Superabsorbent hydrogels are a particular class of gels, obtained by chemical stabilization of hydrophilic polymers in a tridimensional network. Hydrogels have been widely proposed over the last 40 years for agricultural use with the aim to ameliorate water availability for plants, by increasing water holding properties of growing media (soils or soilless substrates). Most of the traditional hydrogels on the market are acrylate-based products, thus not biodegradable. Due to the increasing attention for environmental protection issues, biodegradable hydrogels arise lively interest for potential commercial application in agriculture. In this study, we evaluated a novel class of cellulose-based superabsorbent hydrogels, totally biodegradable and biocompatible, for agricultural use. The objectives of the tests carried out were: 1) to verify the ability of the hydrogel to modify the water retention properties of the growing media (soils and soilless substrates); 2) to study the effects on the growth of plants grown on media amended with the hydrogel. Water retention curve of a sandy soil amended with 0, 0.5, 1.0 and 2.0% (w/w) of hydrogel was determined using a Richard's pressure plate apparatus. The hydrogel modified the soil water retention properties. The soil moisture at field capacity increased with the highest hydrogel percentage up to 400% compared to the not amended soil, and at wilting point (-15 bar) was similar to that at field capacity of the not amended soil. When added to perlite, a low water holding capacity soilless substrate, 1 or 2% (w/w) of hydrogel increased the container capacity of 28 and 48%, respectively, with no decrease of air capacity. Tests revealed absence of phytotoxicity of the hydrogel, and cultivation trials on cucumber (on soil) and sweet basil (in soilless conditions) showed a general overall enhancement of plant growth and quality when hydrogel was added to growing media. The tested hydrogel showed to be suitable for potential use in agriculture. Its employment should be further evaluated under a cost-effective perspective. (C) 2015 Published by Elsevier B.V.

Closed cycle soilless techniques can be adopted to minimize water and fertilizer losses in greenhousecultivation. There is a general lack of information regarding the soilless cultivation of vegetables withclosed cycle subirrigation techniques, specifically when using saline water. In this study, a trough benchsubirrigation system (SUB), with two fertilizer concentrations (''100%'', containing 9.8 mol m3 N-NO3,1.6 mol m3 P-H2PO4, 8.7 mol m3 K+, 2.8 mol m3 Ca+, 1.8 mol m3 Mg+, 4 mol m3 S-SO4, and ''70%'',containing 70% of the macronutrient concentration) in the nutrient solution (NS), was compared withopen cycle drip-irrigation (DRIP with ''100%'' NS). For all the three treatments, NS was prepared usingrain water (0.05 dS m1) and adding NaCl (1 g L1), in order to simulate moderate saline irrigation water.The effect of the treatments on tomato (Solanum lycopersicum L.) plant growth, yield, fruit quality, wateruse efficiency (WUE) and fertilizer consumption was evaluated. Substrate and recirculating NScomposition were also studied. Subirrigation, regardless of NS concentration, reduced plant height (by30 cm), leaf area (by 1411 cm2), total fresh and dry weight (by 429 and 48.5 g plant1, respectively) butnot dry matter percentage of the whole plant, with respect to DRIP. Yield was reduced when plants weresubirrigated with the higher concentrated NS, but no differences with open cycle DRIP were recordedwhen the lower NS concentration was used in SUB. Fruit quality was not affected by irrigation system orNS concentration. The higher WUE was obtained with subirrigation. NaCl accumulated similarly over thecrop cycle in recirculating NS of both SUB treatments and in growing substrates of all the threetreatments. Higher salt concentration was found in subirrigated substrates, in particular in the upperpart of the substrate profile. Fertilizers accumulated in the subirrigated substrates when the higher NSconcentration was used, but not when the NS concentration was reduced by 30%. The results of this studyindicate that tomato can be grown successfully in a closed cycle subirrigation system, using saline water,by reducing the fertilizer NS concentration normally used with traditional open cycle systems.

