Recycled Nutrient Solution Research Articles

Comparisons of Ion Balance, Fruit Yield, Water, and Fertilizer Use Efficiencies in Open and Closed Soilless Culture of Paprika (Capsicum annuum L.)

Although closed soilless culture is useful for saving water and fertilizers with minimizing environmental pollution, adequate management of nutrient solutions is still not stabilized in greenhouse cultivation. In order to investigate the problems occurred in closed soilless culture of Paprika (Capsicum annuum L., cv. Fiesta), we compared ion balance, fruit yield, and the water and fertilizer use efficiencies in the closed system with those in the open system. The plants were grown in rockwool culture with a nutrient solution of EC 2.5 dS·m -1 . After 4 weeks of treatment, individual ratio of NO₃ - , K + , Ca 2+ , and Mg 2+ to total ion concentrations (meq쩖-1) decreased from the initial value, especially the biggest decrement was observed in K + , and on the other hand, SO₄ 2- , Cl - , and Na + were accumulated in the closed system. Yields after four-time harvests were 19% higher in the open system than in the closed system. Total volume of water used per unit area (㎡) in the open system was 20% higher, but the total water use per fruit was not significantly different between the two systems, while t total fertilizer use per fruit was 78% higher in the closed system. Amount of marketable fruits was not significantly different between the two systems. We concluded that the increase in K + supply and the replenishment of recycled nutrient solution every four weeks were required for preventing the imbalance or depletion of nutrients in the close soilless culture of paprika plants to get more balanced nutrient composition during whole cultivation period.

Uptake of Mn and Zn by Cucumber Grown in Closed Hydroponic Systems as Influenced by the Mn and Zn Concentrations in the Supplied Nutrient Solution

The objective of the present experiment was to estimate the uptake of manganese (Mn) and zinc (Zn) by cucumber in closed hydroponic systems at different Mn and Zn concentrations in the recycled nutrient solution under Mediterranean climatic conditions. The obtained data might be used to manage Mn and Zn supply in closed hydroponic crops of cucumber grown in Mediterranean greenhouses and avoid their accumulation to toxic levels. Four Mn levels (10, 40, 80, 120 μM) at a standard Zn concentration (6 μM) and four Zn levels (6, 20, 40, 60 μM) at a standard Mn concentration (10 μM) in the solution supplied to compensate for nutrient and water uptake by plants were applied as experimental treatments. The actual uptake concentrations of Mn and Zn were estimated by applying two different methods. The first method was based on the removal of Mn, Zn, and water from the recycling nutrient solution, whereas the second method was based on the total quantities of Mn and Zn that were recovered in plant biomass in combination with the total water uptake. Both methods gave similar uptake concentrations for Mn in the low-Mn supply level and Zn in all Zn levels. However, in the three higher Mn supply levels, the values estimated on the basis of nutrient removal from the recirculating nutrient solution were significantly higher than those found by measuring the total Mn content in plant biomass. These discrepancies in the three high-Mn treatments were possibly caused by partial immobilization of Mn by oxidizing bacteria in the nutrient solution.

Effects of boron on leaf chlorophyll fluorescence of greenhouse tomato grown with saline water

Imaging chlorophyll fluorescence was used to study the response of greenhouse tomato grown in soilless culture to NaCl and B concentration in the irrigation water. The plants were grown in perlite with recycling nutrient solution, which was prepared with negligible concentration or 550 mg L −1 of NaCl, and 0.5 or 2.0 mg L −1 of B in the irrigation water. High B concentration resulted in evident necrosis of leaf margins. At high NaCl concentration the recycling nutrient solution was replaced more frequently than at low salinity and this resulted in lower B concentration in the root zone, thus limiting the incidence of necrotic areas in the leaves. Indeed, the severity of leaf damage was linearly related to the mean B concentration in the recycling water. In all treatments we observed a strong difference in B concentrations between marginal and central areas, the latter remaining green and viable even in condition of severe B toxicity, as indicated by the determination of chlorophyll fluorescence. A reduction of the photosynthetic activity was observed in the symptomatic areas of the leaves on the plants grown at high B concentration in the root zone as a result of reduced dissipation of the excess of excitation energy at PSII level.

