The role of vegetation in regulating stormwater runoff from green roofs in a winter rainfall climate

Extensive green roofs composed of a thin layer of growing medium topped with vegetation can significantly reduce both the timing and magnitude of stormwater runoff relative to a typical impervious roof. However, regional climatic conditions such as seasonality in rainfall and potential evapotranspiration could strongly alter the stormwater performance of green roofs. In this study we evaluate the stormwater performance of green roofs in the predominately winter rainfall climate of the U.S. Pacific Northwest. We also test whether the amount of irrigation used to maintain green roof vegetation in a seasonally dry climate such as the Pacific Northwest influences stormwater performance. We monitored stormwater performance over one year for sets of experimental roofs constructed using three designs: a conventional impervious design, a medium-only design, and a typical extensive green roof design that included vegetation. During the winter rainy season vegetation had no significant influence on stormwater retention; medium-only and vegetated roofs reduced stormwater runoff nearly identically relative to the impervious roofs. In contrast, during summer vegetated roofs retained significantly more rainfall than medium-only roofs, although this effect depended strongly on the size of the rain event. In addition, total relative retention for both roof types was significantly higher during summer than during winter. Irrigation significantly reduced summer retention capacity of both medium-only and planted roofs, but only during the largest dry season rain event. These results suggest that cool wet season climates such as the Pacific Northwest are challenging ones for green roof stormwater performance. In order to optimize stormwater benefits of green roofs, designers should create explicitly regional designs that include plant selections better matched to the specific environmental and management constraints.     

Vegetation development on extensive vegetated green roofs: Influence of substrate composition, establishment method and species mix

Technology for establishment of vegetated roofs (green roofs) has developed rapidly over recent years but knowledge about how these systems will develop over time is still limited. This study investigates vegetation development on unfertilised thin extensive vegetated roofs during a 3-year period. The vegetation systems investigated were designed to be low maintenance and had a saturated weight of 50 kg/m², a thickness of 4 cm and drought-resistant succulent and bryophyte vegetation.Vegetation development was investigated in relation to: establishment method, species mixture and substrate composition in a factorial experiment. Vegetation cover was investigated using point intercept.Moss was found to develop on most substrates and reached more than 80% cover on some plots. Sedum album and Sedum acre were the dominant species on the roofs. S. acre was found to decrease drastically after 2 years. The lack of difference found in this study between the establishment techniques shows that there are other possible marketable ways to construct vegetated roofs in Sweden, as an alternative to vegetation mats. Uniform extensive vegetated roofs with a high dominance of succulent species have limited value for plant biodiversity, as few species establish spontaneously.     

Effects of Controlled-Release Fertiliser on Nitrogen Use Efficiency in Summer Maize

Nitrogen (N) is a nutrient element necessary for plant growth and development. However, excessive inputs of N will lead to inefficient use and large N losses to the environment, which can adversely affect air and water quality, biodiversity and human health. To examine the effects of controlled-release fertilisers (CRF) on yield, we measured ammonia volatilisation, N use efficiency (NUE) and photosynthetic rate after anthesis in summer maize hybrid cultivar Zhengdan958. Maize was grown using common compound fertiliser (CCF), the same amount of resin-coated controlled release fertiliser (CRFIII), the same amount of sulphur-coated controlled release fertiliser (SCFIII) as CCF, 75% CRF (CRFII) and SCF (SCFII), 50% CRF (CRFI) and SCF (SCFI), and no fertiliser. We found that treatments CRFIII, SCFIII, CRFII and SCFII produced grain yields that were 13.15%, 14.15%, 9.69% and 10.04% higher than CCF. There were no significant differences in grain yield among CRFI, SCFI and CCF. We also found that the ammonia volatilisation rates of CRF were significantly lower than those of CCF. The CRF treatments reduced the emission of ammonia by 51.34% to 91.34% compared to CCF. In addition, after treatment with CRF, maize exhibited a higher net photosynthetic rate than CCF after anthesis. Agronomic NUE and apparent N recovery were higher in the CRF treatment than in the CCF treatment. The N uptake and physiological NUE of the four yield-enhanced CRF treatments were higher than those of CCF. These results suggest that the increase in NUE in the CRF treatments was generally attributable to the higher photosynthetic rate and lower ammonia volatilisation compared to CCF-treated maize.     