Residues of the marine plant posidonia (Posidonia oceanica, PO) beached in tourist zones represent a great environmental, economical, social and hygienic problem in the Mediterranean Basin, in general, and in the Apulia Region in particular, because of the great disturb to the bathers and population, and the high costs that the administrations have to bear for their removal and disposal. In the present paper, Authors determined the heating values of leaves and fibres of PO, the main offshore residues found on beaches, and, meantime, composted those residues with mowing and olive pruning wood. The final composts were characterized for pH, electrical conductivity, elemental composition, dynamic respiration index, phytotoxicity, fluorescence and infrared spectroscopic fingerprints. The aim of the paper was to investigate the composting and energy recovery of PO leaves and fibres in order to suggest alternative solutions to the landfill when offshore residues have to be removed from recreational beaches. The fibrous portion of PO residues showed heating values close to those of other biofuels, thus suggesting a possible utilization as source of energy. At the same time, compost obtained from both PO wastes showed high quality features on condition that the electrical conductivity and Na content are lowered by a correct management of wetting during the composting.

Compost has been recently suggested as an alternative to peat for the preparation of growing substrates in soilless cultivation systems. However, some physico-chemical properties of compost may reduce plant performance and endanger the quality of productions, in particular for possible heavy metal accumulation in edible parts. This study aims at evaluating the suitability of a municipal solid waste compost (MSWC) and a sewage sludge compost (SSC) as components of growing media for the soilless cultivation of lettuce (Lactuca sativa L.). Heavy metal content of SSC complied with legislation limits but, in MSWC, it exceeded (Cu, Pb) or was very close (Cd, Zn) to safe limits. A greenhouse experiment was carried out by cultivating four lettuce cultivars ("Maximus," "Murai," "Patagonia," and "Aleppo") in pots containing a mixture of MSWC and perlite (MSWC + P), SSC and perlite (SSC + P), or peat and perlite (peat + P), the latter used as control. Plant biometric parameters measured after 72days of growth revealed that the yield of plants cultivated on SSC + P was similar to control plants, independently of the cultivar. Conversely, MSWC + P suppressed in general the biomass production, especially for Murai and Patagonia cultivars. Compared to peat + P, both compost-based substrates reduced the leaf accumulation of heavy metals, with a major effect in Maximus plants. The levels of Cd and Pb in the edible part were always below the safe limits imposed by European regulation. Therefore, risks of heavy metal intake in food chain associated with the replacement of peat with compost in the growing media are negligible, even when a compost with a significant amount of heavy metals is used. Besides compost quality monitoring, also an appropriate varietal choice is crucial to obtain good yields and safe products.

Anaerobic digestion is a technique of growing interest as a promising option for waste disposal and green energy production. The anaerobic effluents (digestate) are a mixture of water (about 95 %) and partially degraded organic matter. Afterwards separation of the two components (liquid and solid), the inorganic ions with a fertilizer value are concentrated mainly in the liquid one. The main limitation to their agricultural use could be the sodium chloride content derived from the initial matrices and the potential phytotoxicity originated from partially decomposed organic matter. In this study the main agrochemical characteristics and the phytotoxicity of eight digestates (derived from co-digestion of posidonia residues with different pretreatments - grinding, washing and autoclave treatments - and a mixture of urban sludges and organic wastes) were evaluated in order to assess their potential use as a source of water and nutrient elements in vegetable seedling production.Lettuce (Lactuca sativa L. var. Ezra) seedlings for transplant were produced on peat based substrate. Digestates liquid fraction (LD), obtained after centrifugation, was used to integrate the nutrient solution at rate of 1:10 v/v; a standard nutrient solution for lettuce seedling cultivation was used as a control (NS). Main chemical properties (pH, EC, inorganic ions content) of LD, shoot and root fresh and dry weight, leaf area, root morphology, root/shoot ratio were determined. Different content of Cl- and Na+ were found in LD in relation to the posidonia residues pre-treatment; moreover LD contained in general high concentration of NH4+, K2+, Mg2+ and Ca2+. Plants cultivated using LD showed a root/shoot ratio (important to ensure good engraftment after transplanting) not significally different from plants grown with NS. The use of LD produced a fresh water saving of 10% and the reduction of mineral fertilizers use. The liquid fraction of digestates could be a good source of macro nutrients and water, and first results indicate that could be re-utilized in relation to its salts content as nutrient solution for lettuce seedling production and likely in soilless cultivation systems.

