Soilless Container Research Articles

Effects of Vermicompost Substrates and Coconut Fibers Used against the Background of Various Biofertilizers on the Yields of Cucumis melo L. and Solanum lycopersicum L.

Vermicompost has been promoted as a viable substrate component owing to its physicochemical properties, nutrient richness, and status as an excellent soil improver. It is considered the best organic fertilizer and is more eco-friendly than chemical fertilizers. Plant-growth-promoting microorganisms (PGPMs) are defined as plant biofertilizers that improve nutritional efficiency—that is, they transform nutrients within substrates from organic to inorganic forms, making them available for plants. The main objective of this research study is to evaluate the effects of the application of three PGPM microbial consortia on different mixtures of organic substrates based on vermicompost (V) and coconut fiber (CF) on two different horticultural crops. We performed a yield analysis and drainage nutrient tests and determined the plant nutritional status and enzymatic activity in organic substrates based on the two crops, Cucumis melo L. and Solanum lycopersicum L. A multivariate analysis of variance and principal component analysis was conducted using substrate types and PGPMs as factors. Differences (p < 0.05) in yield, dehydrogenase activity, the nutrient concentrations in a petiole sap, and drainage were observed at 30, 60, 75, and 90 days after transplant. PGPMs such as Trichoderma sp. and plant-growth-promoting rhizobacteria (PGPR) in organic substrates (40V + 60CF) can significantly improve the nutritional status of plants for use in organic soilless container agriculture. Biofertilization with PGPMs and suitable mixtures of organic substrates together with aqueous extracts (tea) of vermicompost, as nutrient solutions applied by fertigation, has allowed us to achieve an adequate level of production through environmentally friendly techniques. The results obtained allowed us to affirm that it was possible to replace conventional fertilization using no chemical products and ensure adequate crop nutrition by supplying main macronutrients with organic sources and biofertilizers.

Water and Air Relations in Propagation Substrates

Greenhouse propagation of unrooted plant cuttings is characterized by short container cell height and high irrigation frequency. These conditions can result in high moisture level and low air content in soilless container substrates (“substrates”), causing delayed growth of adventitious roots and favoring root disease. The objective of this study was to quantify and compare substrate water and air relations for three propagation substrates (peat, rockwool, and phenolic foam) that varied widely in physical characteristics using four methods: 1) evaporation method with a tensiometer, 2) frozen column method, 3) gravimetric analysis, and 4) X-ray computed tomography (CT) analysis. Moisture retention curves based on evaporation (1) and the frozen column (2) resulted in differences for peat, but similar curves for rockwool and foam. The frozen column method was simple and low cost, but was constrained by column height for peat, which had a higher water potential compared with the other two substrates. Substrate porosity analysis at container capacity by gravimetric or CT methods were similar for volumetric water and air content (VWC and VAC) in rockwool and foam, but differed for peat for VWC and VAC. Gravimetric analysis was simple, rapid, and low cost for whole-cell analysis, but CT further quantified spatial water and air relations within the cell and allowed visualization of complex water and air relations in an image. All substrates had high water content at container capacity ranging from 67% to 91% VWC with 5% to 11% VAC in the short propagation cells, emphasizing the need for careful irrigation management.

Use of Dry Dairy Manure Pellets as Nutrient Source for Tomato (Solanum lycopersicum var. cerasiforme) Growth in Soilless Media

A sustainable dairy manure amendment for soilless crop growth systems was evaluated for its ability to provide nutrients and serve as a major component of the growing media. After manure liquid/solid separation, the solids stream containing organic N and P was pelletized and used as a nutrient source for cherry tomato (Solanum lycopersicum var. cerasiforme) culture in soilless media. The pellets are low in moisture, odor, and pathogens, and they can be hauled at lower cost over longer distances and more easily stored than raw or composted manure. Manure pellet additions to soilless media were evaluated at 0%, 2.5%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, and 50% by volume. Manure pellets had a total N content of 3.7%. Fruit size, ripeness, and biomass, plant height, nutrients value in tissue/pellets/media, and time to complete growth cycle were analyzed. Overall, manure pellet treatments improved plant height and growth rate compared to the negative control, especially when pellets were 15% to 50% of the soilless media. This indicates that the nutrients in the manure were being mineralized, and plants were able to utilize the manure-based nutrients for growth. Leaf tissue nutrient analysis revealed that N, K, Zn, and Fe in leaf tissue were not at sufficiency levels at any level of manure pellet addition. Phosphorus and Cu reached sufficiency levels with 10% or greater manure pellet additions. Calcium, Mg, S, Mn, and B were sufficient in all plants, regardless of fertilizer or manure pellet treatment. Manure pellets demonstrate the potential to be used as a substrate and partial growth medium to reduce synthetic fertilizer use for more sustainable soilless container culture.

