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Carrie L. Whitcher, Matthew W. Kent, and David Wm. Reed

The objective of this study was to quantify the optimum rates of water-soluble phosphorus (P) under constant nitrogen and potassium on the growth of new guinea impatiens (Impatiens hawkeri Bull.) `Paradise Violet' and vinca Catharanthus roseus `Pacifica Red' in soilless media in a recirculating subirrigation system. The experiment was designed so that only phosphate varied between treatments while all other nutrients remained constant. The ammoniacal N to nitrate N ratio was varied to counter balance increases in phosphate. Sodium was used as a counter ion to phosphate at higher concentrations of phosphate; sodium proved to be toxic at concentrations above 6 mm. In the new guinea impatiens experiment, there was a small increase in K due to the use of dibasic K phosphate to buffer pH. All growth parameters measured (height, leaf number, flower number, and shoot fresh and dry weight) showed significant differences with increasing P rate. Depending on the growth parameter measured, quadratic–linear models revealed an optimum P rate of 0.1 to 0.96 mm for new guinea impatiens `Paradise Violet' and 0.45 to 1.25 mm P for vinca `Pacifica Red'. For dry shoot weight, a common measure of optimum plant growth, the optimum P rate was 0.75 mm P for new guinea impatiens `Paradise Violet' and 0.67 mm P for vinca `Pacifica Red'. For flower number, a common measure of floral quality, the optimal P rate was 0.96 mm P for new guinea impatiens `Paradise Violet' and 1.25 mm P for vinca `Pacifica Red'. Electrical conductivity (EC) of the growing media increased significantly with increasing rate of P. At all rates, EC was significantly greater in the top layer than in the bottom and middle layers. The pH of the growing medium did not vary in relation to P concentration.

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Allyson M. Blodgett, David J. Beattie, John W. White, and George C. Elliott

A plantless system using subirrigation was developed to measure water absorption and loss in soilless media amended with hydrophilic polymers, a wetting agent, or combinations of these amendments. Peat-perlite-vermiculite and bark-peat-perlite controls achieved 67% and 52% of container capacity, respectively, after 20 daily irrigation cycles. Maximum water content of amended media was 78% of container capacity. Adding only a hydrophilic polymer did not increase total water content significantly. Adding a wetting agent increased water absorption in both media. However, when hydrophilic polymer and wetting agent were present, the medium absorbed more water than with wetting agent alone. More extractable water was removed from media containing wetting agent. Water loss rate by evaporation was not affected significantly by medium, hydrophilic polymer, wetting agent, or any combination of these variables.

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Mary Ann Rose and John W. White

`Celebrate 2' Poinsettias were grown for 8 weeks in a controlled-environment growth room until first signs of bract coloration. In growth stage I (GSI; weeks 1 through 4) low, medium, and high N rates (25, 75, and 125 mg N/liter, respectively) were applied by subirrigation (no leaching). Following floral induction [growth stage II (GSII), weeks 5 to 8], there were nine treatments: all possible combinations of the three N rates in GSI plus three rates (75, 125, and 175 mg N/liter) in GSII. Although >80% of shoot dry weight and >90% of total leaf area developed during growth GSII, reaching an acceptable plant size by week 8 depended on receiving adequate fertilization in growth GSI. In contrast, leaf chlorosis, noted in plants receiving the lowest rate in GSI, was rapidly reversed by increasing the N rate in GSII. Quadratic regression equations fitted to shoot dry weight and leaf area data predicted that using 125 mg N/liter in both growth stages gave maximum responses at week 8. However, using 75 mg N/liter in GSI and 125 mg N/liter in GSII also produced acceptable growth in poinsettias. Our results suggest that some growth restriction imposed by N availability during the first 4 weeks of growth may be acceptable and perhaps desirable to reduce growth regulator use and the environmental impact of overfertilization.

