Circulating Nutrient Solution Research Articles

Technology development and industrialization trends of circulating nutrient solution supply systems: a review

Hydroponics, a soil-free plant cultivation technique, delivers nutrients directly to roots through a nutrient-rich solution. This method offers advantages over traditional soil-based approaches and has gained attention for its potential to revolutionize controlled agriculture. The review aimed to offer a summary of technological advancements and industrialization patterns in systems supplying circulating nutrient solutions. An intelligent nutrient management system enhances plant growth and productivity. The utilization of a circulating hydroponic cultivation setup can reduce environmental pollution and lower production expenses. As a result, circulating nutrient solution management systems are gaining global popularity, such as in the Netherlands, circular hydroponic cultivation has been advanced to over 95%. A limitation of circulation-type nutrient solution cultivation is the potential transmission and rapid formulation of pathogens during the recycling of discharged nutrient solutions. Addressing this concern, filtration and sterilization processes can offer viable solutions. To accelerate hydroponic farming, an integrated approach could be pursued, strengthen nutrient circulation management technology. This approach could aid in the implementation of such systems in countries like the Republic of Korea, where adoption of circulating hydroponic systems remains under 5%. The trend of technological advancement and industrial growth has been conducted through patent analysis and resources that have subsequently lead the way for the advancement of extensive hydroponic farming establishments. The cyclic hydroponic cultivation in the Republic of Korea was introduced in 2010, and based on the patent information, this endeavor gained momentum from 2020 onward. Furthermore, the analysis underscores the considerable potential of circulating nutrient solution supply systems as viable approaches for promoting sustainable and efficient food production. As a result, forthcoming research and innovation need to be tailored to the local context and prioritize user-centered methodologies, ultimately facilitating the integration and establishment of hydroponic systems in the Republic of Korea.

Obtaining Minitubers by Applying Hydroponic Culture

Hydroponics growing method has proven to be a very successful strategy for the production of pre-base seed potatoes. NIRDPSB Brasov applied this method in 2016, by using two types of culture: with circulating nutrient solution and with static layer of nutrient solution and for both cases the substrate used was perlite. As biological material plantlets of four cultivars (Braşovia, Castrum, Marvis and Sarmis) were used and grown hydroponically in a space “insect-proof” under controlled conditions. The number of minitubers/plant and weight of minitubers/plant were compared for the used cultivars. By using circulating nutrient solution in hydroponic system, Marvis variety (13.80 minitubers/plant) and Castrum variety (11 minitubers/plant) were the best performing of the four cultivars. The hydroponic system with circulating nutrient solution had a positive impact on the mean weight of minitubers/plant, with Marvis variety, recording the highest value (121.6 g).

UVA-LED device to disinfect hydroponic nutrient solution.

The number of plant factories in which crops are cultivated in an artificial environment has been increasing every year. In cultivation techniques involving hydroponics, plants are supplied with a circulating nutrient solution, which can become contaminated by pathogens that can propagate and spread throughout plant factories. Therefore, strategies to disinfect hydroponic nutrient solutions are needed. In this study, we developed a new disinfection device equipped with an ultraviolet A (UVA) light emitting diode (LED) that can be used to disinfect hydroponic nutrient solutions in plant factories. We first evaluated the basic disinfection capability of the device and then estimated its bactericidal effect in a small scale model system. The log survival ratio was related to UVA irradiation fluence and the volume of nutrient solution. From the assay results, we devised a kinetics equation to describe the relationship between nutrient solution volume, log survival ratio, and UVA fluence. Together our results show that UVA irradiation could be used to disinfect hydroponic nutrient solutions, and the derived kinetics equations can be used to determine optimal conditions, such as nutrient solution volume, UVA irradiation, and killing activity, to develop devices that disinfect hydroponic nutrient solutions. J. Med. Invest. 65:171-176, August, 2018.