Fertiliser Response of soils and vegetation on ultrabasic terraces on the isle of rum between 1965 and 1996

Summary

In 1965, an experiment was begun on the Isle of Rum, in the Inner Hebrides of Scotland. The experiment aimed to determine the limiting effect of soil nutrient deficiency on the re-colonisation of vegetation on the sparsely vegetated slopes of the island's ultrabasic mountain ridges. A fertilisation regime was implemented between 1965 and 1968. In 1996, sampling of a newly established ‘untreated’ plot revealed that, on untreated areas, the soils and vegetation had remained largely unchanged since 1965. Resampling of the fertilised plot however, demonstrated the development of a more organic rich surface soil with a significantly reduced soil acidity and increased soil cation, extractable phosphorus and total nitrogen contents. Most of these changes could be directly attributed to the fertiliser applications. On the fertilised plot, vegetation cover had increased from 5–10% in 1965 to 100% in 1996 and a shift from patchy herb-rich Calluna heath to closed speciesrich Festuca-Agrostis grassland had taken place. A range of acidophile species and bare soil bryophytes had been lost, having been replaced predominantly by grasses and mosses. The importance of nutrient availability as the principal limiting factor on vegetation cover in the study area has been uneqivocally established.     

Effect of organic fertilisers on the greening quality, shoot and root growth, and shoot nutrient and alkaloid contents of turf-type endophytic tall fescue, Festuca arundinacea

Increasing concern about the potential negative environmental impact of chemical fertilisers used in urban landscapes has provided impetus to develop organic fertilisers. However, little is known about the effect of organic fertilisers on turfgrass quality, growth and stress resistance. This study compared the effect of 11 organic fertilisers, applied at manufacturer's recommended rates, on greening quality, shoot and root growth, and shoot nutrient (an indication of nutrient uptake) and alkaloid content (an indication of insect resistance) in endophytic (infected with the fungus Neotyphodium coenophialum) tall fescue in the greenhouse. We measured turfgrass greening quality on a 1–9 scale weekly (9 being the highest), shoot and root growth monthly, and shoot contents of macro- and micronutrients and of various alkaloids at the end of 4 months. The results show that Corn Gluten and Cockadoodle Doo produce the highest turfgrass greening quality and shoot growth. Nature's Touch with enzymes enhanced root growth, and thus resulted in high root:shoot ratio, especially in third and fourth months after application. Compared with the most commonly used chemical fertiliser, Scott's Turf Builder, the organic fertilisers Cockadoodle Doo, Corn Gluten and Nature's Touch with enzymes generally resulted in better turf greening quality. Although Cockadoodle Doo, Vigoro and Scott's Turf Builder resulted in higher macronutrient contents in turfgrass shoots, there was no significant correlation between the nutrient contents in the fertilisers and in the shoots four months after application. Significant differences were found for all measured alkaloids in turfgrass shoots among the 13 treatments, and these differences varied with fertiliser. Overall, organic fertilisers produced higher turfgrass greening quality, root and shoot growth and insect resistance capacity (alkaloid content) compared with the chemical fertiliser, Scott's Turf Builder. On the basis of the high to excellent turfgrass greening quality ratings, root:shoot ratio, shoot nutrient and alkaloid contents in this study, we conclude that Cockadoodle Doo, Vigoro and Nature's Touch with enzymes are relatively superior organic fertilisers.     

Runoff water quality from intensive and extensive vegetated roofs

Vegetated roofs are becoming a trend in urban design, among others as a tool for city greening, mitigating urban heat island effect, and lowering urban storm runoff. Additionally, pollutant removal within vegetated roofs is often expected; however, it is commonly not a design feature. This study investigated influence on runoff water quality from two full-scale vegetated roofs (an intensive from Japan and an extensive from Sweden). Results show that both extensive and intensive vegetated roofs are a sink of nitrate nitrogen and ammonium nitrogen with similar performance. The intensive vegetated roof is also a sink of total nitrogen in contrast to the extensive roof. Phosphorus release is observed from the extensive vegetated roof but not from the intensive vegetated roof; release of dissolved organic carbon and potassium is observed from both roofs. The vegetated roofs, if not retaining the metal pollutants, were generally not a significant source. The increase of average pH during rainwater passage through the intensive vegetated roof indicated rapid neutralization of the acid depositions.     