Proton NMR quantitative profiling for quality assessment of greenhouse-grown tomato fruit

Tomato is an essential crop in terms of economic importance and nutritional quality. In France, the third most important region for tomato (Solanum lycopersicum L.) production is Aquitaine where the major part of production is now grown soilless under greenhouse conditions with harvest from March to November. Tomato fruit quality at harvest is a direct function of its metabolite content at that time. The aim of this work was to use a global approach to characterize changes in the fruit organoleptic quality at harvest under commercial culture conditions during an entire season for two varieties and two different fertilization practices (with or without recycling of the nutrient solution) for one variety. Absolute quantification data of 32 major compounds in fruit without seeds were obtained through untargeted (proton nuclear magnetic resonance, 1H-NMR) quantitative profiling. These data were complemented by colorimetric analysis of ascorbate and total phenolics. They were analyzed with chemometric approaches. Principal component analysis (PCA) or partial least square analyses (PLS) revealed more discriminant metabolites for season than for variety and showed that nutrient solution recycling had very little effect on fruit composition. These tendencies were confirmed with univariate analyses. 1H-NMR profiling complemented with colorimetric analyses therefore provided a diagnostic tool to follow the changes in organoleptic and nutritional quality of tomato. In addition the quantitative information generated will help to increase our knowledge on the mechanisms of plant response to environmental modifications.

THE INFLUENCE OF IRRIGATION METHOD ON POT GERANIUM (PELARGONIUM PELTATUM L.) GROWN WITH SALINE WATER

ISHS International Symposium on Strategies Towards Sustainability of Protected Cultivation in Mild Winter Climate THE INFLUENCE OF IRRIGATION METHOD ON POT GERANIUM (PELARGONIUM PELTATUM L.) GROWN WITH SALINE WATER

Molecular Identification of Microbial Communities in the Recycled Nutrient Solution of a Tomato Glasshouse Soil-Less Culture

This study aimed to assess microbial community diversity in recycled nutrient solutions used in soil-less glass- house cultivation of tomato. One hundred bacterial strains, twenty oomycetes and 6 fungi were isolated and identified through genomic DNA isolation, PCR amplification of the ribosomal DNA region and database interrogations. Similari- ties of ITS regions with known species ranged from 95% to 100%. This artificial ecosystem was shown to be microbio- logically diverse, since recovered isolate were close to 35 bacterial species, 11 oomycete species and 3 fungal species. Bacteria belonged almost exclusively to � -Proteobacteria and Firmicutes, with most represented genera being Bacillus, Acinetobacter, Klebsiella and Serratia. A few bacterial sequences grouped with clones similar to plant and human patho- gens, while other isolates could be protective bacteria such as Pseudomonas fluorescens. Oomycetes isolated mostly be- longed to the genus Pythium (19 isolates) and were phylogenetically related to common cosmopolitan soil inhabitants or phytopathogenic Pythium species. The six fungal isolates were in 2 genera, Rhizopus and Caesia; Rhizopus isolates were closely related to the post harvest pathogen Rhizopus stolonifer. This original work adds to the efforts of assessing micro- organism diversity in recycled nutrient solutions commonly used in glasshouse vegetable production; microbial diversity was high and included potential plant pathogens. This study demonstrated the existence of a wide cultivable microbial community in the nutrient solution before recycling and recirculation and supported the necessity for disinfecting nutrient solutions used in soil-less cultivation systems, during the recycling process, in order to ensure crop sanitation and avoid- ing plant disease spreading.

Detoxification of Phytotoxic Compounds by TiO2Photocatalysis in a Recycling Hydroponic Cultivation System of Asparagus

TiO 2 photocatalytic decomposition and detoxification of phytotoxic compounds released by the roots of asparagus ( Asparagus officinalis L.) were investigated from the viewpoint of conservation-oriented cultivation. The phytotoxically active fraction was extracted either from dried asparagus roots or from the recycled nutrient solution of an asparagus hydroponic cultivation system. We found that the phytotoxic activity gradually decreased in the fraction with TiO 2 powder under irradiation with ultraviolet (UV) light at an intensity of 1.0 mW/cm (2). The growth of asparagus plants under actual cultivation conditions was also investigated by comparing asparagus grown in a hydroponic system where recycled waste nutrient solution was photocatalytically treated with solar light and a system with untreated recycled waste nutrient solution. The results showed, as measured by growth indices such as stem length and stem thickness, that asparagus growth in the photocatalytically treated system was superior to the untreated one. Furthermore, the yield of asparagus spears was 1.6-fold greater in the photocatalytically treated system, demonstrating the detoxification effect on the phytotoxic compounds and also the killing effect on pathogenic microorganisms.