Bioremediation of creosote contaminated soil in both laboratory and field scale: Investigating the ability of methyl-β-cyclodextrin to enhance biostimulation

We investigated the bioremediation of 16 polycyclic aromatic hydrocarbons (PAH) in historically creosote contaminated soil using both laboratory and field scale experiments. We found that nutrient amendments and circulation of methyl-β-cyclodextrin (CD) solution enhanced soil microbial degradation capacity. In the laboratory experiment, the degradation of lower molecular weight, 2–3 ringed PAHs was achieved already by circulating nutrient solution and the use of CD mainly increased the desorption and removal of larger, 4–5 aromatic ringed PAH compounds. The 1% CD concentration was most feasible for bioremediation as most of the extracted PAH compounds were degraded. In the 5% CD treatment, the PAH desorption from soil was too fast compared to the degradation capacity and 25% of the total PAH amount remained in the circulated solution. Similar lab-scale results have been generated earlier, but very little has been done in full field scale, and none in freezing conditions. Although freezing stopped circulation and degradation completely during the winter, PAH degradation returned during the warm period in the field test. Circulation effectiveness was lower than in the laboratory but the improved nutrient and moisture content seemed to be the main reason for decreasing soil PAH concentrations. It also appeared that PAH extraction yield in chemical analysis was increased by the CD treatment in field conditions and the results of CD-treated and non-treated soil may therefore not be directly comparable. Therefore, a positive effect of CD on PAH degradation velocity could not be statistically confirmed in the field test. Based on our results, we recommend initiating the bioremediation of PAH contaminated soil by enhancing the microbial degradation with nutrient amendments. The CD seems to be useful only at the later stage when it increases the solubilisation of strongly absorbed contaminants to some extent. More investigation is also needed of the CD effect on the PAH yield in the chemical analysis.

MELON PRODUCTION USING FOUR HYDROPONIC SYSTEMS

Melon plants (Cucumis melo L.) were grown using four hydroponic systems of which three used the closed circulating nutrient solution system by deep-flow technique (DFT) but with different designs of growth containers namely, the triangular, double-U and U-shaped PVC containers. The fourth used an open fertigation system with plants grown in polybags containing coconut fiber (coco peat) as the growth medium. Comparisons were made among the systems in terms of nutrient solution electrical conductivity (EC), growth, yield, fruit total soluble solids (TSS) and leaf nutrient composition. Irrigation was applied based on crop transpiration (ET). Electrical conductivity of nutrient solution in triangular containers tended to be higher than the other systems especially during reproductive growth. The EC of nutrients in the solution was lowest with the double-U shaped among the different types of containers. Melon fruit fresh weight was highest with the double-U shaped containers compared to the other systems. However, no significant difference of fresh fruit weight was observed between polybags and triangular containers On the other hand, fruit quality as measured by the TSS (Brix 16) was highest in the U-shaped system compared to the other systems. The N, P, K, Ca and Mg content of leaf tissue of plants in the U-shaped container was also the highest compared to the other systems. During vegetative growth, Leaf Area Index of plants grown in polybags was significantly higher than in the other systems. In conclusion, there is evidence that the superior performance of U and Double-U shaped system was due to better aeration and temperature control.

Oxygen Content and its Diurnal Variation in a New Recirculanting Water Soilless Culture for Horticultural Crops

Based on a new structure for plastic culture channels, a new system for soilless culture called New Growing Systems (NGS) has been developed. It is similar to the nutrient film technique (NFT) but with several potential advantages. Each NGS growing channel has five plastic layers and a large number of holes, there is a dripper every 0.5 m above the first layer of plastic, and each dripper supplies the nutrient solution which flows from the second layer over the others to the end. Three separate greenhouse experiments with tomato, cucumber, and sweet pepper using NGS channels were conducted in Almería (southeastern Spain). The oxygen content in the circulating nutrient solutions was determined at different points and different times along the channels of all crops. Depletion of oxygen content in the nutrient solution was lower than NFT channels. Oxygen content in NGS showed some advantages compared to NFT.

Interaction of Escherichia coli with Growing Salad Spinach Plants

In this study, the interaction of a bioluminescence-labeled Escherichia coli strain with growing spinach plants was assessed. Through bioluminescence profiles, the direct visualization of E. coli growing around the roots of developing seedlings was accomplished. Subsequent in situ glucuronidase(GUS) staining of seedlings confirmed that E. coli had become internalized within root tissue and, to a limited extent, within hypocotyls. When inoculated seeds were sown in soil microcosms and cultivated for 42 days, E. coli was recovered from the external surfaces of spinach roots and leaves as well as from surface-sterilized roots. When 20-day-old spinach seedlings (from uninoculated seeds) were transferred to soil inoculated with E. coli, the bacterium became established on the plant surface, but internalization into the inner root tissue was restricted. However, for seedlings transferred to a hydroponic system containing 102 or 103 CFU of E. coli per ml of the circulating nutrient solution, the bacterium was recovered from surface-sterilized roots, indicating that it had been internalized. Differences between E. coli interactions in the soil and those in the hydroponic system may be attributed to greater accessibility of the roots in the latter model. Alternatively, the presence of a competitive microflora in soil may have restricted root colonization by E. coli. The implications of this study's findings with regard to the microbiological safety of minimally processed vegetables are discussed.