High Frequency of Plant Regeneration through Adventitious Shoots Proliferation from Leaf Explant of Patchouli–Pogostemon cablin (Blanco) Benth

Plant regeneration potential through adventitious shoots proliferation was studied from leaf explant of evergreen perennial aromatic herb, patchouli plant, or Pogostemon cablin. Leaf explant showed differentiation of embryogenic callus on Murashige and Skoog’s medium (MS) supplemented with 2,4-D 0.5 mg L-1, 3% sucrose and 0.9% agar. Embryogenic callus was further transfer to same medium with BA 0.5 mg L-1 produced somatic embryos and adventitious shoots having dark green colour after four weeks. The maximum range of embryogenesis frequency was 89%, depending on the BAP concentration in combination with 2,4-D. The best response was observed on MS medium containing 0.5 mg L-1 BAP along with 0.5 mg L-1 2,4-D. The embryos or adventitious shoots matured and developed on fresh MS medium with growth regulators. Maximum numbers of 74 adventitious shoots germination were observed and developed further for root induction on the medium containing 0.5 mg/l BAP and 0.5 mg/l NAA after six weeks of culture. Regenerated shoots were separated and rooted on same half strength MS medium supplemented with 1.0 mg/l of NAA alone for three weeks. Approximately 30-105 plantlets were regenerated from each leaf explant. Well-regenerated plants grew vigorously after transplanting to a soil-less container in shade house.

Assessment of suitability and suppressiveness of on-farm green compost as a substitute of peat in the production of lavender plants

ABSTRACTSuppression of root rot diseases of ornamental plants is a potential benefit of formulating soilless container media with compost. A green compost (green nursery compost, GNC), obtained by a circular-economy approach from residues of pruning of woody plants and grass clippings during the nursery activities was analysed for its suppressiveness of root rot diseases using lavender. To this end, a bioassay was develop by formulating potting mixes containing GNC with two rates of peat substitution (25% and 50%) and infested with the root rot pathogens Sclerotinia sclerotiorum, Rhizoctonia solani and Phytophthora nicotianae. Contrasting results were obtained by using both substrates with a significant reduction of root rot by S. sclerotiorum, no effect on the containment of that by P. nicotianae, and an increase of symptoms caused by R. solani. The specific suppressiveness observed may be attributed to the colonisation of compost by specific groups of antagonistic microorganisms. This hypothesis was investigated by the analysis of culturable fungal community, which resulted in the isolation of Trichoderma harzianum and T. atroviride as preponderant fungal species. Trichoderma representative isolates exerted in vitro antagonistic activities against the target pathogens with varying efficiencies indicating the employment of multiple complementary mechanisms, which may have contributed to the observed specific suppressiveness. Both substrates containing GNC resulted suitable for nursery cultivation of lavender, showing a growth performance similar to that obtained with peat-based substrate. Present results indicate that on-farm compost is a suitable component of mixed-peat substrates capable to support plant growth and provide specific disease suppression.

Use of Ground Wheat Straw in Container Nursery Substrates to Overwinter Daylily Divisions2

Wheat (Triticum sp.) straw is being evaluated as a potential component in soilless container mixes either alone or combined with compost to replace a significant portion of the substrate currently supplied by pine bark and peat moss. The objective of this study was to evaluate wheat straw and horse manure compost, locally available resources, as components of container media for establishing and overwintering daylily (Hemerocallis fulva ‘Stella D'Oro’). A standard commercial, sphagnum peat-based substrate was amended with either wheat straw, horse manure compost, or a combination of the two. Stella D'Oro daylily divisions were grown in each substrate mix and overwintered in an unheated structure for eight months. Physical properties of the mixes were determined to be within production standards and media shrinkage was minimal. Daylilies in all substrate combinations were of comparable vigor to the non-amended substrate when growth resumed in the spring.