Quantitative proteomics to study the response of potato to contrasting fertilisation regimes

There is concern over the sustainability and environmental impact of mineral fertilisers and crop protection inputs used in intensive arable crop production systems. However, replacing mineral with organic fertilisers (animal and green manures) and restricting the use of chemosynthetic crop protection may significantly reduce crop yields. The effects of (a) replacing mineral with composted cattle manure fertiliser input and (b) omitting pesticide-based crop protection on potato (Solanum tuberosum) tuber yield, leaf and tuber mineral nutrient content and leaf protein profiles were investigated. Switching to organic fertiliser had a greater effect on yield and protein profiles than the omission of chemosynthetic crop protection. Leaf N and P composition were significant drivers of protein expression, particularly proteins involved in photosynthesis such as the large subunit of RuBisCO, RuBisCO activase and the photosystem I reaction centre, which were at higher abundances in potato leaves grown under mineral fertiliser regimes. Proteins known to be induced in response to stress, such as dehydroascorbate reductase and Glutathione S-transferases, were also shown to be up-regulated under mineral fertilisation, possibly associated with higher Cd composition, whereas two proteins known to be involved in biotic stress (1,3-β-d-glucan glucanohydrolase; putative Kunitz-type tuber invertase inhibitor) were more abundant under compost fertilisation. Results showed that switching from mineral to organic fertilisers led to reduced N availability, a significant change in leaf protein expression and lower tuber yield. In contrast, omission of chemosynthetic crop protection inputs had limited effects on protein expression and no significant effect on tuber yield. This study provides information on the effects of changes in nutrient supply on protein expression patterns. It is a prerequisite for the development of functional molecular markers for a directed strategy to inform breeding programmes to improve potato nutrient use efficiency.     

Changes in nutrient use efficiency, status and retranslocation in young post-fire regeneration Pinus halepensis in response to sudden N and P input, irrigation and removal of competing vegetation

The capacity of Mediterranean species to adapt to variable nutrient supply levels in a global change context can be a key factor to predict their future capacity to compete and survive in this new scenario. We aimed to investigate the capacity of a typical Mediterranean tree species, Pinus halepensis, to respond to sudden changes in N and P supply in different environmental conditions. We conducted a fertilisation, irrigation and removal of competing vegetation experiment in a calcareous post-fire shrubland with an homogeneous young (5 years old) population of P. halepensis in order to investigate the retranslocation and nutrient status for the principal nutrients (N, P, Mg, K, S, Ca and Fe), and the nutrient use efficiency (NUE) of the most important nutrients linked to photosynthetic capacity (N, P, Mg and K). P fertilisation increased P concentration in needles, P, N, Mg and K retranslocations, and NUE calculated as biomass production per unit of nutrient lost in the litterfall. The P fertilisation was able to increase the aboveground biomasses and P concentration 3 years after P fertiliser application. Those responses to P fertilisation were enhanced by the removal of competing vegetation. The N needle and litterfall concentration decreased after P fertilisation and this effect was greater when the P fertilisation was accompanied by removal of competing vegetation. The increase of P availability decreased the P-NUE and increased the N-NUE when these variables were calculated as aboveground biomass production per unit of P present in the biomass. Both P-NUE and N-NUE increased when calculated as total aboveground production per unit of nutrient loss. The results show that it is necessary to calculate NUE on a different basis to have a wider understanding of nutrient use. The irrigation did not change the needle nutrient concentrations and the litterfall production, but it significantly changed the nutrient litterfall concentrations and total aboveground contents (especially P and K). These results show a high capacity of P. halepensis to quickly respond to a limiting nutrient such as P in the critical phases of post-fire regeneration. The increase in P availability had a positive effect on growth and P concentrations and contents in aboveground biomass, thus increasing the capacity of growth in future periods and avoiding immediate runoff losses and leachate. This capacity also strongly depends on neighbour competition.     

