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Nikolaos Ntoulas, Panayiotis A. Nektarios, and Glykeria Gogoula

A field study evaluated composted olive mill waste (OMC) as a soil amendment in Cynodon dactylon (bermudagrass; C4) turf establishment and maintenance. The study comprised two substudies, each of which had discrete goals: 1) an evaluation of OMC effects on overall bermudagrass growth over the course of 2.5 years when established by seed and subsequently from sprouting of existing rhizomes (2002 to 2004); and 2) a re-evaluation of OMC effects on bermudagrass establishment by seed (2003). Twenty-four plots (1.44 × 1.44 m) were filled with sandy-loam soil and supplemented with one of three OMC proportions (low= 12.5%, medium = 25%, and high = 50% by volume, indicated as substrates S:OMCL, S:OMCM, and S:OMCH, respectively), and non-amended soil served as a control (S). The study evaluated: 1) the substrate's chemical and physical characteristics, including bulk density, water retention curves, pH, and electrical conductivity (EC) measurements; 2) the establishment rate of C. dactylon, either by seed or by sprouting of existing rhizomes after dormancy as determined by measurements that included vertical detachment force (VDF), root growth, and substrate moisture; and 3) the growth rate of C. dactylon as determined through measurements of visual quality, clipping dry weight, root growth, and VDF. The results show that OMC decreased substrate pH in proportion to the OMC supplementation rate and increased EC only at the end of the study and only in the plots with the highest supplementation rate (S:OMCH). Water retention was improved by OMC incorporation except from S:OMCL, which increased water retention only at low tensions. Compared with soil alone, bulk density decreased by 13.5%, 19.7%, and 32.8% as the OMC rate increased, respectively, from 12.5% to 50%. The OMC rate of 50% v/v resulted in a minor reduction in plant visual quality during the cold periods but in a slight improvement during the warm periods. The clipping dry weights were increased by OMC amendments in 2003, which was considered a disadvantage because of the insignificant visual quality differences between substrates during the 2 study years. In 2004, the clipping yields were unaffected by OMC rate. Root dry weight response to OMC varied. For the highest OMC rate, root dry weight was lower during the cold and wet periods, greater during the first stages of bermudagrass establishment by seed, and similar compared with soil without OMC during turf establishment from the sprouting of existing rhizomes after dormancy. The highest OMC rate reduced resistance to vertical detachment force at four sampling dates (of six) during the 2002–2003 study, because the reduced root dry weight and/or increased moisture of the substrate facilitated bermudagrass detachment. In contrast, OMC-supplemented substrates resulted in increased VDF at the first sampling date of establishment both by seed (2003) and by rhizome sprouting after dormancy (2004). It was concluded that, when speedy establishment is imperative (such as in sod farms) or when irrigation is limited, an OMC rate of 50% by volume should be selected. In contrast, for sustainable bermudagrass growth, a rate of 12.5% by volume is preferred, because it increases the visual quality of the grass and root growth.

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Nikolaos Ntoulas, Panayiotis A. Nektarios, and Efthimia Nydrioti

The use of turfgrasses might provide an additional solution for establishing green roofs in urban environments. The aim of the present study was to determine Manilagrass [Zoysia matrella (L.) Merr. ‘Zeon’] drought tolerance when grown under green roof conditions and under two different irrigation regimes. Treatments included: 1) two extensive green roof substrates {locally produced substrate [3 sandy loam soil:8 pumice:4 perlite:4 compost:1 zeolite (by volume)] and a commercially available substrate based on crushed tiles}; 2) two substrate depths (7.5 cm or 15 cm); and 3) two irrigation regimes (3 mm or 6 mm of irrigation every 3 days). Substrate characteristics (particle size distribution, saturated and dry bulk density, total porosity, water potential curves, in situ substrate moisture, pH, electrical conductivity, and nutrient analysis), turfgrass growth, and physiological status [green turf cover (GTC), normalized difference vegetation index (NDVI), and leaf relative water content (RWC)] were determined. During moisture deficit periods, GTC, NDVI, and RWC were most affected by substrate depth; moderately affected by irrigation regime; and, to a lesser extent, by substrate type. Turfgrass growth and physiological status were best during moisture deficit conditions in the deeper profile (15 cm) using the higher amount of irrigation (6 mm) and the locally mixed substrate.