NET MELON CULTIVARS PRODUCTIVITY UNDER DIFFERENT CULTIVATION SYSTEMS, DURING SUMMER AND WINTER

In order to access the effects of cultivation in soil, sand or a commercial substrate on the productivity of Bonus #2 cultivars, ‘Don Carlos’ and ‘Hy Mark’, two experiments were conducted in the greenhouse at FCAV-UNESP, Jaboticabal-SP, Brazil, 21o 15’ 22’’ S, 48o 18’58’’ W, and altitude of 595 m, from November 1999 to April 2000 (summer), and from July to November 2000 (Winter). For cultivation in soil, chemical nutrients were added, and plants were irrigated with drip irrigation. Fertigation with recirculation of the nutrient solution was used on sand; slabs were used on commercial substrate with the fertigation with non circulating nutrient solution. Bonus #2 cultivar yielded the highest production of marketable fruit, but were later in production, while Hy Mark cultivar had early production but a lower number of fruit per plant. The winter planting yielded higher production of marketable fruit while summer plantings yielded lower number of fruit per plant, but with higher average weigh. The combination between cultivation systems and cultivars yielded higher fruit production in winter.

Reduction of fusarium wilt of hydroponically grown basil by Fusarium oxysporum strain CS-20

Basil seedlings were drenched with water or Fusarium oxysporum strain CS-20. The following week, plants were placed in hydroponic troughs with a circulating nutrient solution. Since 2% of the seed was naturally infested with F. oxysporum f. sp. basilici, pathogen inoculum was not applied. After 7 weeks, there were significantly fewer dead stems in plants treated with strain CS-20 than in the control treatment. Laboratory experiments were conducted to determine if a different type of seeding medium could retard dispersal of the pathogen. Oasis is a rigid, open-celled foam used as a medium for seeding and for rooting cuttings. Oasis cubes (cubes physically attached to each other within each tray) and wedges (wedges physically separated within each tray) were seeded with basil. The cube or wedge nearest to the center was inoculated with 10 5 propagules of the pathogen or water. After 1 and 2 weeks, half of the cubes and wedges in each of the three trays were destructively sampled. Different trays were used for the 1- and 2-week samplings. For treatments inoculated with the pathogen, the number of colony forming units (cfu) recovered decreased significantly as the distance from the inoculation site increased. Significantly more cfu were recovered from cubes than wedges when both planting media were inoculated with the pathogen, indicating that the cubes were more conducive to pathogen dispersal than the wedges. In the cubes, the pathogen was recovered 13 cm away from the inoculation site at populations significantly higher than the background levels (up to 10 6 propagules/cube).

DESIGN OF SUSTAINABLE HYDROPONIC SYSTEMS IN RELATION TO ENVIRONMENT-FRIENDLY DISINFECTION METHODS

The last few years Dutch horticulture has changed from a classical production-oriented market to a customer-oriented market. It is no longer the grower who decides about amount and quality of the product. Now, the consumer, and for vegetables more specifically the supermarket prescribes. One of the results is a change from large amounts of a single quality and bulk products to a very segmented presentation of products with different qualities and with added values. In this situation it is important for the grower how the consumer looks at the sustainability of cultivation methods. The enormous boom in system development in the Netherlands has come to a standstill. This enables us to look back to see if there are differences between the former basic assumptions of a “safe, sustainable and competitive” horticultural sector and the commercial application of hydroponic systems. It became clear that many growers choose a certain system for economic reasons. Factors such as low investment, clean restart, labour input are more important than the environment, low annual costs, reuse of materials and substrate. In former years it was said that all circulating nutrient solution had to be disinfected and sterilised to avoid the risk of rapid dispersal of soil-borne pathogens. Now, it is said that the microflora present in the circulating nutrient solution plays an important role in suppressing of root diseases. In that case it becomes more important to eliminate pathogens in such a way that the microflora keeps alive. It has to be determined whether active methods (heat treatment, ozone, UV) can play this role or whether a passive method such as slow sand filtration, which eliminates pathogens group specific, has better prospects. In this paper the commercial application of hydroponic systems will be discussed in relation to the role the natural microflora may have, to suppress soil-borne diseases in the nutrient solution.

