Leachate Electrical Conductivity Research Articles

Reassessing the Salinity Tolerance of Greenhouse Roses under Soilless Production Conditions

The performance of modern greenhouse-grown roses under intensive nutrient and water management practices questions their traditional classification as a salt-sensitive species, and emphasizes the need to reassess their salinity tolerance. Container-grown `Bridal Pink' roses (on R. manetti rootstock) in a peat moss-based growing medium were irrigated, using moderate leaching fractions (25% targeted, 37.5% actual), with complete nutrient solutions supplemented with NaCl at 0, 5, and 10 mm. These salt concentrations affected the electrical conductivity (EC) and Cl concentrations measured in the leachates, but had no significant effects on flower yield and quality over four growth and flowering flushes (§29 weeks). Cumulative yields over this period increased an average of §13% per leachate EC unit. Thereafter, the applied NaCl concentrations were increased 3-fold to 0, 15, and 30 mm and the plants continued to be evaluated for another four flowering flushes. No significant differences in cut-flower yield and quality were observed among salt treatments despite further increases in leachate EC and Na and Cl concentrations. Symptoms of salt injury were visually observed during the last three flowering cycles, and most heavily on the oldest foliage of plants receiving the highest salt concentration (30 mm), but not on the foliage of harvested shoots. The concentration of most nutrients in leaf tissue was not significantly affected by any of the treatments over the course of the experiment. Leaf Na concentrations were not affected by NaCl applications, averaging 42 mg·kg-1 across treatments. Conversely, leaf Cl concentrations increased significantly and cumulatively over time with salt additions, and ranged from 1.0 to 17.5 g·kg-1 (0.1 to 1.75%). Regression analyses revealed that average relative dry weight yields increased with leaf Cl concentrations up to 4.0 g·kg-1 (0.40%), but were depressed at higher concentrations.

MEDIA CONSTITUENTS, MICRONUTRIENT FERTILIZER SOURCE, AND CALCIUM APPLICATIONS INFLUENCE IRON, MANGANESE, AND ZINC LEACHING1*

Sphagnum moss peat (PM), perlite (PR), pine bark (PB), sand (SN), and two media formulated from these constituents (3 PM + 1 PR and 3 PB + 1 PM + 1 SN, by volume) were used to determine the effect of individual media constituents and mixes on iron (Fe), manganese (Mn), and zinc (Zn) leaching with a granular-incorporated (GIF) or a water-soluble (WSF) micronutrient fertilizer source and calcium (Ca) surface application. Leachate electrical conductivity increased with increasing Ca application rate regardless of fertilizer source. Leachate from PR and SN contained more Fe, Mn, and Zn than leachate from other media regardless of micronutrient source. More Fe leached from SN and more Mn and Zn leached from PR than from any other medium when WSF was applied. In contrast, when GIF was the fertilizer source, more Fe leached from PR, and more Mn and Zn leached from SN than from any other medium. Perlite and SN provide aeration and stability, but should be used in combination with other media components that permit ion retention in the media. *Approved for publication by the Director, Oklahoma Agricultural Experiment Station. This research was supported by project H-2324.

Fertilizer Concentration Affects Growth and Nutrient Composition of Subirrigated Pansies

Ebb- and-flow irrigation is an economically attractive subirrigation method that reduces labor costs and eliminates runoff from greenhouses. The effects of fertilizer concentration on growth of subirrigated pansy (Viola ×wittrockiana Gam.) and the leachate electrical conductivity (EC) and pH were quantified, using two growing media. Leachate EC increased as the EC of the fertilizer solution increased from 0.6 to 3.6 dS·m–1 (70 to 530 mg·L–1 N). The leachate EC was fairly constant over time when the EC of the fertilizer solution was 0.6 dS·m–1, while it increased throughout the experiment at higher fertilizer concentrations. MetroMix 300 leachate consistently had a higher EC than did MetroMix 500. Leachate pH of both growing media was similar throughout the growing season. The pH decreased over time and was lower with higher fertilizer concentrations. Optimal plant growth occurred with a fertilizer EC of 1.2 or 1.8 dS·m–1, and a leachate EC between 1.5 and 4 dS·m–1. Increasing the concentration of the fertilizer solution resulted in increased shoot tissue levels of P and Mn and decreased tissue levels of K, Mg, and Na. The results of this study indicate that pansy is not very sensitive to the EC of the growing medium and can be grown successfully in a closed subirrigation system.