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George Kargas, Nikolaos Ntoulas, and Panayiotis A. Nektarios

Little is known about the accuracy of soil moisture dielectric sensors in coarse-textured root zones and green roof substrates. In the present study, the accuracy of two dielectric sensors of different technologies (frequency domain and time domain dielectric sensor) in measuring moisture content was investigated in six coarse-textured green roof substrates. Calibration equations were developed for both sensors, and the effect of electrical conductivity (EC) on substrate moisture content calculation was determined. It was found that for frequency domain sensor the relationship between dielectric permittivity square root () and actual substrate moisture content (θ m) was strongly linear for all tested substrates. However, for each substrate a distinct specific calibration equation of was required. The correlation between substrate permittivity and EC was linear for frequency domain sensor for all moisture levels (0% to 35%). In the case of time domain sensor, each green roof substrate was also described from a different calibration curve between actual substrate moisture content and period of time that was recorded by the device. It was found that their relationship was quadratic for all substrates. In addition, time domain sensor output responded in a quadratic manner to increasing levels of EC. This response was found to interact with actual substrate moisture content as well. It was concluded that the most reliable results for moisture content determination of the coarse-textured green roof substrates were obtained by substrate-specific calibration curves for both dielectric sensors.

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Panayiotis A. Nektarios, Ioannis Amountzias, Iro Kokkinou, and Nikolaos Ntoulas

Extensive green roofs are a promising technology for reintroducing lost flora in degraded urban environments, but further research is needed for their application in semiarid regions. Therefore, research was undertaken to determine the effects of substrate type and depth and the amount of irrigation during a drought period on the establishment, growth, and physiology of the native species Dianthus fruticosus sub. fruticosus. Treatments included two substrate types [a soilless substrate (Pum50:Per20:C20:Z10) or a substrate with soil (S15:Pum40:Per20:C20:Z5), in which Pum = pumice; Per = perlite; C = compost; Z = clinoptinolite zeolite; and S = sandy loam soil, mixed in a volumetric proportion indicated by their subscripts], two substrate depths (7.5 cm or 15.0 cm), and two irrigation regimens during drought [15% or 30% of pan evaporation (Epan)]. Measurements included substrate characteristics such as particle size distribution, dry and saturated bulk density, water characteristic curves, and in situ determination of substrate moisture during drought stress. Plant growth was determined based on biometric measurements such as growth index (GI) and dry weight and physiological indicators such as SPAD, chlorophylla+b, and carotenoid contents. It was found that substrate moisture during drought was increased in the soil substrate compared with the soilless substrate as a result of its better water retention capacity in low tensions. Dianthus fruticosus sub. fruticosus growth was promoted by the deep substrate (15 cm) throughout the entire study, whereas substrate type and irrigation during the drought period did not have an effect. Similarly, leaf dry weight was increased in the deeper substrates, whereas shoot and root dry weights were similar in all treatments. SPAD was found to be a more sensitive method than chlorophyll and carotenoid analysis and revealed an interesting sequence of treatment influences on D. fruticosus sub. fruticosus physiology that depended on the climatic conditions and stress imposition. More specifically, during establishment, both substrate type and depth affected growth with the soil substrate and deep profiles yielding higher SPAD measurements. Soon after the initiation of drought, the deep profiles had higher SPAD values than the shallow ones, whereas in high-irrigation regimens and, to a less extent, deeper profiles provided increased SPAD values after the middle of drought imposition. Chlorophyll and carotenoid levels reduced during the drought stress period, but very limited differences were detected between treatments. It was concluded that D. fruticosus sub. fruticosus is a very promising native plant for use on extensive green roofs in the Mediterranean region, and its growth was better in a substrate depth of 15 cm. However, its growth was sufficient even with a 7.5-cm substrate depth and irrigation of 15% Epan.

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Panayiotis A. Nektarios, Serafim Kastritsis, Nikolaos Ntoulas, and Panayiota Tsiotsiopoulou