PREVENTION OF ROOT DISEASES IN CLOSED SOILLESS GROWING SYSTEMS BY MICROBIAL OPTIMISATION AND SLOW SAND FILTRATION

ISHS International Symposium on Chemical and Non-Chemical Soil and Substrate Disinfectation PREVENTION OF ROOT DISEASES IN CLOSED SOILLESS GROWING SYSTEMS BY MICROBIAL OPTIMISATION AND SLOW SAND FILTRATION

Histology of magnesium-deficient Norway spruce needles influenced by nitrogen source.

Effects of magnesium deficiency and variation in nitrate to ammonium ratio on needle histology and chlorophyll concentration were investigated in current-year and one-year-old needles of clonal Norway spruce trees (Picea abies (L.) Karst.). Six-year-old trees were grown for one year in sand culture with circulating nutrient solutions containing a sufficient (0.2 mM) or a limiting (0.04 mM) concentration of Mg. The nitrogen concentration was not varied (5 mM), but the NO(3) (-)/NH(4) (+)-ratio was adjusted to 0.76 in Mg-sufficient and to 1.86, 0.76 or 0.035 in Mg-limited plants. Visible symptoms of Mg deficiency occurred only in current-year needles, indicating adequate Mg nutrition before the experiment. Under conditions of Mg limitation, chlorophyll and Mg concentrations were lowest in needles of trees supplied with NH(4) (+) as the major nitrogen source and highest in needles of trees supplied with NO(3) (-) as the major nitrogen source. In current-year and one-year-old needles, starch accumulation induced by Mg deficiency was increased when NH(4) (+) was the major nitrogen source. The accumulation of tannin spherules in current-year needles, which occurred in response to Mg deficiency, also increased with decreasing NO(3) (-)/NH(4) (+)-ratios. Deficient Mg supply caused premature aging in tissues of the vascular bundle, as indicated by modifications of the cambium and increased amounts of collapsed sieve cells. The number of collapsed sieve cells was slightly lower in needles grown in a NH(4) (+)-dominated nutrient regime than in needles grown in a NO(3) (-)-dominated nutrient regime. We conclude that was not directly toxic to Norway spruce trees at the applied concentrations. However, effects of Mg deficiency were considerably greater in an NH(4) (+)-dominated nutrient regime than in a NO(3) (-)-dominated nutrient regime.

Influences of different nitrate to ammonium ratios on chlorosis, cation concentrations and the binding forms of Mg and Ca in needles of Mg-deficient Norway spruce

Effects of Mg deficiency and variations of the NO3-/NH4+-ratio on chlorophyll, mineral nutrient concentrations and the binding forms of Mg and Ca were investigated in current-year, one- and two-year-old needles of clonal Norway spruce (Picea abies [L.] Karst.). Six-year-old spruce plants were grown for one year in sand culture with circulating nutrient solutions containing sufficient (0.2 mt M) or limiting (0.04 mt M) concentrations of Mg. The NO3-/NH4+-ratio in the nutrient solutions administered to the experimental trees was adjusted to 0.76 in the Mg-sufficient treatment and to 1.86, 0.76 and 0.035 in Mg-limited treatments. Mg and chlorophyll concentrations, were strongly influenced by the applied nitrogen source in current-year needles and - to a less extent - also in one-year-old needles. NH4+-dominated nutrition resulted in decreased height growth and significantly lower Mg and chloropyhll concentrations in current-year and one-year-old needles compared to NO3--dominated nutrition. Decreases in total Mg were linearly correlated to reductions of water-soluble Mg and water-unsoluble Mg not bound to chlorophyll. Mg bound to chlorophyll, however, was only reduced, when total Mg decreased below a physiological threshold value of 2% of the total nitrogen concentration in the respective needles. Total Ca concentrations in the needles, which were reduced by Mg deficiency especially when nutrition was NH4+-dominated, were strongly correlated to the portion of Ca bound to oxalate. The amount of water-soluble Ca and pectate-bound Ca remained nearly constant, independent from changes of total Ca concentrations. Negative effects of increasing NH4+ supply on concentrations of Mg and other cations in the needles can be attributed to an inhibition of cation uptake induced by ion antagonism and/or reduced root growth.

