Long-term effects of clipping and nitrogen management in turfgrass on soil organic carbon and nitrogen dynamics: the CENTURY model simulation

Influence of urban land use types on ecosystem services in two rapidly urbanizing cities of southwestern Nigeria

Many ecological functions in cities are based on urban soils. In order to meet the needs of the expanding human population and the ensuing strain on natural resources, it is essential for soil-based ecosystems to function. Approximately 80% of the total urban land use in Akure and Okitipupa, Nigeria, are used for commercial, residential, and agricultural purposes. Thus, we investigated the potential of these three urban land use types (ULUTs) to offer a variety of ecosystem services in the two different cities. Soil properties that serve as proxy indicators for four ecosystem services were measured in the ULUTs: hydraulic conductivity (Kunsat) and available soil water for rainwater retention; soil organic carbon (SOC) stock for carbon storage; soil microbial respiration (SMR) for the capacity to support biological activity; and soil compaction (PR) and total nitrogen (TN) for promoting plant growth. The location and ULUT resulted in distinct ecosystem service provisioning. In comparison to Akure, Okitipupa soils had lower PR (1.0 vs 1.1 MPa) but higher Kunsat (36.9 vs 10.3 cm h-1), SOC stock (6.9 vs 5.7 Mg C ha-1), and SMR levels (35.2 vs 23.6 mg CO2-C g-1 soil). Commercial soils exhibited more compaction than residential and agricultural soils but less SOC stock and Kunsat, and TN in both locations. The properties of the urban soils showed that the soils could support a variety of ecosystem services. Different soil properties at the city level led to variations in the potential for ecosystem services in various locations, and these variations were observable in commercial, residential, and agricultural soils. Understanding urban soils would thus necessitate both cross-city comparative studies as well as within-city examinations of the potential for ecosystem services for various urban land use types.

High soil carbon sequestration rates persist several decades in turfgrass systems: A meta-analysis

Managed turfgrass is a common component of urban landscapes that is expanding under current land use trends. Previous studies have reported high rates of soil carbon sequestration in turfgrass, but no systematic review has summarized these rates nor evaluated how they change as turfgrass ages. Here we conducted a meta-analysis of soil carbon sequestration rates from 63 studies globally, comprised mostly of C3 grass species in the U.S., including 24 chronosequence studies that evaluated carbon changes over 75 years or longer. We showed that turfgrass established within the last ten years had a positive mean soil C sequestration rate of 5.3 Mg CO₂ ha^-1 yr^-1 (95% CI = 3.7-6.2), which is higher than rates reported for several soil conservation practices. Areas converted to turfgrass from forests were an exception, sometimes lost soil carbon, and had a cross-study mean sequestration rate that did not differ from 0. In some locations, soil C accumulated linearly with turfgrass age over several decades, but the major trend was for soil C accumulation rates to decline through time, reaching a cross-study mean sequestration rate that was not different from 0 at 50 years. We show that fitting soil C timeseries with a mechanistically derived function rather than purely empirical functions did not alter these conclusions, nor did employing equivalent soil mass versus fixed-depth carbon stock accounting. We conducted a partial greenhouse gas budget that estimated emissions from mowing, N-fertilizer production, and soil N₂O emissions. When N fertilizer was applied, average maintenance emissions offset 32% of C sequestration in recently established turfgrass. Potential emission removals by turfgrass can be maximized with reduced-input management. Management decisions that avoid losing accrued soil C-both when turfgrass is first established and when it is eventually replaced with other land-uses-will also help maximize turfgrass C sequestration potential.

Carbon Sequestration in Turfgrass–Soil Systems

Plants are key components of the terrestrial ecosystem carbon cycle. Atmospheric CO₂ is assimilated through photosynthesis and stored in plant biomass and in the soil. The use of turfgrass is expanding due to the increasing human population and urbanization. In this review, we summarize recent carbon sequestration research in turfgrass and compare turfgrass systems to other plant systems. The soil organic carbon (SOC) stored in turfgrass systems is comparable to that in other natural and agricultural systems. Turfgrass systems are generally carbon-neutral or carbon sinks, with the exception of intensively managed areas, such as golf course greens and athletic fields. Turfgrass used in other areas, such as golf course fairways and roughs, parks, and home lawns, has the potential to contribute to carbon sequestration if proper management practices are implemented. High management inputs can increase the biomass productivity of turfgrass but do not guarantee higher SOC compared to low management inputs. Additionally, choosing the appropriate turfgrass species that are well adapted to the local climate and tolerant to stresses can maximize CO₂ assimilation and biomass productivity, although other factors, such as soil respiration, can considerably affect SOC. Future research is needed to document the complete carbon footprint, as well as to identify best management practices and appropriate turfgrass species to enhance carbon sequestration in turfgrass systems.