Selective Enhancement of the Fluorescent Pseudomonad Population After Amending the Recirculating Nutrient Solution of Hydroponically Grown Plants with a Nitrogen Stabilizer

Fluorescent pseudomonads have been associated, via diverse mechanisms, with suppression of root disease caused by numerous fungal and fungal-like pathogens. However, inconsistent performance in disease abatement, after their employment, has been a problem. This has been attributed, in part, to the inability of the biocontrol bacterium to maintain a critical threshold population necessary for sustained biocontrol activity. Our results indicate that a nitrogen stabilizer (N-Serve, Dow Agrosciences) selectively and significantly enhanced, by two to three orders of magnitude, the resident population of fluorescent pseudomonads in the amended (i.e., 25 microg ml(-1) nitrapyrin, the active ingredient) and recycled nutrient solution used in the cultivation of hydroponically grown gerbera and pepper plants. Pseudomonas putida was confirmed as the predominant bacterium selectively enhanced. Terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rDNA suggested that N-Serve selectively increased P. putida and reduced bacterial diversity 72 h after application. In vitro tests revealed that the observed population increases of fluorescent pseudomonads were preceded by an early growth suppression of indigenous aerobic heterotrophic bacteria (AHB) population. Interestingly, the fluorescent pseudomonad population did not undergo this decrease, as shown in competition assays. Xylene and 1,2,4-trimethylbenzene (i.e., the inert ingredients in N-Serve) were responsible for a significant percentage of the fluorescent pseudomonad population increase. Furthermore, those increases were significantly higher when the active ingredient (i.e., nitrapyrin) and the inert ingredients were combined, which suggests a synergistic response. P. putida strains were screened for the ability to produce antifungal compounds and for the antifungal activity against Pythium aphanidermatum and Phytophthora capsici. The results of this study suggest the presence of diverse mechanisms with disease-suppressing potential. This study demonstrates the possibility of using a specific substrate to selectively enhance and maintain desired populations of a natural-occurring bacterium such as P. putida, a trait considered to have great potential in biocontrol applications for plant protection.

Modelling Na and Cl concentrations in the recycling nutrient solution of a closed-cycle pepper cultivation

A mass balance model relating the concentrations of Na or Cl in the recycled nutrient solution to the cumulative uptake of water by the plants was calibrated and validated in greenhouse sweet pepper crops grown in closed-cycle cultivation systems. The results indicated that the model allows for simulation of the courses of Na and Cl accumulation in closed-cycle cultivations of pepper, provided that the fluctuations in the volume of drainage solution and the moisture status of the substrate during the cropping period are small. Furthermore, the model predicts a delay in the process of salt accumulation in closed-cycle hydroponic systems when the drainage percentage is relatively high due to enhanced irrigation frequency, in compassion with standard irrigation frequency. The proposed model may be incorporated into intelligent automation systems to automatically adjust the target total salt concentration in the outgoing irrigation solution to levels allowing for a constant nutrient supply, despite the Na and Cl accumulation in the recycled leachate. As a result, the entire amount of drainage solution can be recycled without risking depletion of essential nutrients in the root zone.

Interactions between salinity and irrigation frequency in greenhouse pepper grown in closed-cycle hydroponic systems

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 mol m −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.