132 Fertilization Methods to Match Nutrient Supply with Demand for Potted Chrysanthemum

A greenhouse study was conducted in Autumn 1998 using standard cultural practices for potted chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura] to determine how fertilization affected plant growth and quality and nutrient leaching. Fertilization treatments included constant liquid fertilization until anthesis (LFA), constant liquid fertilization until disbud (LFD), slow-release resincoated fertilizer (SRF), and no-fertilizer control. Frequency of irrigation was determined gravimetrically, and leaching fractions maintained near 0.2. Plant growth and quality for LFA, LFD, and SRF met commercial crop standards. Nearly 60% of the total nitrogen applied with LFA was applied during the 4 weeks between disbud and anthesis, due to increased water demand. During the same period when liquid fertilization was discontinued for LFD, leachate electrical conductivity (EC) levels dropped from 4 to <1 dS·m-1. Leachate EC levels for LFA at anthesis remained high, but were <1 dS·m-1 for the other treatments. LFD and SRF drastically reduced the total amount of nutrients applied during the course of production compared with LFA. Use of an appropriate slow-release fertilizer or discontinued use of liquid fertilizer at disbud allow soluble salt levels to decrease during the latter weeks of the mum production cycle, when nutrient demand is low and water demand is high.

Hydrological and geochemical factors affecting leachate composition in municipal solid waste incinerator bottom ash: Part I: The hydrology of Landfill Lostorf, Switzerland

The objective of the investigation of the municipal solid waste incinerator (MSWI) bottom ash landfill, Landfill Lostorf, was to determine the residence time of water in the landfill and the flow paths through the landfill. Over a period of 22 months, measurements of rainfall, landfill discharge and leachate electrical conductivity were recorded and tracer experiments made. Over the yearly period 1995, approximately 50% of the incident rainfall was measured in the discharge. An analysis of single rain events showed that in winter, 90–100% of rainfall was expressed in the landfill discharge, whereas in summer months, the value was between 9 and 40% depending on the intensity of the rain event. The response to rainfall was rapid. Within 30–100 h, approximately 50% of water discharged in response to a rain event had left the landfill. The discharge was less than 4 l/min for approximately 50% of the measurement periods. Qualitative tracer studies with fluorescein, pyranine and iodide clearly showed the existence of preferential flow paths. This was further substantiated by quantitative tracer studies of single rain events using 18 O / 16 O ratios and electrical conductivity measurements. The proportion of rainwater passing directly through the landfill was found to be between 20 and 80% in summer months and around 10% in winter months. The difference has been ascribed to the water content in the landfill. The average residence time of the water within the landfill has been estimated to be roughly 3 years and this water is the predominant component in the discharge over a yearly period.

Temperature and Phosphorus Source Affect Phosphorus Retention by a Pine Bark-based Container Medium

These studies were conducted to determine the effect of 1) temperature on P leaching from a soilless medium amended with various P fertilizers, 2) water application volume on P leaching, and 3) various fertilizers on P leaching during production and growth of marigolds (Tagetes erecta L. `Hero Flame'). Increasing temperature linearly decreased leaching fraction; however, total P leached from the single (SSP) or triple (TSP) superphosphate-amended medium did not differ regardless of temperature. Despite a smaller leaching fraction at higher temperatures and no change in the total P leached, P was probably leached more readily at higher temperatures. More P was leached from the medium amended with uncoated monoammonium phosphate (UCP) than from the medium containing polymer-coated monoammonium phosphate (CTP) at all temperatures, and more P was leached from UCP-amended medium at lower temperatures than at higher temperatures. More P was leached from TSP- than from SSP-amended medium and from UCP- than from CTP-amended medium regardless of the water volume applied, but leachate P content increased linearly as water application volume increased for all fertilizers tested. Plant dry weights did not differ regardless of P source. Leachate electrical conductivity (EC) was lower with TSP than with SSP. Leachate EC was also lower with CTP than with UCP. A higher percentage of P from controlled release fertilizer was taken up by plants rather than being leached from the medium compared to P from uncoated fertilizers.