Irrigation is a crucial practice that operators often perform empirically, relying on their own experience, especially in productive areas characterized by low technology agriculture (i.e. several parts of Mediterranean countries). One of the possible approach for proper irrigation scheduling is measuring the soil water potential, simple and easy to manage. The purpose of this research was to examine the effects of two different irrigation regimes (obtained by the use of tensiometer connected to a relay controller) on yield, fruit quality and water consumption of greenhouse tomato (Solanum lycopersicum L. 'Naxos') and cucumber (Cucumis sativus L. 'Sarig' in the first cropping cycle, and 'Mezzo lungo di Polignano', a local landarace, in the second one) grown on a silty-clay soil in Mediterranean conditions. For each species, two tests (August-February and February-July cycle) were carried out in a plastic greenhouse-tunnel. Drip irrigation was adopted, with automated schedule based on tensiometer readings. Two water potential irrigation set-points were compared: -100 and -400 hPa for tomato and -100 and -300 hPa for cucumber, in both cycles. Yield (marketable and unmarketable) and quality traits of fruits (soluble solids, dry matter and titratable acidity) were determined. Water consumption was calculated at the end of each crop cycle. In the first cycle, the two water regimes did not affect the yield of tomato and cucumber. The cucumber irrigated at the lowest soil water potential set-point produced fruits with 8% higher dry matter. In the second cycle, the tomato irrigated at the potential of -400 hPa showed a 40% lower yield (mainly due to the lower fruit size) compared to that of plants irrigated at -100 hPa. The fruits of tomato plants irrigated at -400 hPa, however, showed total soluble solids, dry matter and titratable acidity respectively 41, 45 and 59% higher than -100 hPa. On average, in both crop cycles, a water saving of 35% and 46% on average for tomato and cucumber, respectively, was obtained using the lowest potential as irrigation set-point.Proper use of tensiometer could allow a better use of water resource. Selection of proper water potential set-points according to the cultivation season is crucial for satisfactory results. The positive effects of a controlled and moderate water stress on fruit quality should be taken into account.

Posidonia (Posidonia oceanica [L.] Delile) is a marine phanerogam endemic of the Mediterranean basin. Senescent plant parts periodically detach from and accumulate along Mediterranean beaches, forcing the coastal municipalities to remove and manage somehow the large amount of beached biomass. In this research, a posidonia based compost (posidonia, 63% by volume - olive tree pruning residues, 21% - green waste, 16%) has been used as growing media component at different ratios (0, 25, 50, 75 and 100%), as a complement to a peat based commercial substrate, for nursery lettuce seedlings production. Growing media with increasing compost percentage showed higher pH, EC, air capacity and nutrients availability, but lower water holding capacity. The overall growth of the seedlings was enhanced by the compost presence in the substrate, with positively evidences for both roots and leaves. Posidonia based compost could represent an interesting alternative to peat as horticultural growing media component.

A new sensor for the measurement of electrical conductivity (EC) and moisture content, specifically designed for soilless substrates, has been released (GS3, Decagon Devices). The Hilhorst equation has been proposed as a tool to convert the measured bulk EC (ECb) into the pore EC (ECp, the EC of the solution in the pore spaces of the substrate). A test was carried out to verify the ability of the GS3 sensors to measure changes in the substrate EC under realistic cultivation conditions. Pots, containing tomato plants growing in perlite, were subjected to irrigation for about four weeks with a schedule set to have a leaching fraction of about 90%, which enabled the maintenance of very similar EC in both the root zone and the drainage solutions. A low and a high EC nutrient solution (EC = 2.4 and 4.1 dS/m, respectively) were used in the first and the second half of the test, respectively. The EC of the leachate, used as a measure of the real substrate ECp (ECpreal), the ECb measured by the GS3 sensors and the resulting ECp calculated with the Hilhorst equation (ECpHilhorst) were recorded during the test. The three parameters (ECb, ECpreal and ECpHilhorst) all showed the trend of increasing salinity in the substrate. However, both ECb and ECpHilhorst resulted in different values, in absolute terms, compared to the ECpreal provided by the measurement of the leachate. In particular, the ECpHilhorst values were always lower than ECpreal (0.60 vs 2.48 dS/m and 1.10 vs 4.68 dS/m, on average, respectively in the first and second half of the test).However, the ECpHilhorst was correlated in the tested EC range with the real ECp in the substrate (ECpreal = 4.2815×ECpHilhorst - 0.0766, R2=0.99). According to our results, it seems that GS3 sensors used in perlite are not able to provide accurate values of ECp simply by applying the Hilhorst equation. However, the values provided by the sensor are correlated with the real ECp of the substrate; therefore, using a proper second-step equation can help to convert the obtained value into the real ECp of the substrate.