Towards soil management with Zn and Mn: estimates of fertilisation efficacy of Citrus trees

Nutrient management recommendations for fruit crops lack the understanding of the efficiency of soil fertilisation with manganese (Mn) and zinc (Zn), which could substitute, in part, the traditional foliar applications. Fruit yield of trees in response to Zn and Mn supply via soil may be limited either by sorption reactions with soil colloids or low solubility of fertilisers. We investigated the effects of fertiliser sources and rates of Mn and Zn applied to soils with different sorption capacities on nutrient uptake, biochemical responses and biomass of Citrus. Two experiments were carried out with 2‐year‐old sweet orange trees that received applications of Mn or Zn. The first experiment evaluated the application of Mn fertilisers (MnCO₃ and MnSO₄) at three levels of the nutrient (0, 0.7 and 3.5 g plant^?1 of Mn) in two types of soil (18.1% and 64.4% of clay, referred to as sandy loam and clay soils, respectively). The second experiment, likewise, evaluated Zn fertilisers (ZnO and ZnSO₄) and nutrient levels (0, 1.0 and 5.0 g plant^?1 of Zn). Application of Mn and Zn increased nutrient availability in the soils as well as leaf nutrient concentrations in the trees. The lowest rates, 0.7 g plant^?1 of Mn and 1.0 g plant^?1 of Zn, both as sulphate, were sufficient to supply these micronutrients to sufficient levels in leaves, flowers and fruits. Metal toxicity to plants occurred with higher doses of both nutrients and to a large extent in the sandy soil. In this case, protein bands lower than 25 kDa were observed as well a decrease on leaf chlorophyll content. In the clay soil, despite increased micronutrient concentrations in the plant, responses were less pronounced because of higher adsorption of metals in the soil. Superoxide dismutase (SOD, EC 1.15.1.1) isoenzyme activity was determined by non‐denaturing polyacrylamide gel electrophoresis (PAGE). The Cu/Zn‐SOD isoenzymes increased with increased Zn rates, but in contrast, when Mn was applied at the highest rate, the activity of Cu/Zn‐SODs decreased. The SOD activity pattern observed indicated increased production of superoxide and consequently an oxidative stress condition at the highest rates of Zn and Mn applied. The results demonstrated that the soil application of Mn and Zn can supply nutrient demands of orange trees, however the low solubility of fertilisers and the high sorption capacity of soils limit fertilisation efficiency. On the contrary, application of sulphate source in sandy soils may cause excess uptake of Mn and Zn and oxidative stress, which impairs the photosynthetic apparatus and consequently tree growth.     

Green roof performance towards management of runoff water quantity and quality: A review

This review paper addresses the role of green roofs in urban drainage considering both management of water quantity and quality. Results from investigation of full scale installations as well as from laboratory models are reviewed. The following factors affecting runoff dynamics from green roofs are discussed: type of green roof and its geometrical properties (slope); soil moisture characteristics; season, weather and rainfall characteristics; age of green roof; vegetation. Design parameters as suggested by different authors are also reviewed. Factors which affect influence of a green roof on runoff water quality are discussed in general terms followed by the review of data regarding concentrations of phosphorus, nitrogen, and heavy metals in green roof runoff, its’ pH, and first flush effect. Linking among fertilization, runoff pollution and vegetation development is given a particular focus. The review indicates clearly that there is a need for more research into a green roof performance in an urban environment. The differences measured by few existing studies between the early years performance of green roofs and the later years indicate a need for long term monitoring of green roofs.     

Uptake of zinc and phosphorus by plants is affected by zinc fertiliser material and arbuscular mycorrhizas

Background and Aims

Water solubility of zinc (Zn) fertilisers affects their plant availability. Further, simultaneous application of Zn and phosphorus (P) fertiliser can have antagonistic effects on plant Zn uptake. Arbuscular mycorrhizas (AM) can improve plant Zn and P uptake. We conducted a glasshouse experiment to test the effect of different Zn fertiliser materials, in conjunction with P fertiliser application, and colonisation by AM, on plant nutrition and biomass.

Methods

We grew a mycorrhiza-defective tomato genotype (rmc) and its mycorrhizal wild-type progenitor (76R) in soil with six different Zn fertilisers ranging in water solubility (Zn sulphate, Zn oxide, Zn oxide (nano), Zn phosphate, Zn carbonate, Zn phosphate carbonate), and supplemental P. We measured plant biomass, Zn and P contents, mycorrhizal colonisation and water use efficiency.

Results

Whereas water solubility of the Zn fertilisers was not correlated with plant biomass or Zn uptake, plant Zn and P contents differed among Zn fertiliser treatments. Plant Zn and P uptake was enhanced when supplied as Zn phosphate carbonate. Mycorrhizal plants took up more P than non-mycorrhizal plants; the reverse was true for Zn.