Contribution of grass clippings to turfgrass fertilization and soil water content under four nitrogen levels

Returning turfgrass clippings to soil (i.e., mulching) has been shown to yield many benefits, such as reducing fertilizer requirements. However, previous reports on the contribution of clippings to turfgrass fertilization varies widely, making it difficult for turfgrass managers to adjust their fertilization practices. Other potential benefits of this practice, such as soil water conservation, still need to be quantified. The objectives of this project were to measure the contribution of Kentucky bluegrass clippings to N, P and K fertilization under four different N levels and to measure the impact of clippings management on turfgrass color (NDVI), soil nutrient and water content as well as thatch accumulation. A field experiment was conducted over three years, with treatments consisting of two clipping management strategies (returned or removed) and four nitrogen levels (0, 48, 96 and 144 kg N ha -1 yr -1). Clippings were collected on every mowing date and were analyzed for N, P and K foliar content. Soil volumetric water content and NDVI were measured weekly, while thatch accumulation and soil chemical content (Mehlich-3) were assessed twice per year. Increasing N fertilization resulted in an increase in both clippings dry matter yield (DMY) and foliar N concentration. Returning grass clippings was equivalent to doubling the amount of N applied through the fertilizer and resulted in an increase in turfgrass color and soil P and K levels. For P and K, clippings contribution was more affected by their DMY than by foliar concentrations. Grass clippings did not contribute to thatch accumulation, but resulted in a consistent increase (3.9% on average) in soil volumetric water content.

Urban net primary production: Concepts, field methods, and Baltimore, Maryland, USA case study

Given the large and increasing amount of urban, suburban, and exurban land use on Earth, there is a need to accurately assess net primary productivity (NPP) of urban ecosystems. However, the heterogeneous and dynamic urban mosaic presents challenges to the measurement of NPP, creating landscapes that may appear more similar to a savanna than to the native landscape replaced. Studies of urban biomass have tended to focus on one type of vegetation (e.g., lawns or trees). Yet a focus on the ecology of the city should include the entire urban ecosystem rather than the separate investigation of its parts. Furthermore, few studies have attempted to measure urban aboveground NPP (ANPP) using field-based methods. Most studies project growth rates from measurements of tree diameter to estimate annual ANPP or use remote sensing approaches. In addition, field-based methods for measuring NPP do not address any special considerations for adapting such field methods to urban landscapes. Frequent planting and partial or complete removal of herbaceous and woody plants can make it difficult to accurately quantify increments and losses of plant biomass throughout an urban landscape. In this study, we review how ANPP of urban landscapes can be estimated based on field measurements, highlighting the challenges specific to urban areas. We then estimated ANPP of woody and herbaceous vegetation over a 15-year period for Baltimore, MD, USA using a combination of plot-based field data and published values from the literature. Baltimore's citywide ANPP was estimated to be 355.8 g m^-2 , a result that we then put into context through comparison with other North American Long-Term Ecological Research (LTER) sites and mean annual precipitation. We found our estimate of Baltimore citywide ANPP to be only approximately half as much (or less) than ANPP at forested LTER sites of the eastern United States, and more comparable to grassland, oldfield, desert, or boreal forest ANPP. We also found that Baltimore had low productivity for its level of precipitation. We conclude with a discussion of the significance of accurate assessment of primary productivity of urban ecosystems and critical future research needs.

Bermudagrass Cultivars with Different Tolerance to Nematode Damage Are Characterized by Distinct Fungal but Similar Bacterial and Archaeal Microbiomes

Turfgrass landscapes have expanded rapidly in recent decades and are a major vegetation type in urbanizing ecosystems. While turfgrass areas provide numerous ecosystem services in urban environments, ecological side effects from intensive management are raising concerns regarding their sustainability. One potentially promising approach to ameliorate the ecological impact and decrease the use of agricultural chemicals is to take advantage of naturally evolved turfgrass-associated microbes by harnessing beneficial services provided by microbiomes. Unfortunately, especially compared to agricultural crops, the microbiomes of turfgrasses are not well understood. Here, we analyzed microbial communities inhabiting the leaf and root endospheres as well as soil in two bermudagrass cultivars, ‘Latitude 36’ and ‘TifTuf’, which exhibit distinct tolerance to nematode damage, with the goal of identifying potential differences in the microbiomes that might explain their distinct phenotype. We used 16S rRNA gene V4 and ITS2 amplicon sequencing to characterize the microbiomes in combination with microbial cultivation efforts to identify potentially beneficial endophytic fungi and bacteria. Our results show that Latitude 36 and TifTuf showed markedly different fungal microbiomes, each harboring unique taxa from Ascomycota and Glomeromycota, respectively. In contrast, less difference was observed from bacterial and archaeal microbiomes, which were dominated by Bacteroidetes and Thaumarchaeota, respectively. The TifTuf microbiomes exhibited lower microbial diversity compared to Latitude 36. Many sequences could not be classified to a higher taxonomic resolution, indicating a relatively high abundance of hitherto undescribed microorganisms. Our results provide new insights into the structure and composition of turfgrass microbiomes but also raise important questions regarding the functional attributes of key taxa.

Creeping Bentgrass Yield Prediction With Machine Learning Models

Nitrogen is the most limiting nutrient for turfgrass growth. Instead of pursuing the maximum yield, most turfgrass managers use nitrogen (N) to maintain a sub-maximal growth rate. Few tools or soil tests exist to help managers guide N fertilizer decisions. Turf growth prediction models have the potential to be useful, but the currently existing turf growth prediction model only takes temperature into account, limiting its accuracy. This study developed machine-learning-based turf growth models using the random forest (RF) algorithm to estimate short-term turfgrass clipping yield. To build the RF model, a large set of variables were extracted as predictors including the 7-day weather, traffic intensity, soil moisture content, N fertilization rate, and the normalized difference red edge (NDRE) vegetation index. In this study, the data were collected from two putting greens where the turfgrass received 0 to 1,800 round/week traffic rates, various irrigation rates to maintain the soil moisture content between 9 and 29%, and N fertilization rates of 0 to 17.5 kg ha^-1 applied biweekly. The RF model agreed with the actual clipping yield collected from the experimental results. The temperature and relative humidity were the most important weather factors. Including NDRE improved the prediction accuracy of the model. The highest coefficient of determination (R²) of the RF model was 0.64 for the training dataset and was 0.47 for the testing data set upon the evaluation of the model. This represented a large improvement over the existing growth prediction model (R ² = 0.01). However, the machine-learning models created were not able to accurately predict the clipping production at other locations. Individual golf courses can create customized growth prediction models using clipping volume to eliminate the deviation caused by temporal and spatial variability. Overall, this study demonstrated the feasibility of creating machine-learning-based yield prediction models that may be able to guide N fertilization decisions on golf course putting greens and presumably other turfgrass areas.