Assessment of the Differences in the Phenolic Composition of Five Strawberry Cultivars (Fragaria × ananassa Duch.) Grown in Two Different Soilless Systems

The phenolics from different strawberry cultivars (Aromas, Camarosa, Diamante, Medina, and Ventana) cultivated in two different soilless systems (with and without recycling nutrient solution) were quantified to assess differences in their profiles as a function of both the variety and the cultivation system. Considering groups of phenols, it was found that either anthocyanins (including pelargonidin-3-glucoside, cyanidin-3-glucoside, pelargonidin-3-rutinoside, pelargonidin-3-acetylglucoside, and two unidentified pelargonidin derivatives) or phenolic acids (including caffeic, ferulic, p-coumaric, p-hydroxybenzoic, and ellagic acid) were quantitatively more important than those of flavonols (quercetin and kaempferol); the ranges of values were 78.81-198.88, 49.77-128.37, and 12.85-43.04 microg/g, respectively. Considering individual compounds and after applying relevant pattern recognition techniques, it was concluded that the contents of cyanidin-3-glucoside, pelargonidin-3-rutinoside, p-coumaric acid, and pelargonidin-3-glucoside were the most appropriate variables to discriminate among varieties, whereas those of p-hydroxybenzoic acid and pelargonidin-derivative 1 were the most appropriate to discriminate between cultivation systems. The first factor of PCA was mainly linked to anthocyanins and quercetin, whereas the second principal component (PC) was related to kaempferol and p-coumaric acid.

An aggregated model for water requirements of greenhouse tomato grown in closed rockwool culture with saline water

The paper reports an aggregated model for the water requirements ( W) of greenhouse tomato grown in spring or summer–autumn season in closed (recycling nutrient solution) rockwool culture. A series of experiments were conducted between 2000 and 2003. In each experiment, two different nutrient solution treatments were established in a randomized block design, with three replicates. The nutrient solutions differed only for the concentration of NaCl and the electrical conductivity (EC), which were, respectively, 10 mol m −3 and 3.0 dS m −1 in T10 treatment, and 20 mol m −3 and 3.9 dS m −1 in T20 treatment. Fruit yield was 10.1 ± 0.3 and 9.6 ± 0.2 kg m −2 in T10 and T20 treatments, respectively, and the difference was not significant. Two diverse sub-models were developed, for the daily crop water uptake ( W U) and for the leaching requirement (LR) in dependence of a maximum tolerable sodium (Na +) concentration in the recycling nutrient solution. W U was simulated using a simple regression model, which considered the radiation actually intercepted by the crop. The determination coefficient for the linear regression between predictions ( P) and measurements ( M) of daily W U was 0.853 ( n = 581), with the slope (0.963) and the intercept (−0.053) of the linear regression not significantly different, respectively, from 1 and 0. There was a good agreement between P and M values of W U, with a mean deviation between P and M of 2 ± 10%. The modelling of LR was less satisfactory, especially in spring crops; the average value for P and M values of LR was 0.30 and 0.28, respectively. The P– M residual averaged 11 ± 25% for LR and 13 ± 26% for the volume of drainage water or runoff ( W R). Nevertheless, the aggregated model accounted well for W with an average deviation of 4 ± 11% between P and M. The sensitivity analysis showed the great influence of radiation on W and suggested that the quality of irrigation water (namely, NaCl concentration) is more relevant for crop water use efficiency than any other factor considered by the LR model, including the affinity of the plant for the salts contained in the nutrient solution.

COMPARISON OF OPEN AND RECYCLING SYSTEMS FOR ION ACCUMULATION OF SUBSTRATE, NUTRIENT UPTAKE AND WATER AND WATER USE OF TOMATO PLANTS

COMPARISON OF OPEN AND RECYCLING SYSTEMS FOR ION ACCUMULATION OF SUBSTRATE, NUTRIENT UPTAKE AND WATER AND WATER USE OF TOMATO PLANTS

RESPONSE OF ASIATIC LILY TO NUTRIENT SOLUTION RECYCLING IN A CLOSED SOILLESS CULTURE

Response of asiatic lily to nutrient solution recycling in a closed soilless culture system