Growth and Foliar Nutrient Concentrations of Crape Myrtle in Response to Disparate Climate and Fertilizer Placement in Large Nursery Containers

Abstract A study was replicated in different climates [central Arizona (arid, Sonoran desert) and southwestern Georgia (humid, temperate)] to evaluate effects of controlled-release fertilizer placement in a bark-based container substrate on growth and foliar nutrient concentrations of Lagerstroemia indica L. × L. fauriei Koehne ‘Muskogee’ in large (#7) containers. Plants in Arizona were smaller with higher shoot-to-root ratios and higher levels of N, K, P, Fe, and Cu and lower levels ofCa and Zn in foliage compared with plants in Georgia. Differences in meteorological factors such as higher maximum and minimum temperatures and solar radiation, lower rainfall, and higher container root-zone temperatures, leachate electrical conductivity and nitrate concentrations were coincident with the smaller size and higher foliar nutrient concentration of Arizona plants. Fertilizer placed at the north exposure of container substrate increased plant size in Arizona. However, compared with growth of plants in Georgia, fertilizer placement at the north exposure in Arizona was not enough to entirely alleviate size inhibition caused by the arid Sonoran desert climate.

Studies on water damage in mungbean. II. Electrical conductivity of seed leachate as an assay of level of damage

Weather-damaged seeds of mungbean are unsuitable for the production of bean sprouts and some other food uses. The breeding of resistant cultivars requires an understanding of the weathering process and the use of suitable criteria for measuring the degree of weather damage. The aim of this research was to describe the effect of weathering on the electrical conductivity of leachate from exposed seeds and to evaluate this technique as a means of discriminating among levels of weather damage. Seeds were weathered in the field or immersed in water in the laboratory for varying durations during one or more cycles of wetting and drying. Leachate conductivities generally increased with increasing visual damage and decreasing viability of seeds. When measurements of conductivity were delayed, the results appeared to be confounded by the extent to which solutes were lost during previous exposure/s to weathering. Measurements soon after immersion tended to reduce this effect and to better reflect the level of weather damage in seeds of mungbean. It was concluded that leachate conductivity technique can provide a reliable assay of weather damage in mungbean. When seeds have been exposed to severe weathering, however, the relationship breaks down, and the technique can give misleading results.

Self-watering Container Design and Salinity Affect Growth of Two Foliage Plants

Abstract Dracaena marginata L. and Spathiphyllum Schott. ‘Mona Loa’ were grown for 90 days in either one of two ‘self-watering’ containers, one plastic and one kiln-fired clay. The plastic container relied on the upward movement of water via capillary flow from a subjacent reservoir. The kiln-fired clay container was a ‘pot-within-a pot’ design with an adjacent water reservoir located between the larger and smaller pots. Water seeped horizontally through the inner pot along the pot-rooting medium interface. Reservoirs of each container were filled with either one of three levels of saline water (0.3, 1.3, or 2.3 dS/m). Rooting medium leachate electrical conductivity was lower for ‘pot-within-a-pot’ containers compared with the plastic containers. Irrespective of irrigation salinity, canopy leaf area, root length, shoot to root ratio, gas exchange values, and foliar visual quality of both species were highest for the ‘pot-within-a-pot’ containers. Also, Dracaena leaf area and dry weights were highest for the ‘pot-within-a-pot’ container. Increased irrigation salinity decreased canopy area and visual quality of Spathiphyllum. Shoot dry weight and shoot to root ratio were highest for Dracaena at the 1.3 dS/m salinity level.

Growth of Poinsettias, Nutrient Leaching, and Water-use Efficiency Respond to Irrigation Methods

`Gutbier V-14 Glory' poinsettias (Euphorbia pulcherrima Willd. Ex. Klotzsch) grown with ebb-and-flow irrigation used the least amount of water and produced the least runoff, and plants grown with capillary mats used the greatest amount of water and produced the most runoff, compared to microtube and hand-watering systems. The maximum amount of water retained by the pots and media was greatest for the microtube and ebb-and-flow systems and became progressively lower for the hand-watering and capillary mat systems. The media and leachate electrical conductivity from plants grown with subirrigation systems was higher than those grown with top irrigation. For the two top-irrigation systems (microtube and hand-watering), plants grown with 250 mg N/liter from a 20N-4.4P-16.6K water-soluble fertilizer had greater leaf, stem, and total dry weights than those grown with 175 mg N/liter. The two subirrigation systems (ebb-and-flow and capillary mat) produced plants that were taller and had greater leaf, stem, and total dry weights when grown with 175 than with 250 mg N/liter. The higher fertilizer concentration led to increased N, P, Fe, and Mn concentration in the foliage. Nitrogen concentration was higher in top-irrigated plants than in subirrigated plants. The ebb-and-flow system produced the greatest total dry weight per liter of water applied and per liter of runoff; capillary mat watering was the least efficient in regard to water applied and runoff.