(291) Plant Regeneration through Direct Somatic Embryogenesis in Homalomena `Emerald Gem'

Homalomena `Emerald Gem' is an important ornamental foliage plant and widely used for interior plantscaping. Current propagation of this cultivar has been primarily carried out through in vitro culture by organogenesis; regeneration through somatic embryogenesis has not been documented. This report describes successful plant regeneration via direct somatic embryogenesis from explants of different organs. Somatic embryos formed at and around the cut surface of petiole, spathe, and peduncle explants. Embryos also appeared at the base between expanded ovaries of the spadix segment, and around midrib of leaf explants. The optimal treatments for somatic embryo occurrence from petiole, spathe, and peduncle explants were MS medium containing 0.2 mg/L NAA or 0.5 mg/L 2, 4-D with 2.0 mg/L CPPU, and for spadix explants were MS medium with 0.5 mg/L PAA and 2.5 mg/L TDZ. Somatic embryos appeared 6 to 8 weeks after culture and formed large embryo clumps in 3 to 4 months. Somatic embryos produced more secondary embryos and geminated on induction medium. Multiple shoot development and plant regeneration occurred from somatic embryo clusters on MS medium without hormone or with 2 mg/L BA and 0.2 mg/L NAA. The regenerated plants grew vigorously after transplanting to a soilless container substrate in a shaded greenhouse.

Regeneration of Syngonium podophyllum ‘Variegatum’ through direct somatic embryogenesis

A simple and effective method of regenerating Syngonium podophyllum ‘Variegatum’ via direct somatic embryogenesis has been established. Leaf and petiole explants were cultured on Murashige and Skoog (MS) medium supplemented with N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU) or N-phenyl-N′-1,2,3-thiadiazol-5-ylurea (TDZ) with either α-naphthalene acetic acid (NAA) or 2,4-dichlorophenoxyacetic acid (2,4-D). Somatic embryos directly formed at one or two sides of petiole explants on MS medium supplemented 2.5 mg l−1 TDZ with 0.5 mg l−1 NAA or 2.0 mg l−1 TDZ with 0.2 mg l−1 NAA or with 0.2 and 0.5 mg l−1 2,4-D, respectively. The frequency of petiole explants with somatic embryos produced was as high as 86% when cultured on medium containing 2.5 mg l−1 TDZ with 0.5 mg l−1 NAA. Up to 85% of somatic embryos were able to germinate after transferring onto medium containing 2.0 mg l−1 6-benzylaminopurine (BA) and 0.2 mg l−1 NAA. Approximately 50–150 plantlets were regenerated from a single petiole explant. However, there was no somatic embryo formation from leaf explants regardless of growth regulator combinations used. Regenerated plantlets from petiole explants were stable and grew vigorously after transplanting to a soilless container substrate in a shaded greenhouse.

Suppression of Seedling Damping-Off Caused by Pythium ultimum, P. irregulare, and Rhizoctonia solani in Container Media Amended with a Diverse Range of Pacific Northwest Compost Sources

ABSTRACT Suppression of seedling damping-off disease caused by Pythium spp. and Rhizoctonia solani is a potential benefit of formulating soilless container media with compost. Thirty-six compost samples from Pacific Northwest commercial composting facilities were analyzed for a number of physical, chemical, and biological properties, including suppression of damping-off caused by Pythium ultimum, P. irregulare, and R. solani. The samples were produced from diverse feedstocks and composting technol ogies; this was reflected in a large degree of variability in the measured properties. When mixed with sphagnum peat moss and inorganic aggregates, 67% of the compost samples significantly suppressed P. irregulare damping-off of cucumber, 64% suppressed P. ultimum damping-off of cucumber, and 17% suppressed damping-off of cabbage caused by R. solani. Suppression of Pythium damping-off was related to the potential of compost to support microbial activity and a qualitative index of ammonia volatilization. Suppression of Rhizoctonia damping-off was not related to any one compost factor. Currently available compost products potentially could provide commercially acceptable control of damping-off caused by Pythium spp., but it is necessary to fortify composts with microbial antagonists for the control of R. solani.