Greenhouse gas fluxes from turfgrass systems: Species, growth rate, clipping management, and environmental effects

Turfgrass systems can be an important source or sink for greenhouse gases (GHG), including carbon dioxide (CO₂ ), nitrous oxide (N₂ O), and methane (CH₄ ). Further research is required in turfgrass systems; therefore, our objectives were to evaluate the effects of turfgrass species, growth rate, clipping management, and environmental conditions on GHG emissions. Greenhouse gas fluxes were measured in two separate field experiments in West Lafayette, IN. Experiment 1 investigated GHG flux in three cool-season (C₃ ) and two warm-season (C₄ ) turfgrass species during two growing seasons. Experiment 2 investigated fluxes in two C₃ cultivars with varying growth rates and under different clipping management regimes. The C₃ turfgrasses had the highest mean CO₂ flux rates ranging from 0.373 to 0.431 g CO₂ -C m^-2 h^-1 compared with 0.273 to 0.361 g CO₂ -C m^-2 h^-1 for C₄ turfgrasses. Mean hourly N₂ O flux rates ranged from 43.3 to 50.9 μg N₂ O-N m^-2 h^-1 for C₃ compared with 11.1 to 14.4 μg N₂ O-N m^-2 h^-1 for C₄ turfgrasses. Methane flux was more variable across time, but overall C₄ turfgrasses were more likely to be a CH₄ source, whereas C₃ turfgrasses were often a CH₄ sink. Growth rate and grass clipping management treatments had negligible impact on measured GHG flux. The differences in management practices specific to C₃ and C₄ turfgrasses had the largest impact on GHG flux. Results indicate the impact and importance of turfgrass species selection on GHG flux and also provide more information on our overall understanding on carbon and nitrogen cycling in urban soils.

Effect of Biowastes on Soil Remediation, Plant Productivity and Soil Organic Carbon Sequestration: A Review

High anthropogenic activities are constantly causing increased soil degradation and thus soil health and safety are becoming an important issue. The soil quality is deteriorating at an alarming rate in the neighborhood of smelters as a result of heavy metal deposition. Organic biowastes, also produced through anthropogenic activities, provide some solutions for remediation and management of degraded soils through their use as a substrate. Biowastes, due to their high content of organic compounds, have the potential to improve soil quality, plant productivity, and microbial activity contributing to higher humus production. Biowaste use also leads to the immobilization and stabilization of heavy metals, carbon sequestration, and release of macro and micronutrients. Increased carbon sequestration through biowaste use helps us in mitigating climate change and global warming. Soil amendment by biowaste increases soil activity and plant productivity caused by stimulation in shoot and root length, biomass production, grain yield, chlorophyll content, and decrease in oxidative stress. However, biowaste application to soils is a debatable issue due to their possible negative effect of high heavy metal concentration and risks of their accumulation in soils. Therefore, regulations for the use of biowastes as fertilizer or soil amendment must be improved and strictly employed to avoid environmental risks and the entry of potentially toxic elements into the food chain. In this review, we summarize the current knowledge on the effects of biowastes on soil remediation, plant productivity, and soil organic carbon sequestration.

Impact of urbanization on soil loss: a case study from sod production

The rapidly increasing population of urban centers leads to the increasing need for greenspaces. Sodding of turfgrass provides instant greenspace, but it removes soil from sod farms. The extent of such removal has not been widely quantified. The amount quantity of soil and organic matter lost with sod harvest and the associated cost of nutrients lost from six sod farms in the Marmara region of Turkey were determined. Soil loss ranged from 166 to 243 Mg ha^-1 year^-1, while the associated organic matter loss ranged from 1 to 6 Mg ha^-1 year^-1. The amount of soil loss increased with increases in gravimetric water, clay, and silt contents, and duration under sod harvest, while it decreased with an increase in sand content. Annual nutrient lost ranged from 117 to 449 kg ha^-1 for N, from 2 to 18 kg ha^-1 for P₂O₅, and from 21 to 175 kg ha^-1 for K₂O. Replacing the nutrient lost would cost about $134 ha^-1 year^-1 for sandy soils and $444 ha^-1 year^-1 for fine-textured soils. Soil lost with sod harvest was 134 times higher than that from agricultural lands by erosion in the region, although the area under sod production is much smaller than that under croplands. Similarly, organic matter loss was 4 to 5 times higher than the accumulation rate under established turfgrass in golf courses and lawns in locations with similar climate. Overall, sod harvesting results in significant and costly soil, organic matter, and nutrient loss, which, although small in area, can be an important component of total soil erosion.