Presowing Seed Treatments to Enhance Supersweet Sweet Corn Seed and Seedling Quality

Poor emergence and low seedling vigor are characteristics of many supersweet sweet corn (Zea mays L.) cultivars carrying the shrunken-2 (sh2) gene. Four sh2 sweet corn cultivar seeds [`How Sweet It Is' (HSII), `Crisp N' Sweet 711' (CNS-711), `Sweet Belle' (SB), and `Dazzle' (DZ)] were solid-matrix-primed (SMP), SMP with sodium hypochlorite (SMPcl), treated with a fungicide combination (F) (Imazalil + Captan + Apron + Thiram), or primed with the aforementioned fungicides (SMPf). The seed treatments were tested in the laboratory and the field. Seed imbibition and leachate electrical conductivity were lower in SMP seeds than in nonprimed seeds. In the field, emergence percentage and rate of CNS-711 and SB (high-vigor seeds) were not improved by the seed treatments compared to the nontreated seeds. Emergence percentage and rate of HSII and DZ (considered low-vigor seeds) were improved as a result of SMPcl, SMPf, or F treatments compared to nonprimed seeds. Compared to the F treatment, the SMPcl presowing treatment increased DZ seedling emergence rate and percentage. The combined SMP and seed disinfection via NaOCl seems to be a promising fungicide seed-treatment substitute that improves the stand establishment and seedling vigor of sh2 sweet corn cultivars. Chemical names used: 1-[2-(2,4-dichlorophenyl)-2-(2-propenyloxy)ethyl]-1 H imidazole (Imazalil); N-[(trichloromethyl)thio]-4-cyclohexene-1,2-dicarboximide(Captan); N- (2,6-dimethylphenyl)- N -(methoxyacetyl)alanine methyl ester (Apron); tetramethylthiuram disulfide (Thiram).

LEAKAGE AND MOBILIZATION OF STORAGE RESERVES DURING IMBIBITION OF SWEET CORN.

Interconversion and transport of seed storage reserves during imbibition may influence subsequent germination. Sweet corn (Zea mays L. cv. Florida Staysweet) seeds were imbibed in aerated distilled water for either 0, 3, 6,9,12, or 24 h intervals. Seed leachate electrical conductivity, leachate soluble carbohydrate concentrations, and seed moisture were quantified at each interval. Lipid, non-structural carbohydrate, and protein concentrations of embryo and endosperm tissue were quantified for each imbibition interval. After imbibition treatments, seed germination performance was evaluated at 10 and 25C. Leachate conductivity and seed moisture increased with duration of imbibition. Glucose and fructose were the major soluble carbohydrates found in the seed leachate. Embryo lipid and sucrose concentrations significantly increased within 6 h of imbibition, while endosperm lipid decreased. Endosperm sucrose concentration remained constant throughout the duration of imbibition. Germination percentage was not significantly improved at 10 or 25C during the course of imbibition. Conversely, time to germination decreased significantly at 10C within 3 h. Storage reserve mobilization during imbibition may be responsible for the decreased time to germination observed at 10C.

Leachate Electrical Conductivity and Growth of Potted Geranium with Leaching Fractions of 0 to 0.4