A SYSTEM FOR FERTIGATION MANAGEMENT IN CLOSED-LOOP SOILLESS CULTURE OF TOMATO

Protected cultivation of tomato is specific to the production for fresh market. In Italy, most greenhouse growers apply fertigation with free drainage (open-loop system) but recent legislation concerning environmental pollution from point source is forcing them to introduce new management approaches, namely the recirculation of drain water (closed-loop system). To support the growers in selecting low impact growing systems and in reducing water use a specific support system (SGx) is under construction. SGx integrates three main simulation models of plant growth and transpiration as well as the nutrient concentration in fertigation water. The system can run both in real time, using meteorological and water consumption data automatically collected by in situ sensors, and off-line using data sets archived in the database. In real time modality, the system follows plant growth and the modification of recycling nutrient solution and advices growers about to the most effective practices in term of crop growth and water and nutrient use. The off-line modality allows different fertigation strategies to be evaluated from the viewpoints of economics and environmental impact.

Fate of metalaxyl applied in nutrient solution to gerbera (Gerbera jamesonii) grown in a ‘closed’ hydroponic system

SummaryThe application of fungicides via the recycled nutrient solution in ‘closed’ hydroponic systems may restrict the leaching of residues into groundwater. To assess the possibility of applying selected fungicides via the recycled nutrient solution to flower crops grown in ‘closed’ hydroponic systems, the widely-used fungicide metalaxyl was applied to gerbera (Gerbera jamesonii) at two different doses (112.5 and 225 mg l–1) using this method. The experiment was conducted in a glasshouse using pumice (0–5 mm) as the substrate. The fate of the metalaxyl, which was added to the nutrient solution was traced in the plants and the environment by regularly collecting samples of irrigation solution, drainage water, pumice, roots, leaves, and flowers over a period of 121 d and analysing them by gas chromatography. Metalaxyl residues in leaves were also studied over a 50 d summer period, 7 months later. Metalaxyl concentrations were relatively high in both drainage and irrigation solutions over the first 5 d following its application, but dropped markedly on day 17. Thereafter, the metalaxyl level declined slowly to a mean value of 0.02 mg l–1 on day 121, without any significant difference between the two doses originally applied. The estimated half-life of the metalaxyl was 6.5 and 5.4 d at the low and high dose, respectively. Leaf concentrations of metalaxyl increased gradually during the first 5 d following application, and remained almost constant up to day 17. Thereafter, leaf concentrations declined progressively to 0.6 mg kg–1 (fresh weight) by day 121, without significant differences between treatments. This response, independent of application dose, implies that even lower doses of metalaxyl may be applied via the nutrient solution in ‘closed’ hydroponics. The concentration of metalaxyl in roots reached a peak earlier than in leaves. In the 50 d, summer experiment, the highest concentration of metalaxyl in leaves was found 6 d after application, followed by a rapid decrease. Theses results indicate that application of metalaxyl via the recycled nutrient solution in a ‘closed’ hydroponic system provides effective, high concentrations of the fungicide in roots and leaves, which are maintained for a long period after application.

Influence of nitrogen availability on shoot development in young peach trees [ Prunus persica (L.) Batsch

It is commonly stated that nitrogen (N) influences biomass accumulation in plants. For trees, however, a precise characterisation of shoot response to N and its impact on architecture is lacking. We attempted to study on the phytomer scale the effects of N limitation on shoot growth components, i.e. leaf emergence rate, final internode length and branching on the main and secondary axes of 1-year-old peach trees [Prunus persica (L.) Batsch]. Trees were grown on recycled nutrient solutions in which N concentration was restored once a week. We used two hydroponic set-ups in which weekly N availability, i.e. amount of N per tree, differed being either low (N1) or high (N2). Net N availability was defined weekly as the relative amount of N remaining in each set-up before solution replenishment. It declined with time and three periods of contrasting net N availability were identified. During these periods, leaf emergence rate and final internode length were similar on the main axis of N1 and N2 trees, so too was the distribution of secondary axes along the main axis. Secondary axes responded to N limitation by decreasing their growth components according to their position along the main axis. Differences were most important for basal secondary axes. Leaf emergence rate and final internode length responded similarly to N availability depending on axis order and position in the tree. It was concluded that N availability, particularly during the period of maximum growth of axes, influenced the shoot growth components and thus tree architecture.