Plant production decreases whereas nutrients concentration increases in response to the decrease of mowing stubble height

Mowing is a common practice in grassland management. It removes the majority of current year's aboveground plant biomass and thus substantial amounts of nutrients residing in plant tissues. The responses of plant aboveground biomass and nutrients to mowing stubble height is of great importance for developing sustainable mowing regimes, however, they are not well understood. We studied the effects of 4-year annual mowing at different height on plant aboveground biomass, plant N, P and N:P ratio, and soil nutrients in an Inner Mongolian steppe. Six stubble heights were set respectively at 14 cm (M14), 12 cm (M12), 10 cm (M10), 8 cm (M8), 6 cm (M6) and less than 0.3 cm (M0) height to ground surface. A no-mowing treatment (CK) was also included, making seven treatments. The results show that plant biomass production increased under light mowing (stubble height  > 12 cm) but decreased under heavy mowing (stubble height  < 6 cm), and the optimal stubble height for sustainable mowing was 6-12 cm. Plant N and P concentrations increased with mowing intensity (i.e. with the decrease of mowing stubble height). Plant N:P ratio decreased for some species, but no a directional change was detected in plant N:P ratio at the community level, nor in soil organic carbon and nutrient concentrations across the stubble height treatments. Our results indicate that plant biomass and N & P respond quickly to mowing height, whereas the response of soil chemical properties is insignificant over the 4-year period. To elucidate variation of species compensatory growth along mowing intensity gradient and the mutual feedback mechanism of soil-plant in mowing grassland, long-term study at permanent sites with changing stubble heights should be strengthened.

Deficit Irrigation and Fertility Effects on NO3-N Exports from St. Augustinegrass

Proper management of turfgrass systems is critical for reducing the risk of nutrient loss and protecting urban surface waters. In the southern United States, irrigation can be the most significant management practice regulating the biogeochemical and hydrological cycles of turfgrass systems. A turfgrass runoff research facility was used to assess the effects of deficit irrigation and fertilizer applications on turfgrass canopy cover and nitrate-N (NO-N) exports in runoff from St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] turf over a 2-yr period. Treatments were arranged as a randomized complete block design having eight combinations of irrigation (100, 75, or 50% of estimated turfgrass water requirements) and fertility level (0, 88, and 176 kg N ha yr). Runoff from 31 rainfall events and one irrigation excess event were used to estimate annual and seasonal NO-N exports. The majority of annual NO-N exports occurred during the late winter and spring. Deficit irrigation reduced summer and early autumn runoff volumes. Lower summer and autumn runoff volumes (from deficit irrigation) coincided with reduced NO-N exports from runoff during Year 1. Deficit irrigation combined with fertilizer applications increased runoff [NO-N] in Year 2, suggesting that the previous year's export reduction contributed to higher N accumulation in the system and thus a higher N loss potential. These findings suggest that deficit irrigation can be a tool for reducing seasonal nutrient exports from St. Augustinegrass lawns so long as fertilizer inputs are moderate.

Agroforestry: a sustainable environmental practice for carbon sequestration under the climate change scenarios-a review

Agroforestry is a sustainable land use system with a promising potential to sequester atmospheric carbon into soil. This system of land use distinguishes itself from the other systems, such as sole crop cultivation and afforestation on croplands only through its potential to sequester higher amounts of carbon (in the above- and belowground tree biomass) than the aforementioned two systems. According to Kyoto protocol, agroforestry is recognized as an afforestation activity that, in addition to sequestering carbon dioxide (CO₂) to soil, conserves biodiversity, protects cropland, works as a windbreak, and provides food and feed to human and livestock, pollen for honey bees, wood for fuel, and timber for shelters construction. Agroforestry is more attractive as a land use practice for the farming community worldwide instead of cropland and forestland management systems. This practice is a win-win situation for the farming community and for the environmental sustainability. This review presents agroforestry potential to counter the increasing concentration of atmospheric CO₂ by sequestering it in above- and belowground biomass. The role of agroforestry in climate change mitigation worldwide might be recognized to its full potential by overcoming various financial, technical, and institutional barriers. Carbon sequestration in soil by various agricultural systems can be simulated by various models but literature lacks reports on validated models to quantify the agroforestry potential for carbon sequestration.

Drivers of soil and tree carbon dynamics in urban residential lawns: a modeling approach

Soils constitute the largest sink of terrestrial carbon (C), and urban soils have the potential to provide significant soil C storage. Soils in urbanized landscapes experience a multitude of human alterations, such as compaction and management subsidies, that impact soil C dynamics. While field studies may provide data on urban soil C storage, modeling soil C dynamics under various human impact scenarios will provide a basis for identifying drivers of urban soil C dynamics and for predicting the potential for these highly altered soils to store C over time intervals not typically amenable to empirical validation. The goal of this study was to model soil C dynamics in residential lawns using CENTURY, a dynamic mechanistic model, to determine whether drivers of soil C dynamics in natural systems (e.g., soil texture) were equally useful for estimating soil C content of highly modified soils in urban residential areas. Without incorporating human impacts, we found no relationship between initial CENTURY model simulations and observed soil C (P > 0.05). Factors that best explained soil C accumulation for the observed soil C (bulk density, r²  = 0.30; home age, r²  = 0.37; P < 0.01) differed from those found important for the CENTURY model simulations (percent sand, r²  = 0.72, P < 0.001). Therefore, we conducted a modeling exercise to test whether simulating potential construction disturbance and lawn management practices would improve modeled soil and tree C. We found that incorporating these factors did improve CENTURY's ability to model soil and tree C (P < 0.001). The results from this analysis suggest that incorporating various human disturbances and management practices that occur in urban landscapes into CENTURY model runs will improve its ability to predict urban soil C dynamics, at least within a 100-yr time frame. Thus, enhancing our ability to provide recommendations for management and development practices that result in increasing urban soil C storage.

