Development of know-how and technology for the cultivation of greenhouse crops in closed hydroponic systems aimed at preventing nitrate pollution and use of chemical soil fumigants
Co-funded by the EU and the Greek Ministry of Education and Religions in the framework of Archimedes I (project code: 10008 – 00002)
Duration of the project: 01/01/2003 to 12/31/2006.
Project leader: Dr. Savvas D.
Team members (A-Z):
Albanis T., Bakea M., Barouchas P., Chatzieustratiou E., Giotis D., Gizas G., Karras G., Katsoulas, N., Kittas C., Kotsiras A., Kyrkas D., Lydakis-Simantiris N., Maglaras L., Mantzios N., Margariti S., Matakoulis C., Meletiou G., Moustaka E., Nasi E., Olympios C., Papadimitriou M., Pappa V.A., Passam H.C., Patakioutas G., Sakellarides T., Salahas G., Stamati E., Tsirogiannis I.L., Tsouka N.
Development of know-how and technology for the cultivation of greenhouse crops in closed hydroponic systems aimed at preventing nitrate pollution and use of chemical soil fumigants. A number of relevant experiments were conducted in greenhouse environment and concerned both ornamental plants and vegetables. Special models for close-loop hydroponic cultivation were evaluated and updated in order to combine optimum yield in both quantitive and qualitive terms along with the less possible need for nutrient solutien withdrawn. All the results were published in international scientific peer review journals or presented in international conferences.
D. Savvas, D. Giotis, E. Chatzieustratiou, M. Bakea, G. Patakioutas, 2008. Silicon supply in soilless cultivations of zucchini alleviates stress induced by salinity and powdery mildew infections. Environmental and Experimental Botany, 65, 11-17
In the present study, the hypothesis was tested as to whether silicon supplied via the nutrient solution is capable of enhancing the tolerance of hydroponically grown zucchini squash (Cucurbita pepo L., cv. ‘rival’) to salinity and powdery mildew infections. Two experiments were conducted involving a low (2.2 dS m-1, 0.8 mM NaCl) and a high salinity level (6.2 dS m-1, 35 mM NaCl) in combination with a low (0.1 mM) and a high (1.0 mM) Si level in the nutrient solution supplied to the crop. The exposure of the plants to high external salinity restricted significantly the vegetative growth as well as the fruit yield of zucchini due to a reduction of both the number of fruits per plant and the mean fruit weight. However, the combination of high salinity with a high Si level mitigated the growth suppression and resulted in a significant increase of yield due to an increase of the fruit number per plant in comparison with the low Si supply at the same salinity level. Part of the growth and fruit yield suppression at high salinity was due to restriction of net photosynthesis. The stomatal conductance was also restricted by salinity, whereas the substomatal CO2 concentration was not affected by the NaCl or Si treatments. The supply of 1 mM of Si via the nutrient solution mitigated the inhibitory effect of salinity on net photosynthesis and this effect was associated with lower Na and Cl translocation to the epigeous plant tissues when the high salinity was combined with a high Si level. Furthermore, the supply of Si via the nutrient solution suppressed appreciably the expansion of a powdery mildew (Spaerotheca fuliginea) infection in the leaves at both salinity levels. These results indicate that silicon is capable of alleviating the adverse salinity effects on zucchini squash and enhancing crop resistance to powdery mildew, when it is supplied via the nutrient solution in soilless culture.
Savvas, D., Stamati, E., Tsirogiannis, I.L., Mantzos, N., Barouchas, P., Kittas, C., Katsoulas, N., 2007. Interactions between salinity and irrigation frequency in greenhouse pepper grown in a closed-loop hydroponic system. Agricultural Water Management, 91: 102-111
Two different irrigation regimes with two different salinity levels were applied to peppers (Capsicum annum L.) grown in closed hydroponic systems in a glasshouse. The two salinity levels were attained by adding NaCl to the irrigation water used to prepare nutrient solution to obtain concentrations of 0.8 and 6 molm 3, and allowing the salts to progressively accumulate in the recycled nutrient solution. The two salinity levels were combined with two different levels of irrigation frequency in a two-factorial experimental design. Initially, the Na and Cl concentrations increased rapidly in the recycled effluents, but nearly three months after treatment initiation they converged gradually to maximal levels depending on the NaCl treatment. The low irrigation frequency imposed a more rapid salt accumulation in the root zone, which was ascribed to restriction of the volume of drainage solution. However, the maximal salt concentrations in the root zone were independent of the watering schedule. This finding agrees with previous research revealing that the maximal salt accumulation in the root zone of plants, grown in closed hydroponics, is dictated merely by the NaCl concentration in the irrigation water. Total and Class I yields were suppressed by salt accumulation but the high irrigation frequency significantly mitigated the deleterious salinity effects. At low salinity, the low irrigation frequency raised significantly the weight percentage of fruits with blossom-end rot (BER), whereas at high salinity the incidence of BER was further increased without significant differences due to the irrigation regime. Frequent irrigation resulting in high drainage fractions in closed hydroponic systems may delay the rate of salt accumulation in the root zone, thereby enhancing yield and improving fruit quality, without increasing the discharge of polluting fertigation effluents to the environment.