There is a need for sustainable fertilizers because common mineral fertilizers are increasingly costly and often induce water and air pollution. For instance, seagrass compost could be used as fertilizer in the coastal areas of the Mediterranean, thus also solving the issue of beached resi- dues. Here, we studied organic fertilization by application of seagrass-based compost in a tomato and lettuce crop succes- sion. Composts were made of posidonia and yard wastes at 1/4 w/w fresh weight ratio. Compost was applied at two concentrations: 10 and 20 Mg ha-1 fresh weight. Fresh leaves of posidonia were also tested directly as organic mulch in plots treated with conventional fertilizers. A control treatment in- volved mineral fertilization without mulching soil. Herbicide applications were performed in non-mulched plots immedi- ately before transplanting of tomato and lettuce for controlling the weeds, while mulched treatments did not receive any herbicide application. Results show that 20 Mg ha-1 of posidonia-based compost is equivalent to the inorganic fertil- ization because the nutritional status and yield of tomato and lettuce were statistically similar. No phytotoxicity symptoms were observed in any of the tomato and lettuce plants mulched with posidonia. The same growth rate was observed for toma- to and lettuce growing under conventional management prac- tices: mineral fertilizer and herbicide applications. Overall, our findings show that seagrass-based compost is a promising, sustainable fertilizer for tomato and lettuce.

Peat is the main component of growing media but is also a non-renewable resource; therefore European policy strongly encourages the use of peat alternatives such as compost. Posidonia is a Mediterranean seagrass that produces very conspicuous onshore deposits that can be composted. In this study, a commercial green compost and a Posidonia residue-based compost were tested in order to assess their potential use as substitutes or complements to peat.RESULTS:All macro and micro-element concentrations of the substrates were positively and significantly related to the percentage of composts in the growing media. Plant grown on peat showed higher content of P, Ca, K, Na, Cu, Mn, Zn and Fe, and a slightly higher biomass production in comparison to compost-based growing media. In contrast, plants grown on compost-based substrates showed lower uptake of Cd and Cr than peat.CONCLUSION:The results indicate that both composts can be used as a complement to the peat for substrate preparation, especially at a rate of 30%. The Posidonia-based compost showed better productive results in comparison to the green one. Basil grown on the two compost-based media showed reduced absorption level of potentially toxic metals in comparison to peat.

Posidonia [Posidonia oceanica (L.) Delile] is a marine phanerogam endemic of the Mediterranean Sea that grows all along the coast forming extensive underwater meadows. Senescent posidonia leaves, together with fibers (residues of rhizomes and decomposed leaves), periodically accumulate along Mediterranean beaches, covering vast areas of coast. Removal and disposal of these large volumes of plant biomasses represent a high cost for local administrations. Therefore, in this experiment, beached residues of posidonia were composted with olive pruning and green wastes with the objective to assess the efficacy of posidonia-based compost (63% on a volume basis) as a peat replacement. The compost was then mixed with a peat-based commercial substrate at rates of 0% (C0, pure peat-based commercial substrate tested as control), 25% (C25), 50% (C50), 75% (C75), and 100% (C100, pure posidonia-based compost) v/v. Mixtures were used as growing media to produce lettuce seedlings for transplant. Two lettuce cultivars (8511RZ and Satine) were tested. Main physical and chemical properties of the five growing media, shoot and root fresh and dry weight, leaf area, root morphology, and elemental leaf tissue composition were studied. Growing media containing posidonia-based compost, C25 and C50 in particular, showed good physical properties. Increasing compost proportions in the mixtures resulted in enhanced: 1) availability of macro- and micronutrients in the growing media; and 2) overall growth parameters of lettuce seedlings, in particular for the cultivar Satine. In conclusion, posidonia-based compost shows a considerable potential as a peat substitute in horticultural substrates; posidonia residues are a low-cost renewable material. In growing media for lettuce seedlings production, posidonia-based compost could be used as a complement to peat at a rate of 25% or 50% to obtain optimal physical properties and to limit the negative effects of high B content, which are typical of posidonia residues.

