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Laura K. Judd and Douglas A. Cox

To test the effect of soluble salts on the growth of New Guinea impatiens (Impatiens platypetala), `Selenia' was grown for 70 days in a soilless medium and irrigated with solutions of 20N-4.3P-16.6K at rates of 0.5, 1.0, 1.5, or 2.0 g·liter-1. A fifth treatment was no fertilization for the first 14 days, 0.5 g·liter-1 for the next 14 days and 1.0 g·liter-1 till finish. At 14-day intervals shoot dry weight and growth medium soluble salts were measured. By 42 days after planting, differences between treatments were statistically significant with respect to dry weight. Over a 70-day period, growth was greatest with 0.5 g·liter-1. The 1.0 g·liter-1 treatment caused a similar growth response. Plants in delay treatment responded similarly to 0.5 and 1.0 g·liter-1. Higher rates, 1.5 and 2.0 g·liter-1, caused growth suppression and resulted in soluble salts buildup in the growth medium. Soluble salts levels of 1.5 dS·m-1 and above suppressed early growth. Results show that during the first 42-56 days of growth, New Guinea impatiens are sensitive to soluble salts and levels over 1.5 dS·m-1 are cause for concern.

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Mario Perches and Don Wilkerson

Ebb and Flood systems provide an efficient means of sub-irrigating greenhouse crops. However, substrate accumulations of soluble salts can limit plant growth.

Two treatment irrigation regimes, consisting of 1.70 EC and 0.86 EC, were applied to 7.0 cm pots filled with a standard peat:perlite growing medium. Treatment solutions were changed weekly. All containers were irrigated daily and substrate EC levels measured weekly in the upper, middle, and lower 2.33 cms of the container.

Following 6 weeks of observation, mean EC substrate levels ranged from 1.23 mmhos/cm to 4.42 mmhos/cm. Significant differences occurred between the upper and middle/bottom portions of the container. There was also a significant interaction between treatment irrigation regimes, substrate layer and week.

In both treatment regimes, salt accumulations in the middle and bottom layers of substrate were within acceptable levels for plant production.

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Bernard B. Bible and Richard J. McAvoy

`Angelika White' poinsettias (Euphoria pulcherrima Willd.ex. Klotzch) were grown hydroponically with modified Hoagland's solution concentrations of 2 or 8 mS·cm-1. The 8-mS·cm–1 rate was imposed by proportionate increases in Ca(NO3)2, KNO3, and MgSO4. Water use, whole plant fresh mass, and pan evaporation were measured gravimetrically twice weekly over a 2-week period beginning 12 Oct. 1995. Poinsettia leaf water loss (g H2O/dm2 of estimated leaf area per day) was 0.30 and 0.22 times pan evaporation (g H2O/dm2 of pan area per day) for the plants in the 2 and 8 mS·cm–1 solutions, respectively (a 25% reduction in water loss for plants in the 8 mS·cm–1 solution), as compared to plants in the 2 mS·cm–1 solution. At initial anthesis, a reciprocal transfer of plants between the 2 and 8 mS·cm–1 solutions was used to investigate the time when plants were sensitive to high soluble salts for bract necrosis. Other plants were maintained throughout the experiment in the 2 and 8 mS·cm–1 solutions. On 15 Jan. 1996, plants were harvested and total lamina surface of leaves and bracts, number of necrotic bracts, and dry mass of leaves, bracts, stems, and roots were recorded. The results indicated that exposure to high soluble salts (8 mS·cm–1) prior to anthesis significantly increased the percent incidence of bract necrosis and decreased root growth. The smaller the root dry mass as a percent of total plant dry mass the greater the incidence of bract necrosis (Y = 0.0972X2 – 3.78X + 38.7, r 2 = 0.69).

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Jaime K. Morvant, John M. Dole and Earl Allen

Pelargonium hortorum Bailey `Pinto Red' plants were grown with 220 mg·L−1 N (20N-4.4P-16.6K) using hand (HD), microtube (MT), ebb-and-flow (EF), and capillary mat (CM) irrigation systems. At harvest, root balls were sliced into three equal regions: top, middle, and bottom. A negative correlation existed between root medium electrical conductivity (EC) and N concentration to root number such that the best root growth was obtained with low medium EC and N concentrations. EF root numbers were greatest in the middle region. The two subirrigation systems (EF and CM) had higher average root numbers than the two surface-irrigation systems (HD and MT). For all irrigation systems, root numbers were lowest in the top region. In general, less difference in medium soluble salt and N concentrations existed between regions for surface-irrigated than for subirrigated root balls. Soluble salt concentration was lowest in the bottom and middle regions of EF and the bottom region of MT and CM. For subirrigation, the highest medium soluble salt and N concentration was in the top region. For all systems, pH was lowest in the bottom region. Plant growth for all irrigation systems was similar. EF and MT systems required the least water and EF resulted in the least runoff volume.