Persistence in and Release of 2,4-D and Azoxystrobin from Turfgrass Clippings

Research has shown that pesticide residue in clippings from previously treated turfgrass may become bioavailable as grass decomposes, adversely affecting off-target organisms. We conducted a field study to quantify 2,4-D (2,4-dichlorophenoxyacetic acid) and azoxystrobin (methyl(E)-2-{2[6-(2-cyanophenoxy)pyrmidin-4-yloxy]phenyl}-3-methoxyacrylate) residues in turfgrass clippings collected from hybrid bermudagrass [ (L.) Pers. × Burtt-Davy], tall fescue [ (Schreb.) S.J. Darbyshire], and zoysiagrass ( Steud.). A subsequent greenhouse experiment was conducted to measure pesticide release from clippings into water. 2,4-D (1.6 kg a.i. ha) and azoxystrobin (0.6 kg a.i. ha) were applied to field plots at 32, 16, 8, 4, 2, 1, or 0 d before collection of the clippings. Clippings were collected from each experimental unit to quantify pesticide release from clippings into water. Both 2,4-D and azoxystrobin were detected when turfgrass was treated over the 32-d experimental period, suggesting that clipping management should be implemented for an extended period of time after application. Pesticide residue was detected in all water samples collected, confirming 2,4-D and azoxystrobin release from turfgrass clippings; however, pesticide release varied between compounds. Two days after clippings were incorporated in water, 39 and 10% of 2,4-D and azoxystrobin were released from clippings, respectively. Our research supports the currently recommended practice of returning clippings to the turfgrass stand when mowing because removal of 2,4-D and azoxystrobin in clippings may reduce pest control and cause adverse off-target impacts.

Nitrous Oxide Emissions from a Golf Course Fairway and Rough after Application of Different Nitrogen Fertilizers

Few studies have quantified nitrous oxide (NO) emissions from intensively managed turfgrass systems on golf courses. Fertilizer treatments consisting of urea with inhibitors of nitrification and urease (INU), polymer-coated urea (PCU), and uncoated balanced methylene urea (BMU) chain, which use different mechanisms to control the release of N substrate, were applied to a golf course fairway and rough three times during the 2011 growing season at a rate of 50 kg N ha per application. The vented chamber method was used to measure turf-soil-atmospheric NO exchange. Cumulative emissions from fairway INU, PCU, and BMU treatments totaled 6.5, 1.9, and 7.6 kg NO-N ha yr, representing a 4.02, 1.25, and 4.75% loss of total N applied, respectively. Summer INU and BMU fertilization to the fairway produced the greatest NO fluxes. Rapid fluxes during the summer were likely related to low physiological activity in cool-season turfgrass and to warm, wet soil conditions that increased denitrification rates. However, PCU applied to the fairway was more resistant to NO losses than other fertilizer treatments. Fertilizer treatments applied to the rough had cumulative emissions of 2.4, 1.50, and 1.49 kg NO-N ha yr from INU, PCU, and BMU treatments, corresponding to a 1.21, 0.62, and 0.61% loss of total N applied, respectively. The lower NO emission on roughs was likely associated with greater carbon pools, lower soil moisture, and lower temperatures. This study supports the effectiveness of PCU to reduce NO emission from cool-season turfgrass fairways when soil conditions favored denitrification during warm periods. Applying INU and BMU when soil was cool and dry was effective in moderating NO losses.

Carbon fluxes from an urban tropical grassland

Turfgrass covers a large fraction of the urbanized landscape, but the carbon exchange of urban lawns is poorly understood. We used eddy covariance and flux chambers in a grassland field manipulative experiment to quantify the carbon mass balance in a Singapore tropical turfgrass. We also assessed how management and variations in environmental factors influenced CO2 respiration. Standing aboveground turfgrass biomass was 80 gC m(-2), with a mean ecosystem respiration of 7.9 ± 1.1 μmol m(-2) s(-1). The contribution of autotrophic respiration was 49-76% of total ecosystem respiration. Both chamber and eddy covariance measurements suggest the system was in approximate carbon balance. While we did not observe a significant relationship between the respiration rates and soil temperature or moisture, daytime fluxes increased during the rainy interval, indicating strong overall moisture sensitivity. Turfgrass biomass is small, but given its abundance across the urban landscape, it significantly influences diurnal CO2 concentrations.

The effects of household management practices on the global warming potential of urban lawns

Nitrous oxide (N2O) emissions are an important component of the greenhouse gas (GHG) budget for urban turfgrasses. A biogeochemical model DNDC successfully captured the magnitudes and patterns of N2O emissions observed at an urban turfgrass system at the Richland Creek Watershed in Nashville, TN. The model was then used to study the long-term (i.e. 75 years) impacts of lawn management practice (LMP) on soil organic carbon sequestration rate (dSOC), soil N2O emissions, and net Global Warming Potentials (net GWPs). The model simulated N2O emissions and net GWP from the three management intensity levels over 75 years ranged from 0.75 to 3.57 kg N ha(-1)yr(-1) and 697 to 2443 kg CO2-eq ha(-1)yr(-1), respectively, which suggested that turfgrasses act as a net carbon emitter. Reduction of fertilization is most effective to mitigate the global warming potentials of turfgrasses. Compared to the baseline scenario, halving fertilization rate and clipping recycle as an alternative to synthetic fertilizer can reduce net GWPs by 17% and 12%, respectively. In addition, reducing irrigation and mowing are also effective in lowering net GWPs. The minimum-maintenance LMP without irrigation and fertilization can reduce annual N2O emissions and net GWPs by approximately 53% and 70%, respectively, with the price of gradual depletion of soil organic carbon, when compared to the intensive-maintenance LMP. A lawn age-dependent best management practice is recommended: a high dose fertilizer input at the initial stage of lawn establishment to enhance SOC sequestration, followed by decreasing fertilization rate when the lawn ages to minimize N2O emissions. A minimum-maintained LMP with clipping recycling, and minimum irrigation and mowing, is recommended to mitigate global warming effects from urban turfgrass systems. Among all practices, clipping recycle may be a relatively malleable behavior and, therefore, a good target for interventions seeking to reduce the environmental impacts of lawn management through public education. Our results suggest that a long-term or a chronosequence study of turfgrasses with varying ages is warranted to capture the complete dynamics of contribution of turfgrasses to global warming.