Study of the microbial dynamics in the root environment of closed, hydroponic cultivation systems for tomato using phospholipid fatty acid profiles.

A more basic understanding of the microbial dynamics of closed, hydroponic cultivation systems is needed. We therefore initiated a study of the microbial community inhabiting the root environment, using phospholipid fatty acid (PLFA) profiles, and started to examine whether changes in the microbial population structure would result from the introduction of selected isolates of plant growth-promoting rhizobacteria (PGPR). Tomato were cultured in deep-flow systems with circulating nutrient solution. Bacteria were sampled from tomato roots at three locations, longitudinally, in the gutters of a control system and in two systems inoculated with PGPR. In the beginning of the gutters the PLFA profiles were similar in all systems, whereas the profiles differed in the gutter ends (following the direction of flow). In the control system, and in a treatment inoculated with two Gram-negative and one Gram-positive PGPR strain, the relative proportion of PLFAs characteristic to Gram-positive bacteria was highest at the end of the gutter. In a treatment inoculated only with a Gram-negative PGPR strain, the relative proportion of PLFAs characteristic of Gram-negative bacteria was highest at the end of the gutter. The results indicate a complex situation with different micro-environments distributed along the root mat. It can also be concluded that PLFA profiles may be useful tools in the study of the microbiology of closed hydroponic plant cultivation systems.

Supported Liquid Membranes for the Extraction of Phenolic Acids from Circulating Nutrient Solutions

Abstract A supported liquid membrane system has been developed for the extraction of phenolic acids for circulating nutrient solutions for tomato culture. A porous PTFE membrane is impregnated with an organic solvent, which thus forms a barrier between two aqueous phases. The analytes are extracted from an aqueous donor solution into the hydrophobic membrane and then back extracted into a second aqueous solution, the acceptor, were the analytes are irreversible trapped. By pumping the donor and keeping the acceptor stagnant, an enrichment of analytes in the acceptor is achieved. The final determination is performed with liquid chromatography and UV-detection utilised with a PRP-1 packed precolumn replacing the injection loop. The stability of five phenolic acids (p-hydroxy benzoic acid, vanillic acid, caffeic acid, p-coumaric acid and ferulic acid) in the nutrient solutions during various storage conditions is reported. High flow rates (up to 6.5 mL/min) are for the first time reported with the SLM-techni...

Magnesium deficiency treatment causes reductions in photosynthesis of well-nourished Norway spruce

In order to investigate effects of magnesium deficiency on Norway spruce [Picea abies (L.) Karst.] photosynthesis, 100 well-nourished 5-year-old spruce trees were grown in sand culture, individually supplied with circulating nutrient solutions. Mineral nutrients were added to the nutrient solutions in optimal quantities and optimal relations to nitrogen. Magnesium was supplied at 0.203, 0.041 and 0.005 mM in order to simulate optimal nutrition, moderate deficiency and severe deficiency. Parameters of photosynthetic gas exchange, chlorophyll, magnesium and starch concentrations were determined in current-year and 1-year-old needles during one growing season. By mid May — 6 months after onset of the Mg deficiency treatments in late autumn — CO2-assimilation rates of 1-year-old needles were significantly decreased independent of the severity of the deficiency treatment, whereas the chlorophyll concentrations did not differ from the controls. The occurrence of yellowing symptoms during July did not further influence the Mg deficiency effect on photosynthesis. In contrast to 1-year-old needles, significant reductions of photosynthesis and chlorophyll in current-year needles were only caused by severely deficient Mg supply. Mg deficiency affected carboxylation efficiency but not light use efficiency. From the accumulation of starch in the needles, up to 30-fold of the controls, the conclusion has been drawn that reactions of CO2-fixation were affected by reduced carbohydrate export. The light-dependent pigment reduction, leading to the typical tipyellowing of needles, clearly reflects a secondary effect of Mg deficiency.