Direct somatic embryogenesis and plant regeneration from leaf, petiole, and stem explants of Golden Pothos

Somatic embryos directly formed at cut edges or on the surface of leaf explants, around cut ends or along side surfaces of petiole and stem explants of 'Golden Pothos' [Epipremnum aureum (Linden & Andre) Bunt.] on Murashige and Skoog (MS) medium supplemented with N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) or N-phenyl-N'-1, 2, 3-thiadiazol-5-ylurea (TDZ) with alpha-naphthalene acetic acid (NAA) and a medium called MK containing MS salts with Kao's vitamins, supplemented with 2.0 mg/l TDZ and 0.2 mg/l NAA. Somatic embryos were also produced on MS medium containing 2.0 mg/l kinetin (KN) and 0.5 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) from leaf and petiole explants, MS medium supplemented with 2.0 mg/l CPPU and 0.5 mg/l 2,4-D from petiole and stem explants, and 2.0 mg/l TDZ and 0.2 mg/l or 0.5 mg/l 2,4-D from stem explants. In addition, somatic embryos occurred from stem explants on Chu's N6 medium containing 2.0 mg/l CPPU and 0.2 mg/l NAA. Somatic embryos matured and grew into multiple buds, shoots, or even plantlets after 2-3 months on the initial culture medium. Germination was optimal on MS medium containing either 2 mg/l 6-benzylaminopurine (BA) and 0.2 mg/l NAA or 2 mg/l zeatin and 0.2 mg/l NAA. Shoots elongated better and roots developed well on MS medium with no growth regulators. Approximately 30-100 plantlets were regenerated from each explant. The regenerated plants grew vigorously after transplanting to a soil-less container substrate in a shaded greenhouse.

Compost Tea as a Container Medium Drench for Suppressing Seedling Damping-Off Caused by Pythium ultimum

ABSTRACT Compost tea is being used increasingly in agricultural production to control plant diseases. However, there has been limited investigation relating disease control efficacy to various compost tea production methods, particularly compost tea produced with active aeration and additives to increase microbial population densities in compost tea. Aerated compost tea (ACT) and nonaerated compost tea (NCT), produced with or without additives, was investigated for the suppression of damping-off of cucumber caused by Pythium ultimum. Compost tea was used to drench soilless container medium inoculated with P. ultimum; effect on damping-off ranged from not suppressive to consistently suppressive depending on the method used to produce the tea. The most consistent formulation for damping-off suppression was ACT produced with kelp and humic acid additives. Producing ACT with a molasses-based additive inconsistently suppressed damping-off; evidence suggests that residual nutrients can interfere with disease suppression. Heating or diluting compost tea negated suppression. Across all compost tea samples, there was no significant relationship of bacterial populations, measured as active cells, total cells, or CFU, to disease suppression. However, for all ACT produced without the molasses-based additive, there was a threshold of bacterial population density (6 log(10) active cells per ml, 7.48 log(10) total cells per ml, or 7 log(10) CFU per ml) above which compost teas were suppressive.

Evaluation of commercial inorganic and organic fertilizer effects on arbuscular mycorrhizae formed by Glomus intraradices