Savvas, D., Gizas, G., Karras, G., Lydakis-Simantiris, N., Salahas, G., Papadimitriou, M., Tsouka, N., 2007. Interactions between silicon and NaCl-salinity in a soilless culture of roses in greenhouse. European Journal of Horticultural Science 72, 73-79
In an experiment with roses grown hydroponically, a low (0.3 mM) and a high (2 mM) level of silicon were combined with a low (0.8 mM) and a high (40 mM) NaCl concentration in the nutrient solution supplied to the crop. The aim of the experiment was to detect possible beneficial effects of silicon on plant growth, yield and flower quality and to test whether the deleterious effects of NaCl-salinity on roses could be mitigated by increasing the Si concentration in the root zone. Silicon was added to the nutrient solution in form of a water- soluble potassium silicate compound. The electrical conductivity (EC) in the nutrient solutions with low and high NaCl concentrations was 1.8 and 6.1 dS m–1, respectively, while the corresponding values in the drainage water, which indicated the salinity status in the root zone, were 2.3 and 8.2 dS m–1, respectively. The increase of the NaCl concentration in the root zone restricted the above-ground vegetative weight of roses, the number of flowers per plant and the mean flower weight and stem length. The increased supply of Si significantly enhanced the vegetative growth of roses at both salinity levels, improved the overall appearance of the plants and resulted in a higher number of marketable flowers per plant at the low salinity level. However, silicon was unable to ameliorate the adverse effects of NaCl-salinity on flower production and quality. The increased Si concentration in the root environment restricted the translocation of Na and Cl to the young leaves of roses. However, net photosynthesis, stomatal conductance and transpiration rate were not affected either by Si or by NaCl-salinity at the concentration levels tested in this study. This finding indicates that the stimulation of the vegetative growth of roses by Si under conditions of high external salinity was not due to mitigation of toxic Na or Si effects on the photosynthetic apparatus.
Patakioutas G., Savvas D., Matakoulis C., Sakellarides T., and Albanis T., 2007. Application and Fate of Cyromazine in a Closed-Cycle Hydroponic Cultivation of Bean (Phaseolus vulgaris L.). J. Agric. Food Chem. 55(24):9928-35
The fate of cyromazine applied via the nutrient solution (20, 40, and 60 mg of active ingredient per plant) in a closed-cycle soilless cultivation of bean with zero discharge of effluents was traced in both the recycled drainage solution and the plant tissues for 99 days. The insecticide was applied once, 15 days after planting (16 days prior to the first harvest). In addition to cyromazine, the residues of melamine, its metabolite, in the drainage solution and plant tissues were also regularly determined during the 99 days. The two higher application doses induced toxicity symptoms on the leaves of the bean plant. The maximum cyromazine levels were measured 8 days after application in the drainage solution (17–46 mg l-1), 16 days in the roots (1.1–2.4 mg kg-1 fresh weight [f. wt.]) and the vegetative shoot (4.5–9.5 mg kg-1 f. wt.), and 24 days after application in the pods (2.6–4.1 mg kg-1 f. wt.). However, the cyromazine residues in pods were clearly below the maximum acceptable levels for bean. The half-life of cyromazine in the drainage solution ranged from 16 to 19 days for the three doses. The melamine residues in the drainage solution and in the roots reached a concentration peak 16 days after cyromazine application, whereas in the vegetative shoot and the pods they were constantly increasing over the 99 days after application. Nevertheless, the melamine residues were constantly much lower than those of cyromazine, although on the last sampling day (99) they tended toward convergence. Cyromazine proved to be highly persistent, as indicated by the remarkably high residues measured in both the drainage solution and the plant tissues, even 99 days after application.Nevertheless, the application of cyromazine via the nutrient solution to beans grown in closed-cycle hydroponic systems at doses not exceeding 20 mg per plant seems to be safe with respect to both phytotoxicity and residue levels in the edible pods.