Geraniums (Pelargonium × hortorum L.H. Bailey `Yours Truly') were grown in a glasshouse from 15 Mar. to 9 May as single pinched plants in a growing medium with a bulk volume of 1.3 liters per 15cm diameter standard plastic pot. Plants received constant fertigation with N at 300 mg·liter-1 from 20N-4.4P-16.6K with leaching fractions (LFs) of ≈ 0, 0.1, 0.2, and 0.4. The LF is the volume of solution leached from the container divided by the volume of solution applied to the container. There were 24 irrigations during the study. Plants with LFs of 0.2 and 0.4 had 46% larger leaf area, 40% more shoot fresh mass, and 37% more shoot dry mass than plants with LFs of 0 and 0.1. By week 5, the leachate electrical conductivity (EC) at 25C for LFs of 0.1,0.2, and 0.4 had increased from ≈ 3 dS·m-1 initially to 12, 8, and 4 dS·m-1, respectively. At harvest, the EC of a saturated medium extract (ECe) was 7, 4, 3, and 2 dS·m-1 for LFs of 0, 0.1, 0.2, and 0.4, respectively. At harvest, medium EC, with LFs of 0.1, 0.2, and 0.4 was 47% 68%, and 60% less in the lower two-thirds of the pot than in the upper third. With a LF of 0, the medium EC, was `not lower in the bottom of the pot. With fertigation N at 300 mg·liter-1, minimizing the LF substantially reduced growth of container-produced geraniums. In addition to specifying LF, the number of container capacities leached per week, termed the leaching intensity (LI), should be calculated for container leaching studies. In two studies, the LFs may be the same yet the LIs can be very different.

Long-Term Land Application of Activated Sludge from a Petrochemical Wastewater Treatment Plant: I - Leachate Quality

Excess activated sludge from SITEL, the wastewater treatment plant of Polo Petroquímico do Sul (South Petrochemical Complex), Triunfo, State of Rio Grande do Sul (RS), Brazil, is disposed of by subsurface injection on pangola grass and rye grass fields at an average annual rate of 24 tons/ha (dry basis). In order to assess absorption of sludge constituents by plants, modifications of soil properties and leachate quality, a microplot growth-leaching experiment is being conducted at the Department of Soils of UFRGS since 1985. Pangola grass (Digitariadecumbens, Stent) and rye grass (Loliummultiflorum, Lam) are grown in summer and winter respectively. Some microplots have been loaded with sludge enriched with Cu, Zn, Cr, Ni, Cd, Pb and Hg since 1988. Plant nutrients such as K, Cu, Zn and B did not increase in leachate, even at the higher application rates employed. Ammonium and pH were not affected either, whilst nitrates increased at the highest application rates. Ca and Mg increased in leachate during the third and the fourth years of the experiment, probably due to the liming of the microplots. Electrical conductivity of leachate increased with sludge application. Na, chloride and sulphate, the more soluble ions, increased slowly during the first year and more rapidly during the subsequent years. Heavy metals Cr, Ni, Cd, Pb and Hg in leachate were not consistently affected by application of pure sludge or metals-enriched sludge. The concentrations of these constituents in leachate were found to be generally below accepted limits for potable water. Exacerbation of loading of metals, bringing about introduction of total amounts that exceed current limits of addition of metals to soil, did not produce significant alterations in leachate quality. This suggests that these limits are very safe with respect to protection of aquifers. The determination of nitrates in leachate at different sludge application rates made possible the adoption of 40 tons/ha.year as the maximum allowable sludge loading rate (on dry basis) for the real sludge farms at SITEL. This figure is approximately double the operational sludge application rate at SITEL.

Leachate Electrical Conductivity and Growth of Potted Poinsettia with Leaching Fractions of 0 to 0.4

Poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch `V-14 Glory') were grown in a greenhouse for 70 days in 1.3 liters of medium (13 cm deep in 15-cm pots) with a leaching fraction (LF) of ≈ 0, 0.1, 0.2, or 0.4. Plants were fertigated with 300 mg N/liter from 20 N-4.4P-16.6K. The electrical conductivity (EC) of the fertigation solution was 2.1 dS·m-1. The leachate EC increased from 2 dS·m-1 initially to plateaus of ≈ 6, 9, and 15 dS·m-1 for LFs of 0.4, 0.2, and 0.1, respectively. Poinsettia height, shoot fresh and dry mass, and leaf and bract areas were not significantly different among the LF treatments. Leachate pH decreased from 6.1 initially to 5.1 at the end, but there was no significant difference among the LF treatments. The EC of a saturated medium extract (ECe) was between 17% and 48% higher in the lower third of the medium than in the middle third. The difference was greater with a lower LF. The EC, was 8.9, 7.3, 5.2, and 3.4 dS·m-1 in the lower third of the pot for a LF of 0, 0.1, 0.2, and 0.4, respectively. Under conditions of this study, container poinsettias required no leaching.