Formation and function of arbuscular mycorrhizae (AM) are affected by levels of fertility in soil or fertilizers applied to soilless container mixes. For AM fungi, phosphorus (P) is the main element influencing colonization of host plant roots. The question addressed in this study was whether inorganic or organic fertilizers were more compatible with the formation and function of AM. Several controlled-release inorganic (CRI) fertilizers were compared with several organic (OR) fertilizers at different rates (½× to 4× the recommended rate) to determine (1) threshold levels of tolerance by the AM fungus Glomus intraradices in relation to root colonization, and (2) growth responses of `Guardsman' bunching onion (Allium cepa) and `Orange Cupido' miniature rose (Rosa spp.) plants grown in a soilless potting mix or sandy loam soil. AM colonization in soil was greatly decreased or totally inhibited by CRI fertilizers with high P content at the 2× rate or greater, whereas colonization was decreased but never eliminated by low-P OR fertilizers at the 3× rate or greater. Shoot growth of onions was similar with or without AM inoculation when fertilized with CRI, but in general was only enhanced by OR fertilizers if inoculated with AM fungi, compared to the noninoculated controls. Shoot and root growth of onions were significantly increased by AM inoculation when OR fertilizers were used at the 1× rate. In contrast, root growth was not increased by the combination of CRI fertilizers and AM fungal inoculation. Inoculation of miniature roses grown in sandy loam amended with 25% peat and perlite and fertilized with all the CRI or OR fertilizers resulted in high AM colonization, but without much AM-induced growth increase except where OR fertilizers or CRI fertilizers with low P were used. In a soilless potting mix, growth of miniature roses was less with OR fertilizers at the rates used than CRI fertilizers, but mycorrhiza formation was greater in the former unless P was low in the latter. These results indicate that release of nutrients from organic fertilizers, as a result of microbial activity, favors AM establishment and function more than most inorganic fertilizers unless P levels of the latter are low.

The influence of humic acids derived from earthworm-processed organic wastes on plant growth

Some effects of humic acids, formed during the breakdown of organic wastes by earthworms (vermicomposting), on plant growth were evaluated. In the first experiment, humic acids were extracted from pig manure vermicompost using the classic alkali/acid fractionation procedure and mixed with a soilless container medium (Metro-Mix 360), to provide a range of 0, 50, 100, 150, 200, 250, 500, 1000, 2000, and 4000 mg of humate per kg of dry weight of container medium, and tomato seedlings were grown in the mixtures. In the second experiment, humates extracted from pig manure and food wastes vermicomposts were mixed with vermiculite to provide a range of 0, 50, 125, 250, 500, 1000, and 4000 mg of humate per kg of dry weight of the container medium, and cucumber seedlings were grown in the mixtures. Both tomato and cucumber seedlings were watered daily with a solution containing all nutrients required to ensure that any differences in growth responses were not nutrient-mediated. The incorporation of both types of vermicompost-derived humic acids, into either type of soilless plant growth media, increased the growth of tomato and cucumber plants significantly, in terms of plant heights, leaf areas, shoot and root dry weights. Plant growth increased with increasing concentrations of humic acids incorporated into the medium up to a certain proportion, but this differed according to the plant species, the source of the vermicompost, and the nature of the container medium. Plant growth tended to be increased by treatments of the plants with 50–500 mg/kg humic acids, but often decreased significantly when the concentrations of humic acids derived in the container medium exceeded 500–1000 mg/kg. These growth responses were most probably due to hormone-like activity of humic acids from the vermicomposts or could have been due to plant growth hormones adsorbed onto the humates.

Effects of a Microbial Inoculant on Plant Growth and Rhizosphere Bacterial Populations of Container-grown Plants

A commercially available microbial inoculant (Plant Growth Activator Plus) that contains 50 microorganisms, primarily bacteria, was evaluated in a soilless container substrate to determine its effects on root bacterial populations and growth response of container-grown plants at three fertilizer rates. The tropical ornamental plants included hibiscus (Hibiscus rosa-sinensis `Double Red'), spathiphyllum (Spathiphyllum `Green Velvet') and areca palm (Dypsis lutescens). The bacterial groups enumerated were fluorescent pseudomonads, actinomycetes, heat-tolerant bacteria, and total aerobic bacteria. Analysis of the inoculant before its use determined that fluorescent pseudomonads claimed to be in the inoculant were not viable. The plant variables measured were plant color rating, shoot dry weight and root dry weight. Only hibiscus shoot dry weight and color rating increased in response to the addition of the inoculant to the substrate. Hibiscus roots also had a significant increase in the populations of fluores-cent pseudomonads and heat-tolerant bacteria. From a commercial production point of view, increasing fertilizer rates in the substrate provided a stronger response in hibiscus than did addition of the microbial inoculant. Furthermore, use of the inoculant in this substrate did not compensate for reduced fertilizer inputs.