Ten substrates were evaluated for their capacity to promote the growth of potted Lantana camara. The substrates consisted of different volumetric proportions of sandy loam soil (S), peat (P), perlite (Per), and urea formaldehyde resin foam (UFRF referred to as F), the latter in an effort to substitute peat use in horticulture. The substrates studied were: S, S60:P40, S40:P60, S60:F40, S40:F60, P60:F40, P40:F60, S40:P30:Per30, S40:F30:Per30, and P50:Per50. Measurements included: 1) substrate physical and chemical characteristics such as water characteristic curves, bulk density, total porosity, easily available water, and pH; 2) biometric measurements such as shoot length and number and number of flowers; and 3) determination of main and lateral stems, leaf, flower, and root dry weights. Results showed that substrates P60:F40 and P40:F60 retained excessive water in all tensions, whereas substrate P50:Per50 exhibited increased water retention at saturation that was quickly reduced after 10 cm of tension. The non-amended soil (S) had the least water retention capacity and proved to be a slow-draining substrate. Supplementation either with peat or peat and perlite (S60:P40, S40:P60, and S40:P30:Per30) significantly increased water retention in the soil-based substrates. Soil-based substrates supplemented with UFRF retained less water compared with peat-amended soil-based substrates. Concerning plant growth, Lantana plants growing in the UFRF-amended substrates were unable to recover from frost injury and their evaluation was interrupted after winter as a result of total plant loss. The injury was attributed to the reduction of plant growth in UFRF-supplemented substrates before the occurrence of frost stress events. Soil-based substrates (S, S60:P40, S40:P60, and S40:P30:Per30) provided greater shoot growth, which was almost twofold compared with substrate P50:Per50. Substrate S40:P30:Per30 produced the most lateral shoots and flowers over the whole study period, whereas S40:P60 produced the most flowers during the summer. Dry weights of both stem and lateral stems followed a similar pattern with the biometric measurements. However the non-amended soil (S) produced the highest leaf and root dry weights followed by substrates S60:P40 and S40:P60. It was concluded that both substrates S40:P60 and S40:P30:Per30 can successfully be used for Lantana nursery production as a result of their decreased bulk density, increased water retention capacity, adequate porosity, and promotion of shoot growth and flowering. Despite its high bulk density, substrate S could be used in the production of Lantana plants for landscape use as a result of the increased root production.

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Iro Kokkinou, Nikolaos Ntoulas, Panayiotis A. Nektarios, and Dimitra Varela

The aim of this study was to determine the effects of different irrigation regimens on five native aromatic and medicinal species including Ballota acetabulosa (Greek horehound), Helichrysum orientale (helichrysum), Melissa officinalis (lemon balm), Rosmarinus officinalis (rosemary), and Salvia fruticosa (Greek sage) when grown on adaptive green roof systems. The applied levels of irrigation were 100% (well-watered control), 75%, 50%, 25%, and 0% (no irrigation) of the daily pan evaporation (Epan). Measurements included the in situ determination of substrate moisture, stomatal resistance, and soil plant analysis development (SPAD) values. It was found that Greek horehound, helichrysum, and rosemary can sustainably grow at an irrigation of 25% Epan, whereas Greek sage and lemon balm require an irrigation of at least 50% Epan for sustainable growth in shallow adaptive green roof systems.

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Nikolaos Ntoulas, Panayiotis A. Nektarios, Thomais-Evelina Kapsali, Maria-Pinelopi Kaltsidi, Liebao Han, and Shuxia Yin

Several locally available materials were tested to create an optimized growth substrate for arid and semiarid Mediterranean extensive green roofs. The study involved a four-step screening procedure. At the first step, 10 different materials were tested including pumice (Pum), crushed tiles grade 1–2 mm (T1–2), 2–4 mm (T2–4), 5–8 mm (T5–8), 5–16 mm (T5–16), and 4–22 mm (T4–22); crushed bricks of either 2–4 mm (B2–4) or 2–8 mm (B2–8); a thermally treated clay (TC); and zeolite (Zeo). All materials were tested for their particle size distribution, pH, and electrical conductivity (EC). The results were compared for compliance with existing guidelines for extensive green roof construction. From the first step, the most promising materials were shown to include Pum, Zeo, T5–8, T5–16, and TC, which were then used at the second stage to develop mixtures between them. Tests at the second stage included particle size distribution and moisture potential curves. Pumice mixed with TC provided the best compliance with existing guidelines in relation to particle size distribution, and it significantly increased moisture content compared with the mixes of Pum with T5–8 and T5–16. As a result, from the second screening step, the best performing substrate was Pum mixed with TC and Zeo. The third stage involved the selection of the most appropriate organic amendment of the growing substrate. Three composts having different composition and sphagnum peat were analyzed for their chemical and physical characteristics. The composts were a) garden waste compost (GWC), b) olive (Olea europaea L.) mill waste compost (OMWC), and c) grape (Vitis vinifera L.) marc compost (GMC). It was found that the peat-amended substrate retained increased moisture content compared with the compost-amended substrates. The fourth and final stage involved the evaluation of the environmental impact of the final mix with the four different organic amendments based on their first flush nitrate nitrogen (NO3 -N) leaching potential. It was found that GWC and OMWC exhibited increased NO3 -N leaching that initially reached 160 and 92 mg·L−1 of NO3 -N for OMWC and GWC, respectively. By contrast, peat and GMC exhibited minimal NO3 -N leaching that was slightly above the maximum contaminant level of 10 mg·L−1 of NO3 -N (17.3 and 14.6 mg·L−1 of NO3 N for peat and GMC, respectively). The latter was very brief and lasted only for the first 100 and 50 mL of effluent volume for peat and GMC, respectively.