Conclusions

Zinc fertiliser composition and AM have a profound effect on plant Zn and P uptake.     

Simulated and measured nitrogen conditions in a manured and fertilised soil

The governing factors for soil nitrogen dynamics were identified with a simulation model. In addition, the model was used to interpret measurements from a plot fertilisation experiment in southwest Sweden.Simulated moisture and temperature conditions were the driving variables for the simulation of soil nitrogen dynamics and leaching during a 6-year period. The results of the simulation were compared with monthly observations on two plots with grain crops, one with liquid manure and commercial fertilisers applied and one with commercial fertilisers only.Simulated temporal variations of the nitrate and ammonium storages generally agreed with observations. The dominant role of the crops as a determinant of soil nitrogen conditions was demonstrated. A higher leaching loss from the plot with application of commerical fertilisers only occurred both in simulations and measurements compared to the plot with application of both commercial fertilisers and manure. The main reason was the higher N-application in the former treatment.The effect of water flows in macropores was interpreted as a delay of simulated leaching compared to observed leaching on some occasions in summer and early autumn. No direct effect of the macropores on the yearly rates of leaching could be seen.     

Effects of a compost made from the solid by-product ("alperujo") of the two-phase centrifugation system for olive oil extraction and cotton gin waste on growth and nutrient content of ryegrass (Lolium perenne L.)

A pot experiment was conducted on a low-fertility calcareous soil in order to evaluate the effect on ryegrass growth and nutrient uptake of an organic fertiliser obtained by composting "alperujo" and cotton gin waste. Compost, alone and combined with nitrogen fertilisation, was added to the soil at three rates and three harvests were obtained. The compost application enhanced plant growth in the first and third harvest. However, the additional nitrogen fertilisation clearly improved soil productivity due to the scarce availability of this nutrient in the compost. Also, a general increase in the plant contents of phosphorus and potassium in the first two harvests was recorded, whereas treatments with the maximum compost rate showed the highest plant content of copper in the last two harvests. Decreases in calcium in the last two harvests, in magnesium in all of them and in iron and manganese in the last harvest were also observed.     

The effect of time of fertiliser-soil contact,distance of phosphate movement and fertiliser solubility on phosphate availability to early growth of lowland rice

Summary The importance of time of fertiliser-soil contact, distance of phosphate movement from fertiliser and phosphate fertiliser solubility in determining the availability of phosphate to the early growth of lowland rice was investigated. Phosphate availability was measured by phosphate uptake in a glass-house experiment in which two week old rice seedlings were transferred to the surface of fertiliser-treated soils for three weeks before harvesting. The fertilisers used in the study were monoammonium phosphate (MAP), ammonium polyphospate (APP), superphosphate (SP) and rock phosphate (RP). Availability of all fertilisers was tested in this way after 2, 4 and 8 weeks of fertiliser-soil contact. In an associated laboratory experiment the distance of phosphate movement and fertiliser solubility (as measured by quantity of phosphate that had moved away from the fertilizer source) was determined at 2 and 4 weeks in glass tubes containing waterlogged soil. The results showed that at all times of measurement, the availability of the fertilisers could be ranked MAP>APP≥SP>RP. Of the 6 possible correlations between phosphate uptake and phosphate movement, only one was significant for the fertiliser-soil contact period of 2 weeks and phosphate movement at 4 weeks, (r=0.950, P<0.05). Of the 6 possible correlations between phosphate uptake and fertiliser solubility, none were significant. However, of the 6 possible correlations between phosphate uptake and the product of the two laboratory parameters (referred to as the availability index) four were significant (P<0.05 in all cases), and involved only the fertiliser-soil contact periods of 2 and 4 weeks. These results indicate that fertiliser solubility alone is not a satisfactory correlative determinant of availability of fertiliser phosphate to lowland rice. Phosphate movement alone is marginally better, but the best correlations are obtained when both parameters are taken into account. While their combined effects are evident only during the first four weeks after fertiliser application, this may still be important to the successful establishement of a rice crop.     