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William R. Argo, John A. Biernbaum, and William C. Fonteno

Medium CO2 and O2 partial pressures were measured at three locations [3.8 (top layer), 7.5 (middle layer), and 10.3 (bottom layer) cm below the rim] in 15-cm-tall pots containing flowering chrysanthemums [Dendranthem×grandiflorum (Ramat.) Kitamura] grown in one of three root media. Average ambient medium CO2 and O2 partial pressures were 63 Pa and 21 kPa, respectively, and were similar in the three sampled layers in root media with an average moisture content of 50% to 60% of container capacity. Within 10 minutes after a drip-irrigation application of well water containing a titratable alkalinity to pH 4.5 of 320 mg CaCO3/liter, the partial pressure of medium CO2 increased to ≤1600 Pa and medium O2 decreased to 20.5 kPa in the top and middle layers of the pot. With subirrigation, medium CO2 partial pressures increased to ≤170 Pa and medium O2 remained at 21 kPa. When reverse-osmosis purified water (titratable alkalinity to pH 4.5 of <20 mg CaCO3/liter) was used instead of well water, the large increase in medium CO2 did not occur, indicating that the bicarbonate alkalinity in the irrigation water was the source of CO2. The high medium CO2 partial pressure measured after irrigation was not persistent; within 180 minutes, it returned to levels averaging 45% higher (100 Pa) than that measured before the irrigation. Medium O2 also had returned to ambient levels 180 minutes after the irrigation.

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Daphne L. Richards and David Wm. Reed

New Guinea impatiens (Impatiens hawkeri Bull.) `Illusion' were grown in a recirculating subirrigation system under various rates and placements of 14N-6.1P-11.6K (Osmocote; Scotts-Sierra, Marysville, Ohio) resin-coated, controlled-release fertilizer (CRF). Four CRF placements (incorporated, top-dressed, bottom, and dibble) were tested. Incorporated placement yielded slightly greater dry weights than the other placements. A rate experiment tested incorporating from 0.5 to 2 times the fertilizer manufacturer's recommended rate of 7.11 kg·m-3. All shoot growth parameters (height, leaf number, shoot, and root fresh and dry weight) exhibited a significant quadratic response, as exemplified by shoot dry weight, where shoot dry weight increased up to the 1.5× rate, after which shoot dry weight decreased. A quadratic response surface model revealed that the optimum rate response ranged from 1.16× rate for height to 1.47× rate for shoot dry weight. The lower bound of the 95% confidence interval (CI) would be the lowest rate at which one could expect maximum growth response. The lower bound of the 95% CI varied from 0.56× rate for height to 1.30× rate for shoot dry weight. Thus, the lowest rate that would be within the 95% CI for all growth parameters, and thus yield maximum growth response, would be the 1.30× rate. Electrical conductivity (EC) of the growing media increased significantly with increasing CRF rate. At all rates, EC was significantly greater in the top layer than in the middle and bottom layers. Only in the 1.75× and 2× rates did EC exceed the recommended EC levels in the middle and bottom layer. All rates >0.75× exceeded recommended EC in the top layer. Release characteristics and total nutrient balance of the CRF was compared in subirrigated and top-watered systems. There was no significant difference between top-watered and subirrigated treatments for the amount of K recovered in plant tops and released from prills. By day 84, in subirrigation, 46% of the K was still in the prills, 41% was recovered in the plant tops, and 22% was recovered in the medium. Similar results were obtained in the top-watering treatment, except that a lesser amount was recovered in the medium (9%) and a small amount (4%) was recovered in the leachate. The uptake of K by plants and release of K by the CRF were inversely proportional and linear with respect to time. Of the K released from the prills, 77% and 83% were recovered in the plant tops for subirrigation and top-watering, respectively, indicating very high fertilizer use efficiency.

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Wen-fei L. Uva, Thomas C. Weiler, and Robert A. Milligan

Zero runoff subirrigation (ZRS) technology is a promising method of managing fertilizer and pesticide inputs while improving production efficiency. However, high capital investment costs and inadequate technical information available to growers are major impediments to initiating the change. This study quantifies costs and returns associated with adopting ZRS systems and compares the profitability of four alternative ZRS systems (ebb-and-flow benches, Dutch movable trays, flood floors, and trough benches) for greenhouse operations in the northeastern and north central United States. The capital investment analysis showed that the Dutch movable tray system was most profitable for small potted plant production, and the flood floor system was most profitable for large potted plant and bedding crop flat production. Sensitivity analysis showed that changes in cost variables generally did not affect the profitability rankings of the alternative ZRS investment projects. Nonetheless, the flood floor system gained slight advantages when the product price increased, and the Dutch movable tray system gained advantages as the hourly labor cost increased.