High quality compost could be used as an environmentally friendly and renewable component for soilless growing media. Beached residues of posidonia (Posidonia oceanica (L.) Delile), a marine phanerogam endemic to the Mediterranean Sea, can be used as raw material for compost production. The aim of this study was to evaluate a posidonia-based compost as a soilless growing medium component for the cultivation of tomato. Beached residues of posidonia (20% in weight) and green wastes were composted. The compost, alone (Compost 100%) or mixed with perlite at the rate of 50% in volume (Per-Comp 50:50), was used as growing medium and compared with traditional perlite (Perlite 100%). Tomato plants (cv. 'Ikram' ungrafted, 'Ikram' grafted onto 'Beaufort' and 'Ikram' grafted onto 'Arnold') were grown in the three growing media. A complete nutrient solution (EC = 1.7 dS/m; pH = 5.0) was used for fertigation. A system composed by EC5 soil moisture sensors, a data logger and a rely controller, and tensiometers to check water potential was used to manage fertigation, with the aim to maintain easily available water. Forty five days after transplanting, the plants grown in 100% compost as well as in the compost/perlite mix resulted in higher growth. Leaf area, total fresh and dry weight increased with increasing amounts of compost in the substrate. The tomato yield in Compost 100% and Per-Comp 50:50 treatments resulted higher than Perlite 100%, in terms of weight and number of fruits (15 and 7%, respectively). Grafted plants, regardless of the rootstock, showed a higher total yield if compared with ungrafted plants (11%, on average). The quality profile of fruits was only slightly influenced by growing media, while was not by the grafting combination. The results show that the compost-based posidonia could be successfully used as soilless substrate component for growing tomato.

This study aimed to determine the effects of irrigation management based on matric potential control on growth, plant-water relations, yield, fruit quality traits and water-use efficiency of subirrigated (through bench system) soilless tomato. Tensiometers were used for automatic irrigation control. Two cultivars, 'Kabiria' (cocktail type) and 'Diana' (intermediate type), and substrate water potential set-points (-30 and -60 hPa, for 'Diana', and -30, -60 and -90 hPa for 'Kabiria'), were compared. Compared with -30 hPa, water stress (corresponding to a -60 hPa irrigation set-point) reduced water consumption (14%), leaf area (18%), specific leaf area (19%), total yield (10%) and mean fruit weight (13%), irrespective of the cultivars. At -60 hPa, leaf-water status of plants, irrespective of the cultivars, showed an osmotic adjustment corresponding to a 9% average osmotic potential decrease. Total yield, mean fruit weight, plant water and osmotic potential decreased linearly when -30, -60 and -90 hPa irrigation set-points were used in 'Kabiria'. Unmarketable yield in 'Diana' increased when water stress was imposed (187 vs 349 g?plant-1, respectively, at -30 and -60 hPa), while the opposite effect was observed in 'Kabiria', where marketable yield loss decreased linearly [by 1.05 g?plant-1 per unit of substrate water potential (in the tested range from -30 to -90 hPa)]. Whereas in the second cluster, fruit total soluble solids and dry matter increased irrespective of the cultivars, in the seventh cluster in 'Diana' only a slight increase was observed from -30 vs. -60 hPa (3.3% and 1.3%, respectively, for TSS and dry matter), while in 'Kabiria' the increase was more pronounced (8.7% and 12.0%, respectively, for TSS and dry matter), and further reduction in matric potential from -60 to -90 hPa confirmed the linear increase for both parameters. Both glucose and fructose increased linearly in 'Kabiria' fruits on decreasing the matric potential, while in 'Diana' there was no increase. Control of substrate water status offer the possibility to steer crop response by enhancing different crop-performance components, namely yield and fruit quality, in subirrigated tomato. Small-size fruit varieties benefit more from controlled water stress in terms of reduced unmarketable yield loss and fruit quality improvements.

Posidonia oceanica (L.) Delile is the main marine seagrass endemic of the Mediterranean Sea. From September on, leaves and rhizomes detach off the marine plant and accumulate on beaches in huge amounts, forming banks on the foreshore and backshore of beaches. Offshore residues represent an environmental, economical, social and hygienic problem, because of the great disturbance to the touristic activities, citizens life in urban areas and high costs that the public administrations have to support for managing them (beach cleaning, transport and disposal of such a biomass). Nowadays, current Italian legislation (n. 75/2010) allows the use of posidonia residues as raw material for the production of compost although at a maximum rate of 20% by fresh weight of the composting mixture. High presence of sand mixed to residues after removing from beaches and high salinity levels represent at the moment the main obstacles to the large use of this biomass as raw material for composting. Studies have been conducted, in the framework of the Life09 "Posidonia Residues Integrated Management for Eco-sustainability" (P.R.I.M.E.) project, with the aim to increase the application of posidonia residues for compost production, demonstrating the possibility to effectively separate the sand from the organic material and reduce the salinity levels. Several tests have been carried out with the objective to assess the posidonia-based compost quality. Posidonia-based compost proved to be a good peat substitute for lettuce transplant production and a good growing media component for greenhouse tomato and lettuce in soilless conditions. According to our studies, beached posidonia wastes could represent a low cost and renewable raw material for composting. Posidonia-based compost presents interesting properties and can be used as horticultural growing media component.