Effect of magnesium‐deficiency on antioxidative systems in needles of Norway spruce [Picea abies (L.) Karst.] grown with different ratios of nitrate and ammonium as nitrogen sources

summaryThe effect of magnesium deficiency and variations of the ammonium to nitrate ratio on chlorophyll, soluble protein and antioxidative systems was investigated in current year's needles of clonal spruce trees [Picea abies (L.) Karst.]. The trees were grown for 1 yr in sand culture with circulating nutrient solutions containing sufficient (0.2 mM) or limiting (0.041 mM) concentrations of Mg. The nitrogen concentration of the nutrient solutions was not varied (5 mM) but the NO3−/NH4+‐ratio was adjusted TO 0.76 in Mg‐sufficient and to 1.86, 0.76 and 0.035 in Mg‐limited plants, Under Mg‐limitation, the chlorophyll, soluble protein and Mg‐contem were lowest in needles of trees supplied with NH4+ and highest in trees supplied with NO4− as major N‐source. Apoplastic peroxidase activities were not affected by changes in nutrition. In total needle extracts, NADH oxidase, ascorbate peroxidase, mimodehydroascorbate reductase, glutatkione reductase and asoorbate content were not, or only little, affected by changes in nutrition, except for trees grown with the highest N4+‐concentrations. Glutathtone content and guaiacol peroxidase were increased in Mg‐deficient needles. Superoxide dismutase activity was decreased in Mg‐limited needles of trees grown with N4+ and increased in needles of trees grown with NO3− as a major N‐source, Except for superoxide dismutase, the activities of antioxidant enzymes and substrates were not correlated with the decree of needle chlorosis. Superoxide dismurase activity was low compared to enzymatic activities involved in H2O2 detoxification. Supposing that the needles suffered from enhanced oxidative stress, these results suggest that scavenging of O2− was a limiting factor in stress compensation rather than the detoxification of H2O2.

Aluminium avoidance by Mucuna pruriens

The hypothesis was tested that the avoidance of acid subsoil by the velvet bean Mucuna pruriens is based on a mechanism acting on the whole root system rather than on individual roots. In a split‐root experiment with circulating nutrient solution the growth of plants with Al‐containing (+/+) or Al‐free (0/0) solution on both sides of the root system was compared with that of plants which had a choice (0/+). Two levels of Al (110 and 185 μM) were tested at two levels of Ca (50 and 1250 μM). In the 185 μM Al treatment the concentration of monomeric Al varied between 53 μM, directly after refreshing the solution, and 5 μM at harvest time.An external Al concentration of 110 μM had no effect on shoot and root dry weight, while 185 μM Al applied to both sides of the root system (+/+) increased root dry weight and reduced shoot dry weight and shoot/root ratio, compared with the 0/0 control. Application of 185 μM Al to half of the roots, ied to a significant shift in root growth in favour of the control side; this response is described here as Al avoidance. On the basis of total root length, root dry weight and root surface area, the ratio of 0/+ roots was 3.1, 2.8 and 2.4, respectively.Al avoidance at 185 μM Al was confirmed in another experiment, in which root response was measured to a local P source, supplied in a third compartment containing only KH2PO4. A significant increase in root length and dry weight in this compartment was observed, when other roots of the same plant were growing in the presence of Al. This result indicates that Al avoidance by Mucuna roots is related to P preference.

Cultural practices and integrated pest management (IPM) in glasshouses

Sufficient hygiene is an important instrument in preventing infestations of glasshouse crops. Since chemical soil sterilization is more and more restricted, soil-steaming and closed growing systems are coming more and more in use. With closed systems, the question of disinfecting the circulating nutrient solution arises. Screens of different mesh are being tested for the exclusion of pests from glasshouse crops. More and more attention is being paid to the influence of the glasshouse microclimate on the occurrence and spread of pests. Various aspects are discussed in relation to temperature, humidity, leaf wetness, radiation, etc.

Drainwater filtration for the control of nematodes in hydroponic-type systems

Ornamental pot plants grown on hydroponic-type systems may be infected by nematodes distributed by the circulating nutrient solution. Laboratory and practical experiments demonstrate the usefulness of filtration techniques for effective nematode control. A filter unit was built in which the drainwater was caught in a sedimentation reservoir from which it was pumped (1000 1 h −1) into a second tank, passing through a series of four filters comprising a gauze cartridge (150 μm) and three polyester felt filter bags (80, 1 and 1 μm). All the plant-parasitic nematodes were retained.