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Francesco Montesano, Cristina Ferulli, Angelo Parente, Francesco Serio, and Pietro Santamaria

Nutrient solutions (NS) containing moderate to high concentrations of salts are frequently supplied to improve the taste of tomato fruits grown in soilless systems. The aim of this study was to determine whether salinity and water stress affect the tomato fruit quality similarly. The research was conducted in Mola di Bari, Italy, during Autumn 2004, and compared the nutrient film technique (NFT) with the trough-bench technique [Subirrigation (SUB)] in terms of tomato (Lycopersicon esculentum Mill. cv. Kabiria) fruit quality. In the NFT, the plants were grown with two electrical conductivity (EC) levels (2–4 and 6–8 dS·m-1) of NS. The highest EC was obtained by increasing all the ions in the NS. In the SUB system, two water tensions (-4 and -8 kPa) of substrate (perlite) were examinated. At harvest, in each cluster (six/plant), fruit dry matter (DM) and total soluble solids (TSS) were determinated. In the fourth and sixth cluster, vitamin C content and titratable acidity were determined. Total yield was not influenced by either soilless system, while the average weight of the fruit was lower in the SUB. The DM and TTS were influenced by soilless system (on average, 6.6 vs 7.3 g/100 g of fresh matter and 5.3 vs. 5.9 °Brix, with NFT and SUB, respectively). Both of the stresses resulted in the increase of DM and TSS, principally in SUB (water stress) in respect to NFT (salinity stress), while vitamin C and titratable acidity were not influenced by soilless system or water/salinity stress (25.2 mg/100 g fresh matter and 0.45 g/100 mL of citric acid juice, respectively). Results of NFT with the highest EC of NS exceeded 9 dS·m-1, without any stress symptoms in the plants, while EC in the SUB system remained unchanged (about 2.5 dS·m-1).

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Stephanie A. Beeks and Michael R. Evans

require longer production times than bedding plants and are often grown in larger containers using subirrigation systems such as ebb-and-flood benches or flood floors. Therefore, the objective of this research was to evaluate the physical properties of

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Jong-Goo Kang and Marc W. van Iersel

( van Iersel, 1999 ). Subirrigation may result in more problems with the accumulation of soluble salts in the growing medium than overhead watering, because excess salts are not leached from the growing medium ( Kent and Reed, 1996 ). Even when constant

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Francesco Montesano, Gianfranco Favuzzi, Angelo Parente, Francesco Serio, and Pietro Santamaria

Sustainability of the soilless greenhouse system is under discussion in open cycle systems, where excess nutrient solution (NS) draining from the substrate is released into the environment. Closed growing systems (CGS) lead to the saving of water and fertilizers. The aim of this research was to compare two CGS: nutrient film technique (NFT) and trough-bench technique [Subirrigation (SUB)]. We report the results of yield and water use efficiency (WUE) of tomato (Lycopersicon esculentum Mill. cv. Kabiria) plants. NFT plants were grown with two electrical conductivity (EC) levels (2-4 and 6-8 dS·m-1) of NS (its highest EC was obtained by increasing all the ions therein). In the SUB system, two water tensions (-4 and –8 kPa) of susbtrate were compared; a NS with an electrical conductivity level of 2 dS·m-1 was used. The tensions were measured through tensiometers. Tomato plants were transplanted at the fourth to fifth true-leaf stage into pots containing 8 L of perlite for SUB. In both CGS, the plants were placed on steel gullies (slope of 2%). Six clusters per plant were harvested. Total and commercial yield were not influenced by the CGS (on average, 1959 and 1853 g/plant, respectively). The average weight of the fruit was lower in the SUB system's plants (40 vs. 43 g/fruit, respectively, for SUB and NFT). Salinity and water stresses resulted in a reduction of 26% of the yield and 16% of the average weight of fruits. The WUE was higher in SUB than NFT (30.7 vs. 26.0 g·L-1, respectively). Salinity stress reduced WUE (29.4 v.s 22.6 g·L-1 with 2–4 and 6–8 dS·m-1, respectively), whereas water stress did not.