Improving fertiliser efficiency on calcareous and alkaline soils with fluid sources of P,N and Zn

Alkaline calcareous or sodic soils represent an important proportion of the world's arable soils and are important for cereal production. For calcareous soils in general, despite high applications of P fertiliser for many years, P deficiency in cereals is common. Field experiments were conducted to test the relative ability of granular (e.g. DAP, MAP and TSP) and fluid fertilisers to supply P to wheat on grey calcareous and red brown calcareous sandy loam soils (Calcixerollic xerochrepts). A pot experiment was also conducted with these soils and with two non-calcareous alkaline soils to investigate the effects of placement on the efficiency of fertiliser performance. In 1998, fluid and granular sources of P, N and Zn were compared in the field by banding below the seed at sowing. In 1999, MAP applied as granular, and technical grade MAP applied as fluid, were compared as sources of P in rate response experiments. First year results showed that fluid sources of P, N and Zn produced significantly more grain than the granular product. In the following year, fluid fertilisers were found to produce significantly higher response curves for shoot dry weight, grain yield and P uptake in grain. At a commercial rate of 8 kg P ha^–1, fluid fertiliser produced between 22% and 27% more grain than the granular product. Soil moisture and fertiliser placement effects are implicated in the higher efficiency of fluid fertilisers.     

The effect of catch crop species on selenium availability for succeeding crops

Background and Aims

Selenium (Se) is an essential nutrient for humans and animals. In order to ensure an optimal concentration of Se in crops, Se fertilisers are applied. Catch crops may be an alternative way to increase Se concentrations in vegetables.

Methods

Three experiments in Denmark between 2007–10 investigated the ability of catch crops (Italian ryegrass, fodder radish and hairy vetch) under different fertiliser regimes to reduce soil Se content in the autumn and to increase its availability in spring to the succeeding crop.

Results and Conclusions

The catch crops (Italian ryegrass and fodder radish) increased water-extractable Se content in the 0.25–0.75?m soil layer in only one of the experiments. Selenium uptake by the catch crops varied between 65 and 3263?mg?ha^?1, depending on species, year and fertilisation treatment; this corresponded to 0.1–3.0% of the water-extractable soil Se content. The influence of catch crops on Se concentrations and uptake in onions and cabbage was low. There was a decrease in Se uptake and recovery of applied Se by onions following catch crops, which might indicate Se immobilisation during catch crop decomposition.     

Nitrogen uptake in a Norway spruce stand following ammonium sulphate application,fertigation, irrigation,drought and nitrogen-free-fertilisation

The above-ground accumulation of N,N uptake and litter quality resulting from improved or deteriorated availability of water and nutrients in a 25 year old Norway spruce stand in SW Sweden (as part of the Skogaby project) is presented. Treatment include irrigation; artificial drought; ammonium sulphate addition; N-free-fertilisation and irrigation with liquid fertilisers including a complete set of nutrients according to the Ingested principle (fertigation). At start of the experiment the stand contained 86.5 t dry mass and 352 kg N ha⁻¹. The following three years the annual N uptake in untreated trees was 32 kg N ha⁻¹ to be compared with the annual N throughfall of 17 kg ha⁻¹. Simultaneously, the treatment with ammonium sulphate and liquid fertilisation resulted in 48 and 56 kg ha⁻¹ y⁻¹, respectively, in treatment specific N-uptake following an application of 100 kg N ha⁻¹ y⁻¹. Addition of a N-free fertiliser resulted in improved N-uptake by 19 kg N ha⁻¹ y⁻¹ and irrigation by 10 kg N ha⁻¹ y⁻¹, compared to control. A linear relation between total above-ground dry mass production and N-uptake was found for trees growing with similar water availability. Dry mass production increased with increased water availability given the same N-uptake. It is concluded that the studied stand this far is not N saturated', as N fertilisation resulted in both increased N uptake and increased growth. Addition of a N-free-fertiliser resulted in increased uptake of N compared to the control, indicating an increased mineralisation rate or uptake capacity of the root system. The linear relation between N uptake and biomass production shows that at this study site N is a highly limiting factor for growth.     

