general, needleleaf and native trees were more affected than broadleaf and non-native trees, respectively, but with considerable interspecific variability. Based on the spectral indicators, turfgrass cover senesced in the middle of the drought but recovered soon after the drought ended, whereas the majority of tree species had not fully recovered. Mean green vegetation cover declined in most tree canopies during the drought, primarily exposing paved surfaces and/or non-photosynthetic vegetation, depending on the site type and tree patch size. Drought impacts as expressed in spectral indicators were generally more severe in tree patches with high pre-drought leaf area index, suggesting that denser, leafier canopies were more difficult for trees to maintain during the drought. Most spectral indicators were correlated with one another (R > 0.4), suggesting co-occuring adjustments of greenness, water content, and plant pigments.

Kentucky bluegrass growth under saline, waterlogging, and saline‐waterlogging conditions during germination and seedling growth

AbstractSalinity and waterlogging, two major problems in turfgrass management, often co‐occur in nature; however, information on the response of turfgrass to the combined salinity‐waterlogging stress is limited. The objective of this study was to determine growth response of nine Kentucky bluegrass (Poa pratensis L.) cultivars to the control (i.e., non‐stress), salinity, waterlogging, and the combined salinity‐waterlogging stress during the germination and seedling stage (six weeks) in pots in a greenhouse. Data including shoot and root dry weight, root‐to‐shoot dry weight ratio, root length, and specific root length were analyzed. Salinity‐waterlogging reduced dry weight of both shoots (556.1 mg) and roots (269.4 mg) compared with the controls (1295.1 and 686.7 mg) (P &lt; .0001). The control plants had a root‐to‐shoot dry weight ratio of 52.9%, higher than the salinity‐treated ones (44.1%) (P = .0017). Root length was higher in the control and waterlogged plants than salinity and salinity‐waterlogged plants. Saline‐waterlogged and control plants had the highest and lowest specific root length, respectively. Among the Kentucky bluegrass cultivars, Sudden Impact, Award, Limousine, and Kenblue had higher tissue biomass, followed by America, Legend, and Arrowhead, whereas Moonlight and Blue Note performed poorly. Blue Note had a higher specific root length than all other grasses, except Moonlight. It may be a better management practice to use cultivars such as Sudden Impact, Award, Limousine, and Kenblue, which appear from this research to be relatively tolerant to salinity/waterlogging stress, when establishing a new turf surface under the aforementioned stresses.

Predicting Cool‐Season Turfgrass Response with Solvita Soil Tests, Part 2: CO2–Burst Carbon Concentrations

Current turfgrass fertilizer recommendations do not account for plant‐available soil N mineralized from labile C fractions. The Solvita Soil CO2–Burst (SSCB) test can measure mineralizable C via soil CO2 respiration. This study was conducted across 3 yr (2014–2016) in Connecticut to determine: (i) if SSCB–C concentrations are correlated to responses from predominately Kentucky bluegrass (Poa pratensis L.) and tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] lawns, and (ii) the probability of turfgrass responses being equal to or greater than responses from common urea rates in relation to SSCB–C concentrations. Randomized complete block design field experiments were set out with 23 rates of organic fertilizer (0–2000 kg N ha−1 yr−1) and four different rates of urea (50, 100, 150, and 200 kg N ha−1 yr−1). Yearly spring soil samples were analyzed for SSCB–C concentrations and correlated with turfgrass responses. Growth and quality responded positively and linearly (P &lt; 0.001) to SSCB–C concentrations, but variability was high and correlations were relatively weak. When spring soil SSCB–C concentrations were ≥91, 113, 166, and 211 mg kg−1, there was a ≥90% probability that overall combined responses across species and variables would be equal to or greater than responses obtained from urea rates of 50, 100, 150, and 200 kg N ha−1 yr−1, respectively. The SSCB test has promise for predicting the probability of soils supporting turfgrass whose performance equals or exceeds benchmark values. This would be helpful in guiding N fertilization, but high variability within the test may limit its predictive ability.

Predicting Cool‐Season Turfgrass Response with Solvita Soil Tests, Part 1: Labile Amino‐Nitrogen Concentrations

ABSTRACTCurrent turfgrass fertilizer recommendations do not account for potential mineralizable N in the soil. The Solvita Soil Labile Amino‐Nitrogen (SLAN) test measures a labile fraction of soil N. This study was conducted across 9 yr (2008–2016) in Connecticut to determine if responses from predominately Kentucky bluegrass (Poa pratensis L.) and tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] lawns are correlated to SLAN–N concentrations, and to determine the probability of turfgrass responses equaling or exceeding the response from benchmark urea rates in relation to SLAN–N concentrations. Randomized complete block design field experiments were set out with 23 rates of an organic fertilizer (0–2000 kg N ha−1 yr−1) and four different rates of urea (50, 100, 150, and 200 kg N ha−1 yr−1). Yearly spring soil samples were analyzed for SLAN–N concentrations, and turfgrass growth and quality responses were collected during the growing seasons. Turfgrass responded positively and linearly (P &lt; 0.001) to SLAN–N concentrations, but correlations were relatively weak to moderate. When spring soil SLAN–N concentrations were ≥158, 165, 198, and 217 mg kg−1, there was a ≥90% probability that overall combined responses across species and measured variables would be equal to or greater than responses obtained from 50, 100, 150, and 200 kg urea N ha−1 yr−1, respectively. The SLAN test has promise as an objective soil test to categorize the N fertilization response potential of turfgrass soils, and this would be helpful in guiding N fertilization.