Phosphate and Potassium Retention and Release during Chrysanthemum Production from Precharged Materials: II. Calcined Clays and Brick Chips

Soilless container media have almost no capacity to retain PO4 or K. The nutrient retention of two calcined clays, attapulgite and arcillite, and brick chips, precharged with PO4 and K, was investigated. These could serve as an alternative slow-release fertilizer when incorporated into a soilless medium as a component of the mix. Sorption curves were developed at 25 °C for attapulgite of two particle sizes (0.8 to 1.6 mm and 1.6 to 3.2 mm), arcillite (1.1 to 3.2 mm), screened pieces of brick (1.0 to 3.6 mm), and a medium of 7 sphagnum peat: 3 perlite (v/v) using solutions of KH2PO4 (P at 0 to 20,000 mg.L-1). Curves indicated that PO4 and K sorption were similar for both particle sizes of attapulgite, so only the larger size [1.6 to 3.2 mm (8 to 16 mesh)] was used in greenhouse studies. Materials were evaluated in greenhouse studies by growing 'Sunny Mandalay' chrysanthemum [Dendranthema ×grandiflora Kitam. (syn. Chrysanthemum morifolium Ramat.)]. The precharged materials were tested at 10%, 20%, and 30% by volume of a peat: perlite root medium. Phosphate, K, and pH were determined on unaltered medium solutions collected throughout the cropping cycle and foliar analyses were determined on tissue collected at midcrop and end of the crop. Data indicated that precharged calcined clays retained and released PO4, and to some degree K, over time. Precharged clays did not provide K at levels which met plant needs during the latter half of the cropping cycle, but it was released and used at appreciable levels during the first month of crop production. Growth of plants receiving PO4 solely from precharged attapulgite and arcillite at 20% of the medium volume was not significantly different from that of a commercial control when the leaching fraction was maintained at 0.2. However, release of PO4 from the brick chips was not enough to match plant demand. Phosphate lost through leaching from the precharged clays was reduced by about two-thirds compared to control plants fertilized with P at 46.5 mg.L-1 from water-soluble fertilizer at each watering.

Growth of Tomato and Coreopsis in Response to Coir Dust in Soilless Media

We examined the efficacy of coir dust (CD)—the short fibers and dust from the mesocarp of coconuts (Cocos nucifera L.)—as an alternative to sphagnum peat (SP) in 50 SP : 50 vermiculite (% volume) medium. Shoot dry mass of coreopsis (Coreopsis lanceolata L.) or `Red Robin' tomato (Lycopersicon esculentum Mill.) after 5 weeks' growth in up to 50 CD : 50 vermiculite (% volume) was similar to that in 50 SP : 50 vermiculite and a commercial peat-lite (Pro-Mix BX). These growth responses depended on preplant controlled-release fertilizer (CRF) [Osmocote 17N-3.9P-10.8K at 11.5 lb/yd3 (4 kg·m−3)] and/or a post-transplanting weekly solution fertilization (SF) at 350 ppm (mg·L−1) N from 21N-2.2P-16.6K. Compared to SP, CD had lower bulk density and cation exchange capacity (volume basis) and higher C to N ratio, pH, total porosity, and container capacity. We conclude that CD is an adequate alternative to SP in soilless container media.

Evaluating Rhizon Soil Solution Samplers as a Method for Extracting Nutrient Solution and Analyzing Media for Container-grown Crops

The rhizon soil solution sampler (RSSS) currently is being used for in situ extraction of the soil solution for nutrient analysis of mineral soils used to produce field-grown crops. In this study, laboratory and greenhouse experiments were conducted to test the effectiveness of the RSSS for in situ solution extraction from soilless container root media and to compare an RSSS extraction method for measuring root-medium pH, electrical conductivity (EC), and NO3-N and K concentrations with that measured with the saturated media extract (SME) method. A near 1:1 correlation was found between the pH, EC, and NO3-N and K concentrations measured in the extracted solution of the RSSS and SME method in media without plants and in media from ten species grown using three water-soluble fertilizer concentrations applied by subirrigation. More testing is needed with the RSSS, perhaps using composite samples form several pots for analysis. The RSSS shows promise for nutrient extraction in container-grown crops because it is fast, nondestructive, simple, economical, and has minimal effect on the nutritional status of the medium in the pot.