Simulation of Nitrous Oxide Emissions and Estimation of Global Warming Potential in Turfgrass Systems Using the DAYCENT Model

Nitrous oxide (NO) emissions are an important component of the greenhouse gas budget for turfgrasses. To estimate NO emissions and global warming potential, the DAYCENT ecosystem model was parameterized and applied to turfgrass ecosystems. The annual cumulative NO emissions predicted by the DAYCENT model were close to the measured emission rates of Kentucky bluegrass ( L.) sites in Colorado (within 16% of the observed values). For the perennial ryegrass ( L.) site in Kansas, the DAYCENT model initially overestimated the NO emissions for all treatments (urea and ammonium sulfate at 250 kg N ha yr and urea at 50 kg N ha yr) by about 200%. After including the effect of biological nitrification inhibition in the root exudate of perennial ryegrass, the DAYCENT model correctly simulated the NO emissions for all treatments (within 8% of the observed values). After calibration and validation, the DAYCENT model was used to simulate NO emissions and carbon sequestration of a Kentucky bluegrass lawn under a series of management regimes. The model simulation suggested that gradually reducing fertilization as the lawn ages from 0 to 50 yr would significantly reduce long-term NO emissions by approximately 40% when compared with applying N at a constant rate of 150 kg N ha yr. Our simulation indicates that a Kentucky bluegrass lawn in Colorado could change from a sink to a weak source of greenhouse gas emissions 20 to 30 yr after establishment.

Techno-ecological synergy as a path toward sustainability of a North American residential system

For any human-designed system to be sustainable, ecosystem services that support it must be readily available. This work explicitly accounts for this dependence by designing synergies between technological and ecological systems. The resulting techno-ecological network mimics nature at the systems level, can stay within ecological constraints, and can identify novel designs that are economically and environmentally attractive that may not be found by the traditional design focus on technological options. This approach is showcased by designing synergies for a typical American suburban home at local and life cycle scales. The objectives considered are carbon emissions, water withdrawal, and cost savings. Systems included in the design optimization include typical ecosystems in suburban yards: lawn, trees, water reservoirs, and a vegetable garden; technological systems: heating, air conditioning, faucets, solar panels, etc.; and behavioral variables: heating and cooling set points. The ecological and behavioral design variables are found to have a significant effect on the three objectives, in some cases rivaling and exceeding the effect of traditional technological options. These results indicate the importance and benefits of explicitly including ecosystems in the design of sustainable systems, something that is rarely done in existing methods.

Evaluating nutrient impacts in urban watersheds: challenges and research opportunities

This literature review focuses on the prevalence of nitrogen and phosphorus in urban environments and the complex relationships between land use and water quality. Extensive research in urban watersheds has broadened our knowledge about point and non-point pollutant sources, but the fate of nutrients is not completely understood. For example, it is not known how long-term nutrient cycling processes in turfgrass landscapes influence nitrogen retention rates or the relative atmospheric contribution to urban nitrogen exports. The effect of prolonged reclaimed water irrigation is also unknown. Stable isotopes have been used to trace pollutants, but distinguishing sources (e.g., fertilizers, wastewater, etc.) can be difficult. Identifying pollutant sources may aid our understanding of harmful algal blooms because the extent of the relationship between urban nutrient sources and algal blooms is unclear. Further research on the delivery and fate of nutrients within urban watersheds is needed to address manageable water quality impacts.

Lawn soil carbon storage in abandoned residential properties: an examination of ecosystem structure and function following partial human-natural decoupling

Residential abandonment is on the rise in many urban areas, with unknown implications for ecosystem structure and function on land slated for partial or full restoration to native habitat. Partial decoupling of human and natural systems could reduce disturbance (e.g., trampling, recreational traffic) and modify vegetation structure in a way that alters soil carbon storage, an ecosystem function that many municipalities consider a management objective of growing importance. We quantified soil carbon percent and mass to 10 cm depth and examined vegetation structure in 50 vacant and 10 occupied residential lawns located in Richmond, VA, with the principal objective of determining whether occupancy status alters trajectories of soil carbon storage or its correspondence with household economic/demographic indicators and vegetation cover. Abandoned residential lawns supported significantly less grass cover, but these declines were largely offset by increases in emergent overstory (>1 m height) vegetation cover. Soil carbon percent and mass did not differ between lawns of occupied and abandoned residences, even though significant, but highly uncertain, increases in soil carbon mass occurred in the first decade following vacancy. Instead, all residential lawns exhibited similar significant increases in soil carbon percent and mass with increasing residence age and neighborhood affluence, the former indicating annual carbon accretion rates of 20 g m(-2). We conclude that in this early stage of vacancy, soil carbon storage is already subtly responding to declines in human intervention, with reduced soil disturbance and sustained vegetation cover in abandoned lawns playing likely roles in emerging soil carbon storage trajectories.