Effect of Potassium Level on Severity of Drechslera Leaf Spot of Calathea picturata ‘Vandenheckei’

Abstract Severity of Drechslera leaf spot (Drechslera setariae) of Calathea picturata ‘Vandenheckei’ was affected by potassium fertilization rate with ½, 1 or 2 times the recommended rate (1400 g/m3) causing a reduction in number of lesions caused by Drechslera setariae compared to plants receiving no potassium. In addition, plant quality, height and number of leaves were unaffected by potassium rate during the test period. Leachate electrical conductivity was unaffected by these potassium rates and was approximately 1000 μhos/cm two months after fertilization.

Leachate Electrical Conductivity and pH for Ten Foliage Plants

Abstract Most foliage plant varieties tested produce salable plants when fertilized with a wide range of rates. About 5 grams 19N-2.6P-10K (19-6-12) per 15 cm pot per 3 months resulted in best Dracaena fragrans ‘Massangeana’, Nephrolepis exaltata ‘Compacta’, and Philodendron s. oxycardium. No more than 2.4 grams per pot appears best for Chamaedorea elegans. Aglaonema ‘Silver Queen’, Aphelandra squarrosa ‘Dania’, Codiaeum variegatum ‘Banana’, Spathiphyllum ‘Petite’, Dieffenbachia maculata ‘Camille’ and Epipremnum aureum ‘Marble Queen’ grew best at about 10 grams per pot per 3 mos. Only P. s. oxycardium and C. elegans had a narrow requirement for fertilization levels. Electrical conductivity (EC) of leachate obtained from pots of best quality plants had a very wide range indicating leachate EC is a poor indicator for production of quality plants.

POTTED GERANIUM (PELARGONIUM × HORTORUM) GROWTH WITH LEACHING FRACTIONS OF O to 0.4

Geranium `Yours Truly' in 15-cm diameter plastic pots were greenhouse-grown as single pinched plants in a completely randomized design. Plants were irrigated with 300 mg/liter N from 20N-4.4P-16.6K with leaching fractions (LF) of 0, 0.1, 0.2, and 0.4. There were 24 irrigations during the 8-week study. Plants with LF of 0.2 and 0.4 had 46% greater leaf area, 40% greater top fresh weight, and 37% greater top dry weight than plants with LF of 0 and 0.1. By week 5 the leachate electrical conductivity (EC) for LF of 0.1, 0.2, and 0.4 had increased from about 3 dS/m initially to 12, 8, and 4 dS/m, respectively. At harvest, medium ECe was 7, 4, 3, and 2 dS/m for LF of 0, 0.1, 0.2, and 0.4, respectively. At harvest, medium pH was the same in the top, middle, and bottom thirds of the pot. At harvest medium ECe with LF of 0.1, 0.2, and 0.4 was 47, 68, and 60% lower in the bottom two-thirds of the pot than in the top third. With a LF of 0 the medium ECe was not lower in the bottom of the pot. Minimizing the LF for potted geraniums substantially reduced plant growth.

Effect of Fertilizer Level on Severity of Xanthomonas Leaf Spot of Pilea spruceana

Abstract Severity of Xanthomonas leaf spot of Pilea spruceana was highest for plants receiving intermediate fertilizer rates (recommended to 5 times the recommended rate) and decreased at rates of 6–9 times recommended rate. Plant growth responded similarly with highest quality plants most susceptible to Xanthomonas campestris. Tissue nutrient content for highest quality plants was as follows: N (2.2%), P (0.37–0.38%), K (1.2–1.4%), S (1.00–1.06%), Mg (1.03–1.24%), Ca (2.07–2.30%), Fe (62–76 mg/kg), Mn (358–370 mg/kg), B (50–55 mg/kg), Cu (10 mg/kg), and Zn (348–357 mg/kg). Leachate electrical conductivity for highest quality plants was approximately 200 μmhos/cm. The results indicate that optimizing the nutrient status for highest quality foliar growth of P. spruceana may result in conditions which maximize severity of Xanthomonas leaf spot.

Response of Codiaeum variegatum ‘Gold Star’ as Influenced by Slow-Release Fertilizer

Abstract Codiaeum variegatum ‘Gold Star’ croton were grown at different nutritional levels of 3.3, 6.6, 9.9, 13.2, 16.5 and 19.8 g of slow-release 19N-3P-10K (19-6-12) per 12.5 cm (5 in) pot. Plant grade was highest with levels of 3.3–9.9 g per pot, with corresponding leachate electrical conductivity of approximately 200–1100 μmhos·cm−1.