Peat is a non-renewable resource and its extraction contributes to the degradation of wetland ecosystems. In order to reduce the peat use in nursery, two composts prepared from yard wastes were evaluated as a substrate component for producing vegetable seedlings for transplantation. Two experiments with tomato (Solanum lycopersicum L.) cultivars 'Naxos' and 'TCP 9147' and pepper (Capsicum annuum L.) cultivars 'Solero' and 'Logos' were set up in a greenhouse. In each experiment two composts were tested: "Cp", obtained from yard wastes + beached residues of marine plant posidonia [Posidonia oceanica (L.) Delile - 20% of total fresh weight], and "C", obtained only from yard wastes. Each compost was mixed with commercial peat in the amount of 0 (control), 25, 50, 75 and 100% (v/v). Results from the study suggest that, for both species, the best yield was obtained with the substrate prepared by mixing the peat with 25% of Cp.

We compared the effects of: 1) timer- ('Timer') and soil moisture sensor-controlled irrigation on soilless lettuce; 2) two volumetric water content (?) thresholds for irrigation (0.30 ('?=0.3') and 0.40 m3?m-3 ('?=0.4')). The most nutrient solution (NS) was applied in 'Timer' where the lowest water use efficiency was observed, with 17 and 42% less NS used in '?=0.4' and '?=0.3', respectively. Irrigation volumes followed the plant water needs in the sensor-controlled treatments, with little or no leaching, while 18% of leaching was recorded in 'Timer'. Plants in 'Timer' and '?=0.4' had higher fresh weights (24%) and leaf area (13%) than plants in ?=0.3. Similar dry weight was observed among treatments but percent dry matter was 20% higher in '?=0.3'. Gas exchanges and leaf tissue chemical composition were similar in all treatments, but nitrate concentration was lower in the '?=0.3' plants. Precision sensor-controlled irrigation based on ? measurements is an effective tool to increase the overall WUE and to improve the quality of soilless-grown lettuce by acting on the substrate moisture level.

The increasing availability of low-cost and reliable substrate moisture sensors offers interesting perspectives for rational and automatic rrigation management of soilless greenhouse crops and for research on plant water relations. The knowledge of the effects of different substrate volumetric water content (VWC) levels on plant growth is crucial for the determination of proper irrigation set-points. An experiment was conducted to assess the effects of different VWC levels on soilless tomato growth and water relations. Tomato plants were grown in a greenhouse in perlite bags. An automatic irrigation system used substrate moisture sensors to control irrigation solenoid valves, in order to keep growing media at four different VWC levels (0.15, 0.20, 0.25 and 0.30 m3?m-3). The system was able to get the substrate VWC at the desired different set-points. Substrate water potential was monitored during the experiment using tensiometers. The four VWC levels resulted, respectively, in a mean substrate water potential of -130, -101, -42 and -34 hPa. Plant growth was similar for plants grown at 0.30 and 0.25 m3?m-3 in terms of leaf area, fresh and dry weight, with higher values than plants grown at 0.20 and 0.15 m3?m-3. Plant water status was affected by the VWC level in the substrate, with higher and similar values of total leaf water potential for plants grown at the two highest VWC levels thanthose grown at lower VWC. The most severe effects of water stress were observed on plants grown at 0.15 m3?m-3 which showed the lowest leaf relative water content (respectively 64.4% vs 84.8% at higher VWC levels) and membrane stability index (respectively 68.6% vs 83.9% at higher VWC levels). The water retention curve and hydraulic conductivity analysis performed on the perlite substrate used in this experiment revealed little or no available water below a VWC of about 0.15 m3?m-3. However, plants grown at 0.15 m3?m-3, were able to uptake water from the growing media and thus to survive, although showing reduced growth and symptoms of water stress. Results seem to confirm that soilless growing media generally hold easily available water in a matric potential range from 0 to -100 hPa, with the majority of free available water present between matric potentials of 0 to -50 hPa.