Impacts of urbanization on carbon balance in terrestrial ecosystems of the Southern United States

Using a process-based Dynamic Land Ecosystem Model, we assessed carbon dynamics of urbanized/developed lands in the Southern United States during 1945-2007. The results indicated that approximately 1.72 (1.69-1.77) Pg (1P = 10(15)) carbon was stored in urban/developed lands, comparable to the storage of shrubland or cropland in the region. Urbanization resulted in a release of 0.21 Pg carbon to the atmosphere during 1945-2007. Pre-urbanization vegetation type and time since land conversion were two primary factors determining the extent of urbanization impacts on carbon dynamics. After a rapid decline of carbon storage during land conversion, an urban ecosystem gradually accumulates carbon and may compensate for the initial carbon loss in 70-100 years. The carbon sequestration rate of urban ecosystem diminishes with time, nearly disappearing in two centuries after land conversion. This study implied that it is important to take urbanization effect into account for assessing regional carbon balance.

Inconsistent definitions of "urban" result in different conclusions about the size of urban carbon and nitrogen stocks

There is conflicting evidence about the importance of urban soils and vegetation in regional C budgets that is caused, in part, by inconsistent definitions of "urban" land use. We quantified urban ecosystem contributions to C stocks in the Boston (Massachusetts, USA) Metropolitan Statistical Area (MSA) using several alternative urban definitions. Development altered aboveground and belowground C and N stocks, and the sign and magnitude of these changes varied by land use and development intensity. Aboveground biomass (live trees, dbh > or = 5 cm) for the MSA was 7.2 +/- 0.4 kg C/m2 (mean +/- SE), reflecting a high proportion of forest cover. Vegetation C was highest in forest (11.6 +/- 0.5 kg C/m2), followed by residential (4.6 +/- 0.5 kg C/m2), and then other developed (2.0 +/- 0.4 kg C/m2) land uses. Soil C (0-10 cm depth) followed the same pattern of decreasing C concentration from forest, to residential, to other developed land uses (4.1 +/- 0.1, 4.0 +/- 0.2, and 3.3 +/- 0.2 kg C/m2, respectively). Within a land use type, urban areas (which we defined as > 25% impervious surface area [ISA] within a 1-km(2) moving window) generally contained less vegetation C, but slightly more soil C, than nonurban areas. Soil N concentrations were higher in urban areas than nonurban areas of the same land use type, except for residential areas, which had similarly high soil N concentrations. When we compared our definition of urban to other commonly used urban extents (U.S. Census Bureau, Global Rural-Urban Mapping Project [GRUMP], and the MSA itself), we found that urban soil (1 m depth) and vegetation C stocks spanned a wide range, from 14.4 +/- 0.8 to 54.5 +/- 3.4 Tg C and from 4.2 +/- 0.4 to 27.3 +/- 3.2 Tg C, respectively. Conclusions about the importance of urban soils and vegetation to regional C and N stocks are very sensitive to the definition of urban used by the investigators. Urban areas, regardless of definition, are rapidly expanding in their extent; a systematic understanding of how our development patterns influence ecosystems is necessary to inform future development choices.

A model of greenhouse gas emissions from the management of turf on two golf courses

An estimated 32,000 golf courses worldwide (approximately 25,600 km2), provide ecosystem goods and services and support an industry contributing over $124 billion globally. Golf courses can impact positively on local biodiversity however their role in the global carbon cycle is not clearly understood. To explore this relationship, the balance between plant–soil system sequestration and greenhouse gas emissions from turf management on golf courses was modelled. Input data were derived from published studies of emissions from agriculture and turfgrass management. Two UK case studies of golf course type were used, a Links course (coastal, medium intensity management, within coastal dune grasses) and a Parkland course (inland, high intensity management, within woodland).Playing surfaces of both golf courses were marginal net sources of greenhouse gas emissions due to maintenance (Links −2.2 ± 0.4 Mg CO2e ha(−1) y(−1); Parkland − 2.0 ± 0.4 Mg CO2e ha(−1) y(−1)). A significant proportion of emissions were from the use of nitrogen fertiliser, especially on tees and greens such that 3% of the golf course area contributed 16% of total greenhouse gas emissions. The area of trees on a golf course was important in determining whole-course emission balance. On the Parkland course, emissions from maintenance were offset by sequestration from turfgrass, and trees which comprised 48% of total area, resulting in a net balance of −5.4 ± 0.9 Mg CO2e ha(−1) y(−1). On the Links course, the proportion of trees was much lower (2%) and sequestration from links grassland resulted in a net balance of −1.6 ± 0.3 Mg CO2e ha(−1) y(−1). Recommendations for golf course management and design include the reduction of nitrogen fertiliser, improved operational efficiency when mowing, the inclusion of appropriate tree-planting and the scaling of component areas to maximise golf course sequestration capacity. The findings are transferrable to the management and design of urban parks and gardens, which range between fairways and greens in intensity of management.