Katsoulas N., C. Kittas, I. L. Tsirogiannis, E. Kitta, D. Savvas, 2007. Greenhouse microclimate and soilless pepper crop production and quality as affected by a fog evaporative cooling system. Transactions of the ASABE, Vol. 50(5): 1831-1840
The influence of greenhouse humidity control on greenhouse microclimate, crop transpiration rate, and yield and fruit quality of a soilless grown pepper crop was studied in a greenhouse located at the coastal area of western Greece. Measurements were carried out during summer and autumn in two distinct greenhouse compartments involving: (1) no air humidity control and (2) a fog system operating when the relative humidity of the greenhouse air was lower than 80%. Under fog conditions, the greenhouse air and the crop leaf temperature were about 3°C lower than those measured under no fog conditions. The fog system allowed maintenance of the greenhouse air temperature under 30°C, while a maximum value of about 35°C was reached under no fog conditions. In addition, under fog conditions, the air vapor pressure deficit was lower than 2 kPa, even during the warmest part of the day, while under no fog conditions it reached values near 4 kPa. However, the transpiration rate was not affected to such an extent by fog as the air vapor pressure deficit, and under fog conditions it decreased by about 26%. This is attributed to the values reached by the bulk stomatal conductance, which were about 1.5 times higher under fog than under no fog conditions. The crop leaf area index values observed after the middle of the experimental period and later, under fog conditions, were higher than that observed under no fog conditions. Finally, the fog system enhanced the mean fruit weight and the percentage of marketable fruits but reduced appreciably the total number of fruits per plant. The free (titratable) acidity and the total soluble solids in the pepper fruit sap were slightly reduced by the fog cooling system, while the fruit size was increased. The use of a fog cooling system proved to be beneficial for summer crops of pepper grown under Mediterranean climatic conditions due to a favorable impact of the reduced vapor pressure deficit on both the mean fruit weight and the quality in terms of fruits graded Class I. Nevertheless, the high air humidity imposed by a cooling fog system may reduce the number of fruits per plant, thereby offsetting the benefits from the increased mean fruit weight in terms of total yield.
Katsoulas, Ν., E. Kitta, C. Kittas, I.L. Tsirogiannis, E. Stamati, D. Savvas, 2006. Greenhouse Cooling by a Fog System: Effects on Microclimate and on Production and Quality of a Soilless Pepper Crop. Acta Horticulturae 719: 455-462
The influence of greenhouse humidity control on greenhouse microclimate, crop transpiration rate, and yield and fruit quality of a soilless grown pepper crop was studied in a greenhouse located in the coastal area of western Greece. Measurements were carried out during summer and autumn in two distinct compartments involving: (i) no air humidity control and (ii) a fog system operating when the relative humidity of the greenhouse air was lower than 80%. Under fog conditions, the greenhouse air and the crop leaf temperature were about 3oC lower than those measured under no fog conditions. In addition, under fog conditions, the air vapour pressure deficit was lower than 2 kPa, even during the warmest part of the day. Furthermore, the use of a fog system reduced crop transpiration by about 20%. The fog system enhanced the mean fruit weight and the percentage of marketable fruits but reduced appreciably the total number of fruits per plant. The acid content and pH of the pulp juice of pepper fruits were not affected by the fog cooling system, while the soluble solids of the fruits were slightly reduced and the volume of the fruits was increased.
Savvas, D., Nasi, E., Moustaka, E., Mantzos, N., Barouchas, P., Passam, H.C., Olympios, C., 2006. Effects of ammonium nitrogen on lettuce grown on pumice in a closed hydroponic system. HortScience 41(7):1667–1673
Two successive lettuce crops were grown in spring 2005 in a completely closed hydroponic system. The ratio of ammonium to total nitrogen (Nr) in the fresh nutrient solution (FNS) introduced into the closed system to compensate for plant uptake was 0, 0.1, 0.2 and 0.3 on a molar basis. In all Nr treatments, the concentrations of total N, K, Ca, Mg, P, and micronutrients in the FNS were identical, but that of SO4 2– increased as Nr increased, to compensate electrochemically for the enhanced NH4+ and decreased NO3– supply. The highest fresh and dry weights per plant were attained with the highest ammonium supply (Nr = 0.3) but, even when no NH4+ was included in the FNS as an N source, the plants were healthy without apparent nutritional disorders. The ammonium concentration in the drainage solution dropped to nearly zero in all treatments some days after the initiation of recycling, which implies a preferential uptake of NH4-N over NO3-N. The root zone pH, as indicated by the values measured in the drainage solution, decreased slightly as Nr increased, and ranged from 6.5 to 8.0 in all treatments. The leaf K, Ca, Mg, and Fe concentrations were not influenced, whereas those of P, Mn, Zn, and Cu were enhanced by the increasing NH4+ supply. The increased ammonium supply did not enhance the utilization of N in plant metabolism, although it reduced the nitrate concentration of the internal leaves in the early spring experiment. The leaf micronutrient concentrations were clearly more than critical levels even when NO3– was the sole N source for lettuce, whereas the P concentration approached the lowest critical level when Nr was 0 or 0.1. The stimulation of lettuce growth as Nr was increased to 0.3 may be a consequence of enhanced P uptake resulting from better control of pH in the root zone.