Response of hydroponically grown gerbera to nutrient solution recycling and different nutrient cation ratios

The effects of recycling the drainage solution by adding nutrients to replenish it at three different K:(K+Ca+Mg) ratios (0.40, 0.48, 0.56, equivalent basis) on yield, flower quality and nutritional status of soilless-grown gerbera were investigated. The recycling treatments were compared also to a control with free drainage and a standard K:(K+Ca+Mg) equivalent ratio of 0.40 in the irrigation solution. The ratios between NH 4 and total N, Ca and Mg, macronutrient anions, and micronutrients, were identical in all treatments when injecting concentrated solutions of fertilizers to prepare fresh nutrient solution, and similar to standard recommendations for open systems, regardless of recycling or not. Furthermore, the target electrical conductivity and pH in the irrigation solution were identical in all treatments. When the drainage solution was recycled, the highest yield was obtained with the highest K:(K+Ca+Mg) injection ratio. However, both the number of flowers per plant and the flower stem length were significantly lower in all recycling treatments compared to those obtained when the effluents were discharged. This was attributed to a profound decline of the NH 4 concentration in the drainage solution and, thus, also in the irrigation solutions prepared by reusing it, which resulted in increased pH in the root environment and restricted supply of Mn to the plants. In addition to Mn, the leaf P and Fe concentrations were also reduced by the increased pH in the root zone when recycling was applied. Hence, to prevent nutrient imbalances in closed hydroponic systems, it is suggested to supply potassium and nitrogen at higher K:(K+Ca+Mg) and NH 4/total-N ratios than those recommended for open systems.

Availability of iron in hydroponic nutrient solutions for rose crops

SummaryThis study investigated the effect of light and agitation on the availability of iron in hydroponic nutrient solutions.In recycled hydroponic nutrient solutions used for the cultivation of roses, iron is added usually in the form of chelatefertilizers, such as Fe-EDDHA. In practice, the concentration of iron in the nutrient solution in those systems reaches lowcritical levels very rapidly (in less than 2.d). Fe-chelates are unstable in light and can form soluble or insoluble precipitates. Iron contained in soluble precipitates can be recovered in the solution by agitation. In contrast, iron containedin insoluble precipitates cannot be recovered. The tank of the closed-loop fertigation system used to grow a rose cropwas filled with fresh nutrient solution every 10.d. Immediately after preparing each solution, four 1.l plastic bottles were filled with the solution and kept in light or in the dark (two bottles of each), at the same temperature. For the next 10.dthe concentration of iron in the tank was measured every 2.d, without any agitation before measurement, and in the bottlesbefore and after agitation. Incident solar radiation in the greenhouse was recorded continuously. It was observed that absorption by the plants and light exposure did not affect the availability of iron in the nutrient solution. Ion concentration was not different between the samples kept in light and those kept in the dark. Agitation increased the quantity of iron available compared with the non-agitated solution. The increase was greater in the solution kept in light (+59%) than inthe solution kept in the dark (+35%). The pattern of iron concentration in the recycled nutrient solution was similar to that measured without agitation in the solution exposed to light. It was concluded that in a closed hydroponics systems, agitation is very useful for keeping the concentration of available iron at acceptable levels for longer periods and thus minimizing further addition of iron, while exposure to light does not affect Fe availability.

Influence of Sub- Versus Top-irrigation and Surfactants in a Recirculating System on Disease Incidence Caused by Phytophthora spp. in Potted Pepper Plants

Zoospores of Phytophthora capsici spread from inoculated source plants to healthy potted pepper plants located on separate ebb-and-flow benches when the recycled nutrient solution originated from a common reservoir. Amending the recirculating nutrient solution with a surfactant, which selectively kills zoospores, resulted in 100% control of the spread of the pathogen in an ebb-and-flow and a top-irrigated cultural system. Without a surfactant in the recirculating nutrient solution, all plants in an ebb-and-flow cultural system died within 6 weeks. In contrast, all plants in a top-irrigated cultural system died within 2 weeks after inoculation of source plants. These results suggest that the use of recycled irrigation water in an ebb-and-flow cultural system is less conducive to pathogen spread than its use in a top-irrigated cultural system, but may still serve as efficient means of inoculum movement in the absence of control measures.