Denitrification in suburban lawn soils

There is great uncertainty about the fate of nitrogen (N) added to urban and suburban lawns. We used direct flux and in situ chamber methods to measure N and NO fluxes from lawns instrumented with soil O sensors. We hypothesized that soil O, moisture, and available NO were the most important controls on denitrification and that N and NO fluxes would be high following fertilizer addition and precipitation events. While our results support these hypotheses, the thresholds of soil O, moisture, and NO availability required to see significant N fluxes were greater than expected. Denitrification rates were high in saturated, fertilized soils, but low under all other conditions. Annual denitrification was calculated to be 14.0 ± 3.6 kg N ha yr, with 5% of the growing season accounting for >80% of the annual activity. Denitrification is thus an important means of removing reactive N in residential landscapes, but varies markedly in space, time, and with factors that affect soil saturation (texture, structure, compaction) and NO availability (fertilization). Rates of in situ NO flux were low; however, when recently fertilized soils saturated with water were incubated in the laboratory, we saw extraordinarily high rates of NO production for the first few hours of incubation, followed by rapid NO consumption later in the experiment. These findings indicate a lag time between accelerated NO production and counterbalancing increases in NO consumption; thus, we cannot yet conclude that lawns are an insignificant source of NO in our study area.

A model of greenhouse gas emissions from the management of turf on two golf courses

An estimated 32,000 golf courses worldwide (approximately 25,600 km(2)), provide ecosystem goods and services and support an industry contributing over $ 124 billion globally. Golf courses can impact positively on local biodiversity however their role in the global carbon cycle is not clearly understood. To explore this relationship, the balance between plant-soil system sequestration and greenhouse gas emissions from turf management on golf courses was modelled. Input data were derived from published studies of emissions from agriculture and turfgrass management. Two UK case studies of golf course type were used, a Links course (coastal, medium intensity management, within coastal dune grasses) and a Parkland course (inland, high intensity management, within woodland). Playing surfaces of both golf courses were marginal net sources of greenhouse gas emissions due to maintenance (Links 0.4 ± 0.1Mg CO(2)e ha(-1)y(-1); Parkland 0.7 ± 0.2Mg CO(2)e ha(-1)y(-1)). A significant proportion of emissions were from the use of nitrogen fertiliser, especially on tees and greens such that 3% of the golf course area contributed 16% of total greenhouse gas emissions. The area of trees on a golf course was important in determining whole-course emission balance. On the Parkland course, emissions from maintenance were offset by sequestration from trees which comprised 48% of total area, resulting in a net balance of -4.3 ± 0.9 Mg CO(2e) ha(-1)y(-1). On the Links course, the proportion of trees was much lower (2%) and sequestration from links grassland resulted in a net balance of 0.0 ± 0.2Mg CO(2e) ha(-1)y(-1). Recommendations for golf course management and design include the reduction of nitrogen fertiliser, improved operational efficiency when mowing, the inclusion of appropriate tree-planting and the scaling of component areas to maximise golf course sequestration capacity. The findings are transferrable to the management and design of urban parks and gardens, which range between fairways and greens in intensity of management.

Urban ecological systems: scientific foundations and a decade of progress

Urban ecological studies, including focus on cities, suburbs, and exurbs, while having deep roots in the early to mid 20th century, have burgeoned in the last several decades. We use the state factor approach to highlight the role of important aspects of climate, substrate, organisms, relief, and time in differentiating urban from non-urban areas, and for determining heterogeneity within spatially extensive metropolitan areas. In addition to reviewing key findings relevant to each state factor, we note the emergence of tentative "urban syndromes" concerning soils, streams, wildlife and plants, and homogenization of certain ecosystem functions, such as soil organic carbon dynamics. We note the utility of the ecosystem approach, the human ecosystem framework, and watersheds as integrative tools to tie information about multiple state factors together. The organismal component of urban complexes includes the social organization of the human population, and we review key modes by which human populations within urban areas are differentiated, and how such differentiation affects environmentally relevant actions. Emerging syntheses in land change science and ecological urban design are also summarized. The multifaceted frameworks and the growing urban knowledge base do however identify some pressing research needs.

Soil organic carbon and nitrogen accumulation in plots of rhizoma perennial peanut and bahiagrass grown in elevated carbon dioxide and temperature

Carbon sequestration in soils might mitigate the increase of carbon dioxide (CO2) in the atmosphere. Two contrasting subtropical perennial forage species, bahiagrass (BG; Paspalum notatum Flügge; C4), and rhizoma perennial peanut (PP; Arachis glabrata Benth.; C3 legume), were grown at Gainesville, Florida, in field soil plots in four temperature zones of four temperature-gradient greenhouses, two each at CO2 concentrations of 360 and 700 micromol mol(-1). The site had been cultivated with annual crops for more than 20 yr. Herbage was harvested three to four times each year. Soil samples from the top 20 cm were collected in February 1995, before plant establishment, and in December 2000 at the end of the project. Overall mean soil organic carbon (SOC) gains across 6 yr were 1.396 and 0.746 g kg(-1) in BG and PP, respectively, indicating that BG plots accumulated more SOC than PP. Mean SOC gains in BG plots at 700 and 360 micromol mol(-1) CO2 were 1.450 and 1.343 g kg(-1), respectively (not statistically different). Mean SOC gains in PP plots at 700 and 360 micromol mol(-1) CO2 were 0.949 and 0.544 g kg(-1), respectively, an increase caused by elevated CO2. Relative SON accumulations were similar to SOC increases. Overall mean annual SOC accumulation, pooled for forages and CO2 treatments, was 540 kg ha(-1) yr(-1). Eliminating elevated CO2 effects, overall mean SOC accumulation was 475 kg ha(-1) yr(-1). Conversion from cropland to forages was a greater factor in SOC accumulation than the CO2 fertilization effect.