Models of turfgrass seed germination related to water content.

Turfgrasses have been widely utilized by humans to enhance the environment for more than several centuries. Seed germination is of great importance in the development of the turfgrass industry. In this study, the seed germination models of the responses of three types of turfgrasses to water were studied. The results indicated that irrigation water was mainly related to the variation of seed volume rather than a fixed value in this experiment. The maximum k value of tall fescue, Kentucky bluegrass and perennial ryegrass is 1.1548, 1.6946 and 4.0940, respectively. The optimal value of k is 1.0617 for tall fescue, 1.4610 for Kentucky bluegrass, and 1.6614 for perennial ryegrass. Perennial ryegrass seeds are more sensitive to water than those of tall fescue and Kentucky bluegrass, and this turfgrass is the fastest to reach the maximum value of the germination rate. Based on the results from the present experiment, the seed germination function can describe the response of turfgrass seed germination to external water content variation and their sensitivities. The function obtained could be used to perform quantitative studies on the dynamic changes of seed germination under different water conditions that will contribute to improved predictions of the optimal fitting curves of the germination over a range of water.

Alleviation of Drought Stress in Turfgrass by the Combined Application of Nano-compost and Microbes from Compost

Drought stress is a key environmental factor limiting the growth and productivity of plants. Turfgrasses are often affected by drought in north China due to water shortage. In the present study, the impact of nanosized compost either alone or in combination with drought tolerant isolates from compost on turfgrass response to drought was investigated. Municipal solid waste (MSW) compost was processed into nanosized particles and added in turfgrass soil. Microorganisms in the MSW compost were screened for drought stress tolerance using increasing concentrations of polyethylene glycol (PEG 6000). Festuca arundinacea Schreb. plants were inoculated with this mixture and exposed to drought stress by reducing the amount of water added at vegetative growth stage. The drought-tolerant isolates from compost were identified as Bacillus cereus, Lysinibacillus sp. and Rhodotorula glutinis. Our results revealed that nanocompost and microbial inoculation minimized the drought stress-imposed effects significantly increasing shoot biomass, root biomass, and chlorophyll content. Similarly, nanocompost-treated and inoculated seedlings showed higher levels of antioxidant enzymes and lower MDA content compared to nontreated control under drought stress. The combination of nano-sized compost and microbial inoculation were more efficient than nanocompost alone in terms of influencing growth and physiological status of the seedlings under drought stress. Our data suggest that nanocompost combined with drought-tolerant isolates may enhance drought tolerance in turfgrass by promoting plant growth and increasing the capacity to eliminate toxic reactive oxygen species (ROS).

Balancing substrate depth and irrigation inputs influence the aesthetic quality ofPaspalum vaginatumwhen grown on adaptive extensive green roof systems

Turfgrass use on extensive green roofs could offer a sustainable solution for increasing urban greening within the existing built space in contemporary cities. The aim of the study was to determine Paspalum vaginatum 'Platinum TER' drought tolerance when grown under extensive green roof conditions and two irrigation regimes. Treatments included: (i) six extensive green roof substrates formulated from mixing locally available materials; (ii) two substrate depths (7.5 or 15 cm) and (iii) two irrigation regimes (60% ETc or 100% ETc). Turfgrass drought tolerance was measured, using digital image analysis, as the number of days until a treatment reached 50% green turf cover (GTC). In both study years (2011 and 2012), for each one of the six substrate types, higher GTC values were reached when deeper profiles (15 cm) were combined with the higher irrigation regime (100% ETc), while the worst drought tolerance turfgrass response was obtained when the swallow substrate (7.5 cm) was combined with the deficit irrigation regime of 60% ETc. It was found that increasing substrate depth resulted in delay of drought stress symptoms expression, while irrigation regime affected the velocity of GTC reduction over time with lower irrigation regime resulting in faster GTC decline compared to higher irrigation regime. It was also concluded that the imposed drought stress to the turfgrass by the reduced irrigation could be compensated by increasing substrate depth. Thus, in buildings with adequate load bearing capacity, it is preferable to select a substrate depth of 15 cm since it will result in 40% reduction on irrigation inputs compared to substrate depth of 7.5 cm.