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William R. Argo and John A. Biernbaum

Hybrid impatiens were grown in 15 cm pots containing one of six root medium. After seven weeks, plant available water holding capacity (AWHC) was measured as the difference between the drained weight of the plant and pot after a one hour saturation and the weight of the pot when the plant wilted. Water absorption potential (WAP) was calculated as the capacity of each root medium to absorb applied irrigation water up to the AWHC and was measured at two moisture levels with top watering (two leaching fractions), drip irrigation (two leaching fractions) and flood subirrigation. Top watering moist media (initial AWHC = 35%) with leaching fractions of 30+ % was me most efficient method of rewetting media and was the only irrigation method tested to obtain WAP's of 100%. In comparison, flood subirrigation was the least efficient method of rewetting media with WAP of 27% for dry media (initial AWHC = 0%), and obtained a total WAP of 55% for moist media (initial AWHC = 23%). In media comparisons, the incorporation of a wetting agent into a 70% peat/30% bark mix at planting increased the WAP compared to the same media without a wetting agent with nine of the ten irrigation treatments.

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Marc van Iersel and Jong-Goo Kang

Subirrigation is an economically attractive irrigation method for producing bedding plants. Because excess fertilizer salts are not leached from the growing medium, salts can accumulate in the growing medium. Fertilizer guidelines developed for overhead irrigation may not be appropriate for subirrigation systems. Our objective was to quantify the effect of the fertilizer concentration (N at 0, 135, 285, and 440 mg·L–1) on whole-plant CO2 exchange and growth of subirrigated pansies. Whole plant CO2 exchange rate (net photosynthesis and dark respiration) was measured once every 10 min for 31 days. Whole-plant photosynthesis, dark respiration, and carbon use efficiency increased during the experiment. Fertilizer concentration started to affect the growth rate of the plants after approximately 7 days. Maximum photosynthesis and growth were achieved with N at about 280 mg·L–1 in the fertilizer solution [electrical conductivity = 2 dS·m–1]. Growth was reduced by ≈10% when the plants were fertilized with N at 135 and 440 mg·L–1 compared to 280 mg·L–1. Growth of plants watered without any fertilizer was greatly reduced, and plants showed symptoms of N and K deficiency. The size of the root system decreased and the shoot: root ratio increased with increasing fertilizer concentration, but the size of the root system was adequate in all treatments. These results indicate that subirrigated pansies can tolerate a wide range of fertilizer concentrations with relatively little effect on plant growth.

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Marc van Iersel

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.

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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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ALLEN G. SMAJSTRLA

The use of microirrigation in Florida citrus production has increased rapidly in recent years. Most new groves are now being developed with microspray or drip irrigation. Many existing sprinkler and seepage (subirrigation) systems have also been converted to micro irrigation. Although water management districts have encouraged the use of micro irrigation for water conservation, research results which solved problems with the practical implementation of this technology and which demonstrated economic incentives are primarily responsible for its popularity in Florida citrus production. Research programs have (1) developed management techniques to eliminate emitter clogging, (2) demonstrated the effective use of microspray systems for freeze protection, (3) increased young tree growth with respect to conventional irrigation methods, (4) demonstrated the cost-effectiveness of microirrigation, and (5) developed management techniques for efficient use of water and nutrients in fruit production.

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ALLEN G. SMAJSTRLA

The use of microirrigation in Florida citrus production has increased rapidly in recent years. Most new groves are now being developed with microspray or drip irrigation. Many existing sprinkler and seepage (subirrigation) systems have also been converted to micro irrigation. Although water management districts have encouraged the use of micro irrigation for water conservation, research results which solved problems with the practical implementation of this technology and which demonstrated economic incentives are primarily responsible for its popularity in Florida citrus production. Research programs have (1) developed management techniques to eliminate emitter clogging, (2) demonstrated the effective use of microspray systems for freeze protection, (3) increased young tree growth with respect to conventional irrigation methods, (4) demonstrated the cost-effectiveness of microirrigation, and (5) developed management techniques for efficient use of water and nutrients in fruit production.

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Robert L. Geneve, Jack W. Buxton, and Myra Stafford

Capillary mat subirrigation provides uniform water in the growing medium to optimize seedling growth in plugs. It also offers a closed system that allows the grower to regulate the amount of water available to seedlings and to reduce water runoff. However, root outgrowth into the capillary mat can be a significant problem. Copper hydroxide (Spin Out) was painted on the bottom, outside surface of the plug container to control root outgrowth into the capillary mat. Three square and two octagonal plug sizes were treated with copper. Regardless of the plug size or shape, copper treatment was an effective treatment to control root outgrowth in marigold seedlings. Copper treatment reduced overall root outgrowth by 80% to 92%. Marigold and geranium seedlings in copper-treated square plug containers showed some reduced shoot and root development during plug production, but there were no differences in copper-treated plants compared to nontreated plants following transplanting to cell packs.

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Patricia R. Knight, D. Joseph Eakes, Charles H. Gilliam, and Harry G. Ponder

Seed geranium (Pelargonium × hortorum Bailey `Scarlet Elite') were grown in subirrigation troughs in 10-cm pots from 25 June to 3 August 1993. Production medium was a 1 pine bark:3 peat moss:1 perlite (v:v:v) mixture. Plants were irrigated using fresh or recycled solutions and fertilized using Peter's Geranium Special 15N-6.5P-12.5K or Osmocote 14N-6.1P-11.6K. Controlled release fertilizer produced greater shoot dry weights and foliar color ratings than plants receiving water soluble fertilizer. Plants receiving a controlled release fertilizer had lower shoot N concentrations than plants receiving water soluble fertilizer. Recycled irrigation solutions reduced plant quality regardless of method of fertilization.

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Robert G. Anderson and Robert Hadad

A segment of the greenhouse crop market would like to obtain vegetables and herbs that are certified organic. The technology for the use of biological controls for insects and diseases is well-developed and a significant part of greenhouse vegetable production. Organic fertilizers, however, have not been well-utilized in organic greenhouse vegetable production. Common organic fertilizers were analyzed for the levels of nutrients when mixed with water for use in greenhouse fertigation. Products derived from algae-Algamin (liquid) and Ohrstrom's Garden Maxicrop (powder), Bat Guano, and products derived from fish waste-GreenAll Fish Emulsion (liquid) and Mermaid's Fish Powder, demonstrated nutrient levels comparable to typical water-soluble fertilizers used for greenhouse plant production. Although the organic fertilizers could not be used as a concentrate for injector systems, readings from a conductivity meter were directly related to nitrate nitrogen levels and could be used for fertilizer management in the capillary mat subirrigation system used for plant production.

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James B. Calkins, Bert T. Swanson, Daniel G. Krueger, and Karin R. Lundquist

A study was designed to ascertain the efficacy, water use efficiency, runoff potential, and cost effectiveness of four container irrigation systems: overhead sprinkler irrigation, in-line trickle irrigation, capillary mat with leaky hose, and sub-irrigation. Results were species dependent. Plant growth was best under capillary mat and trickle irrigation treatments, however, differences in plant growth and performance between irrigation treatments were minimal. Differences in water use, however, were quite significant. Overhead irrigation was inefficient regarding water use while capillary mat and trickle systems used much lower volumes of water. Conservative irrigation systems which maintain acceptable plant growth using less water and reduce runoff from container production areas can clearly benefit growers by reducing production and environmental costs.