Using Precharged Zeolite as a Source of Potassium and Phosphate in a Soilless Container Medium during Potted Chrysanthemum Production

Most soilless container root media have limited ability to retain nutrients. Zeolites are minerals of substantial cation exchange capacity that can be precharged with K, and possibly PO4, and used as a component of soilless media as a slow-release nutrient source. A zeolite clinoptilolite (Cp) was charged with K and PO4 at two concentrations and combined at 20% of the mix with sphagnum peat (60%) and perlite (20%) to evaluate its use as the sole source of these nutrients during production of Dendranthema ×grandiflorum (Ramat.) Kitamura `Sunny Mandalay.' Phosphate, K, Na, and pH were determined on unaltered bulk root medium solutions collected over the course of production, and foliar analyses were determined on tissue collected at the middle and end of the crop. All leachate was collected and analyzed to allow for the creation of K and PO4 budgets. Plants that relied on precharged Cp at the low and high rates to meet their K needs and received a N/P/-K fertilizer had similar dry mass and tissue K concentrations as the control plants that received a complete fertilizer. The use of precharged Cp at the low rate reduced K losses through leaching to 23% of the amount lost from control plants receiving water-soluble fertilizer (WSF). Plants that relied on precharged Cp for their PO4 had a lower dry mass and tissue P levels than those of the complete control treatment. However, PO4 concentrations in the root medium solution were above acceptable levels during the first month of production and should be considered when developing a fertilizer application strategy using Cp precharged with PO4.

Comparison of Pour-through and Ceramic Cup Methods of Extracting Nutrients from a Pine Bark Substrate

The pour-through (PT) nutrient extraction method involves collection of leachate at the container bottom that results from displacement of substrate solution by water applied to the substrate surface. The PT is a convenient and effective means of monitoring the nutritional status of the soilless container substrates used in the nursery industry, but is less convenient for large containers, particularly those used in the “pot-in-pot” system of growing trees in production containers within in-ground socket containers. We describe a simple vacuum method of extracting solution from pine bark in containers using ceramic cup samplers. When N was applied to a pine bark substrate at 56–280 mg/L, extractable N was slightly higher for the PT than for the ceramic cup method. The correlation between applied and extractable N was 0.99 for both methods. Further comparison of pine bark extract nutrient and pH levels for PT and ceramic cup methods will be presented.

Monopotassium phosphate as a phosphorus and potassium source for greenhouse‐winter‐grown cucumber and muskmelon1

Glasshouse experiments were conducted at the Newe Ya'ar Research Center in the winter seasons of 1992/93 and 1993/94 to examine a phosphorus/ potassium (PK) fertilizer for cucurbit crops. Monopotassium phosphate [(MKP), KH2PO4] was found to be very effective as a P and K source for cucumber (Cucumis sativus L.) and muskmelon (Cucumis melo L.) plants grown in soilless container conditions. The efficiency of MKP was essentially not different from that of the combination of phosphoric acid (H3PO4) and potassium chloride (KCl) which is widely used in the commercial production of vegetables. Appropriate fertilization of cucumbers with MKP in 1992/93 affected late‐season yield more than early‐season yield. Deficiency of P and K in Gala muskmelon inhibited vegetative growth and decreased yield. The reduced yield resulted from both less fruit‐setting and smaller fruit size. The MKP rates required by cucumber plants in 1993/94 depended primarily on growth medium composition. Generally, plants grown in inert tuff (volcanic gravel) and sandy media responded more significantly to MKP than did those grown in media rich in organic matter. There are at least three reasons for preferring the use of MKP, first it is much safer to handle than is H3PO4, second it is highly soluble and can be easily incorporated in fertigation systems, and third it has a high PK content.