Link (PDF): http://hortsci.ashspublications.org/content/41/7/1667.full.pdf
Savvas, D., Mantzos, N., Barouchas, P., Tsirogiannis, I., Olympios, C. and Passam, H.C., 2006. Modeling Salt Accumulation by a Bean Crop Grown in a Closed Hydroponic System in Relation to Water Uptake. Scientia Horticulturae, 111 (2007) 311–318
Four different NaCl concentrations in the irrigation water, 0.8, 3, 6 and 9 mol m-3, were applied as experimental treatments to beans (Phaseolus vulgaris L.) grown in completely closed hydroponic systems in a greenhouse. Initially, the Na and Cl concentrations increased rapidly in the root zone, as indicated by the values measured in the drainage water, and this resulted in corresponding increases in the Na/water and Cl/water uptake ratios. However, as these ratios approached equilibrium with the NaCl/water ratios in the irrigation water, the Na and Cl concentrations in the root zone converged to maximal levels, which depended on the treatment. The highest Na and Cl concentrations in the root zone and the corresponding NaCl concentrations in each treatment were used to establish relationships between the external NaCl concentration and the Na/water or Cl/water uptake ratios, which proved to be exponential for Na but linear for Cl. These relationships were then used in a previously established model.
Savvas, D., V.A. Pappa, A. Kotsiras, G. Gizas, 2005. NaCl accumulation in a cucumber crop grown in a completely closed hydroponic system as influenced by NaCl concentration in irrigation water. European Journal of Horticultural Science, 70, 217-223
Four different NaCl concentrations in the irrigation water, 0.8, 5, 10 and 15 mM, were applied as experimental treatments to cucumber (Cucumis sativus L.) grown in a closed hydroponic system. These treatments were attained by automatically injecting the required amounts of NaCl into irrigation water containing 0.8 mM NaCl, whenever water was mixed with fertilizers and drainage solution to prepare fresh irrigation solution. Initially, the Na+ and Cl– concentrations increased rapidly in both the fresh nutrient solution supplied to the crop and the drainage water, but they were stabilized to maximal levels depending on the treatment 45–55 days after initiation of solution recycling. It was concluded that the Na+ and Cl– concentrations in the root zone were maximized as soon as the Na/water and Cl/water uptake ratios reached equal levels with the NaCl concentration in the irrigation water. Based on these data, relationships between the Na/water or Cl/water uptake ratios and the NaCl concentration in the root zone were established. The leaf Na+ and Cl– concentrations were influenced by both the external Na+ and Cl– concentrations and the season. The Cl:Na uptake ratio (mol basis) was higher than 1 at low external NaCl concentrations but decreased below 1 as salinity increased, thereby indicating a more rapid decline in the ability of the plant to exclude Na+ from the leaves as compared to that for Cl–.
Link (pdf): http://www.pubhort.org/ejhs/2005/file_60714.pdf
Savvas, D., A. Kotsiras, G. Meletiou, S. Margariti, I. Tsirogiannis, 2005. Modeling the relationship between water uptake by cucumber and NaCl accumulation in a closed hydroponic system. HortScience, 40: 802-807
In a completely closed hydroponic system, Na and Cl commonly accumulate in the root zone, at rates depending on the concentration of NaCl in the irrigation water (rate of Na and Cl inlet) and the Na to water and Cl to water ratios at which they are taken up by the plants (rates of Na and Cl outlet). However, while the concentration of NaCl in the irrigation water is commonly a constant, the Na to water and Cl to water uptake ratios are variables depending on the concentrations of Na and Cl in the root zone and, hence, on the rates of their accumulation. To quantify this feed-back relationship, a differential equation was established, relating the rate of Na (or Cl) accumulation to the rate of water uptake. This equation was solved according to the classical Runge-Kutta numerical method using data originating from a cucumber experiment, which was conducted in a fully automated, closed-loop hydroponic installation. Four different NaCl concentrations in the irrigation water, 0.8, 5, 10 and 15 mM, were applied as experimental treatments. The theoretically calculated curves followed a convex pattern, with an initially rapid increase of the Na and Cl concentrations in the root zone and a gradual leveling out as the cumulative water consumption was rising. This was ascribed to the gradual approaching of the Na to water and Cl to water outlet ratios via plant uptake, which were increasing as NaCl was accumulating in the root zone, to the constant NaCl to water inlet ratio (NaCl concentration in irrigation water). The model could predict the measured Na and Cl concentrations in the drainage water more accurately at 10 and 15 mM NaCl than at 0.8 and 5 m.M NaCl in the irrigation water. Possible explanations for these differences are discussed. Plant growth and water uptake were restricted as salinity was increasing, following a reverse pattern to that of Na and Cl accumulation in the root zone. The leaf K, Mg and P concentrations were markedly restricted by the increasing salinity, while that of Ca was less severely affected.