Hydrological performance of extensive green roofs in response to different rain events in a subtropical monsoon climate

Rapid urbanization transforms permeable land into developed areas with predominantly impervious surfaces, significantly increasing stormwater runoff and exacerbating the risk of pluvial flooding. Green roofs provide an attractive strategy for increasing surface permeability by mimicking pre-development hydrologic functions and mitigating flood risks in compact cities. However, the potential of this strategy has not been rigorously assessed, despite advances in global stormwater management. This is mainly due to insufficient scientific knowledge of hydrologic performance and a lack of experimental studies of rainwater-harvesting capacity under specific climatic conditions. This study evaluated the hydrologic performance of a real-scale extensive green roof (EGR) constructed in a subtropical monsoon climate in Nanjing, China. Overall, the EGR showed considerable ability to retain rainfall (mean retention ~?60%, accumulated retention ~?30%), although retention performance varied from 11% to 100% depending on the rainfall event considered, and decreased with increasing rainfall. Event-based rainfall–runoff comparisons demonstrated that the EGR retained rainwater efficiently during the early stages of a rainfall event and significantly attenuated peak runoff flows compared to bare roofs. Statistical analysis showed that total rainfall depth, rainfall duration, and substrate layer moisture influenced the overall retention most strongly, but also the percentage retention and runoff depth, highlighting the impact of substrate properties in addition to rainfall characteristics on EGR hydrologic performance. These findings provide new knowledge of and important insights into the hydrological performance of green roofs in subtropical monsoon climates, which could be used to guide EGR construction to increase landscape permeability, mitigate the risk of pluvial flooding, and enhance the climatic resilience of urban regions.

     

Turfgrass (Cynodon dactylon L.) sod production on sandy soils: I. Effects of irrigation and fertiliser regimes on growth and quality

The effects on growth, quality and N uptake by turfgrass (Cynodon dactylon L.) during sod production of four fertiliser types applied at three application rates (100, 200 or 300 kg N ha⁻¹ per ‘crop’) under two irrigation treatments (70% and 140% daily replacement of pan evaporation) were investigated. The fertiliser types were: water-soluble (predominately NH₄NO₃), control-release, pelletised poultry manure, and pelletised biosolids; and the experiment was conducted on a sandy soil in a Mediterranean-type climate. Plots were established from rhizomes, with the turfgrass harvested as sod every 16–28 weeks depending upon the time of the year. Four crops were produced during the study. Applying water-soluble and control-release fertilisers doubled shoot growth and improved turfgrass greenness by up to 10% in comparison with plots receiving pelletised poultry manure and pelletised biosolids. Nitrogen uptake into the shoots after four crops (averaged across irrigation treatments and N rates) was 497 kg N ha⁻¹ for the water-soluble fertiliser, 402 kg N ha⁻¹ for the control-release, 188 kg N ha⁻¹ for the pelletised poultry manure and 237 kg N ha⁻¹ for the pelletised biosolids. Consequently, the agronomic nitrogen-use efficiency (NAE, kg DM kg⁻¹ N applied) of the inorganic fertilisers was approximately twice that of the organic fertilisers. Increasing irrigation from 70% to 140% replacement of pan evaporation was detrimental to turfgrass growth and N uptake for the first crop when supplied with the water-soluble fertiliser. Under the low irrigation treatment, inorganic N fertilisers applied at 200–300 kg N ha⁻¹ were adequate for production of turfgrass sod. Section Editor: P. J. Randall     

Laboratory study of heavy metal phytoremediation by three wetland macrophytes

Detention ponds and constructed wetlands have proven to be effective in reducing peak stormwater runoff volume and flow, and recent interest has extended to utilizing them to improve stormwater runoff quality. A review of stormwater runoff studies indicated that lead, zinc, copper, cadmium, phosphorus, and chloride are contaminants of primary concern. In laboratory settings, the uptake of contaminants by three wetland plant species, Glyceria grandis, Scirpus validus, and Spartina pectinata, was examined and removal rates from nutrient solutions inflow and nonflow reactors were measured. The removal rates varied by plant species and target contaminant, and no one species was the best accumulator of all six contaminants. Belowground tissues of all three species accumulated higher concentrations of the four heavy metals and aboveground tissues accumulated higher concentrations of phosphorus and chloride. Plants grown in flow reactors showed significantly higher accumulation rates than those grown in nonflow reactors. Also, plants grown hydroponically accumulated higher concentrations of the six target contaminants than those grown in sand reactors. However, those grown in sand had a much greater increase of biomass and removed a greater mass of the six target contaminants. Removal rates measured in these experiments can be used to design detention ponds to maximize stormwater remediation.