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Holly L. Scoggins and Marc W. van Iersel

Several probes have been been recently developed that can be inserted directly into the growing medium of container-grown crops to get electrical conductivity (EC) or pH measurements. However, for many floriculture and greenhouse crops, EC interpretation ranges are based on substrate solution extraction methods such as the 1:2 v/v dilution, saturated media extract (SME), and more recently, the pour-through. We tested the sensitivity and accuracy of four in situ EC probes at a range of substrate moisture content and fertilizer concentrations. We also compared results from in situ probes with currently used methods of EC measurement. Concerning the effects of substrate volumetric water content (VWC) on the in situ probes, our results indicate little differences exist among probes when VWC exceeds 0.50, though drier substrates yielded differences depending on the measurement method. The SigmaProbe and W.E.T Probe measure the EC of the pore water specifically and show a decrease in EC with increasing water content, as the fertilizer ions in the pore water becomes more diluted as VWC increases. Results with the Hanna and FieldScout probes increased with increasing water content as the added water helps conduct the current of these meters. The EC measured with the various in situ probes differed slightly among the probes, but was highly and positively correlated with all three of the solution extraction methods over the range of fertilizer concentrations. It would be possible to convert substrate EC guidelines that have been established for any of the laboratory methods for use with the in situ probes, though our results indicate the substrate VMC must be above 0.35 for the interpretation to be valid.

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Carl J. Rosen, Thomas R. Halbach and Bert T. Swanson

Composting of municipal solid waste (MSW) has received renewed attention as a result of increasing waste disposal costs and the environmental concerns associated with using landfills. Sixteen MSW composting facilities are currently operating in the United States, with many more in the advanced stages of planning. A targeted end use of the compost is for horticultural crop production. At the present time, quality standards for MSW composts are lacking and need to be established. Elevated heavy metal concentrations in MSW compost have been reported; however, through proper sorting and recycling prior to composting, contamination by heavy metals can be reduced. Guidelines for safe metal concentrations and fecal pathogens in compost, based on sewage sludge research, are presented. The compost has been shown to be useful in horticultural crop production by improving soil physical properties, such as lowering bulk density and increasing water-holding capacity. The compost can supply essential nutrients to a limited extent; however, supplemental fertilizer, particularly N, is usually required. The compost has been used successfully as a sphagnum peat substitute for container media and as a seedbed for turf production. High soluble salts and B, often leading to phytotoxicity, are problems associated with the use of MSW compost. The primary limiting factor for the general use of MSW compost in horticultural crop production at present is the lack of consistent, high-quality compost.

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Eugene K. Blythe and Donald J. Merhaut

The pour-through method was developed as a simple and rapid means of monitoring pH, soluble salts [electrical conductivity (EC)], and nutrient availability in the soil solution of containerized substrate ( Wright, 1984 , 1986 ). Solutions for

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Michael A. Fidanza, David L. Sanford, David M. Beyer and David J. Aurentz

, University Park) for processing and analysis. Laboratory tests measured the following properties: pH, carbon:nitrogen (C:N) ratio, soluble salts, solids, moisture, organic matter, carbon, total nitrogen (N), organic nitrogen, ammonium nitrogen, phosphate (P 2

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Mark V. Yelanich and John A. Biernbaum

The influence of fertilizer concentration and leaching volume on the quantity of applied N and water that were leached from a container-grown poinsettia crop (Euphorbia pulcherrima Willd.) was investigated. The NO3-N quantity leached after 71 days increased with higher NO3-N application rates (7, 14, or 28 mol NO3-N/m3) and higher leaching volumes; it ranged from 0.03 g NO3-N [7 mol·m-3, 0.00 container capacity leached (CCL)] to 7.65 g NO3-N (28 mol·m-3, 1.0 CCL). The NO3-N concentration for saturated media extracts increased with lower leaching volumes and higher fertilizer concentrations. For example, when 7 mol NO3-N/m3 was applied, NO3-N in the medium was 27.1 mol NO3-N/m3 when 0 CCL was used, but it was 8.6 mol NO3-N/m3 when 1.0 CCL was used. Shoot height and dry mass were not affected by the treatments. Leaching treatments also did not influenced leaf area, but leaf area was larger at 7 compared to 14 or 28 mol NO3-N/m3.

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William R. Argo and John A. Biernbaum

Rooted cuttings of `Gutbier V-l 4 Glory poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) were grown in 15-cm pots using two irrigation methods, two water-soluble fertilization schedules, and two preplant root-media fertilization rates. No difference in shoot growth occurred with either top watering with 33% leaching or subirrigation. The top 2.5 cm (top layer) contained nutrient concentrations up to 10 times higher than those measured in the remaining root medium (root zone) of the same pot with both irrigation methods. Constant applications of28 mol N/m3 water-soluble fertilizer (WSF) limited shoot and root growth as measured at 3 and 8 weeks compared to a weekly increase in the concentration of WSF from 0 to 28 mol N/m3 in 7 mol N/m3 increments over a S-week period. The additional incorporation of 0.27 kg·m-3 mineral N to Metro Mix 510 before planting had no effect on fresh- or dry-weight accumulation. When the root-medium surface was covered by an evaporation barrier, 46% less water and 41% less N fertilizer were applied to plants of similar size, and higher root-zone nutrient levels were maintained over the 8 weeks of the experiment. The evaporation barrier had the greatest effect on increasing root-zone nutrient concentrations and reducing the growth of subirrigated plants.