Link (pdf): http://hortsci.ashspublications.org/content/40/3/802.full.pdf
Savvas, D., V.A. Pappa, G. Gizas and L. Maglaras, 2004. Influence of NaCl concentration in the irrigation water on salt accumulation in the root zone and yield in a cucumber crop grown in a closed hydroponic system. Acta Horticulturae, 697: 93-99
The effects of four different NaCl concentrations in the irrigation water used to replenish the transpiration losses in a cucumber (Cucumis sativus L.) crop grown in a closed hydroponic system were investigated for 4 months in a glasshouse experiment. Four different NaCl concentrations in the irrigation water, particularly 0.8, 5, 10 and 15 mM, were compared. These were obtained by automatically injecting the required amounts of NaCl to irrigation water containing 0.8 mM NaCl. During the experiment, no drainage solution was discharged. Initially, the electrical conductivity (EC) increased rapidly in the root environment, as indicated by the values measured in the drainage solution. However, 6-7 weeks after recycling initiation the EC of the drainage water approached asymptomatically a maximal level depending on the treatment. The concentration of some macronutrients showed also an increasing tendency with time, but this increase was relatively small and could not account for the observed rise of EC. Hence, this pattern of EC increase was ascribed to accumulation of Na and Cl, which was initially rapid but tended to be minimized as uptake concentrations of Na and Cl were approaching the corresponding concentrations in the irrigation water used to compensate for the transpiration losses. The yield was suppressed by the progressive increase of EC at a rate of 12.3% per unit of EC increase above 3.02 dS m-1. The yield suppression was due to decrease of both the mean fruit weight and the number of fruits per plant. The mean length of the cucumber fruit was also affected by the progressively increasing salinity.
Link (PDF): http://www.actahort.org/members/showpdf?booknrarnr=697_10
Savvas, D., N. Mantzios, P. Barouchas, D. Kyrkas, H.C. Passam, and C. Olympios, 2006. Effects of increasing salinity due to progressive NaCl accumulation in the nutrient solution on French beans grown in a closed hydroponic system. Acta Horticulturae, 747: 531-538
Beans (Phaseolus vulgaris L.) were grown hydroponically using irrigation water with four different NaCl concentrations (0.8, 3.0, 6.0, and 9.0 mM) to compensate for transpiration losses. The experiment was carried out in 12 completely independent closed units, each of which contained two channels accommodating 80 plants per channel, and with 3 replicates per NaCl treatment. The amounts of nutrients supplied to compensate for plant uptake were identical in all experimental units. The different treatments were applied by automatically injecting the calculated amounts of NaCl into the irrigation water, which already contained 0.8 mM NaCl. During the experiment, no drainage solution was discharged. Initially, the recycling of the leachate resulted in a progressive increase in the electrical conductivity (EC) within the root zone (indicated by the values measured in the drainage solution) due principally to NaCl accumulation. However, 60-70 days after the initiation of recycling, the rate of EC increase declined and finally approached zero level, indicating that the EC had asymptomatically reached a maximum, the level of which depended on the NaCl concentration in the irrigation water. The maximum EC level was established as soon as the Na/water and Cl/water uptake ratios (uptake concentrations) had reached the concentration of NaCl in the irrigation water of the particular treatment. The gradual increase of the EC in the root zone imposed a corresponding decrease on water uptake. Due to the progressive increase of the EC, the early fruit yield of bean was hardly affected, but subsequently the yield losses imposed by increasing salinity were considerable. Yield suppression resulted from a decrease in both the mean fruit (pod) weight and the number of pods per plant. The progressive increase in EC did not depress the K, Ca and Mg concentrations in the leaves, but the leaf chlorophyll content was reduced.