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Theo J. Blom and Brian D. Piott

High-volume top irrigation (Chapin) was compared to subirrigation (ebb and flow) using 15-cm-diameter (1.56 liter) pot-grown chrysanthemums [Dendranthema ×grandiflorum (Ramat.) Kitamura] with peatwool (50 peatmoss: 50 granulated rockwool) as the growing substrate. Preplant moisture contents (25%, 125%, and 250%, gravimetric) and compaction (0, 20, and 50 g·cm-2) of the peatwool were also studied. Shrinkage of growing substrate was large (>309'6 of pot volume) when peatwool in the pots was not compacted. Compaction reduced shrinkage and produced plants with larger leaves, more fresh weight, and longer stems than without preplant compaction. Drainable pore space, container capacity, and total porosity was not affected by compaction. The higher preplant moisture contents increased drainable pore space but had no effect on plant growth. Chapin-irrigated plants had significantly more fresh weight (+ 24%) at the pea-size bud stage than plants grown in the ebb-and-flow system. The difference in growth was similar at flowering but significant only at P = 0.08. Soluble salts concentration in the peatwool and foliar nutrient contents differed at flowering for the two irrigation systems.

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Albert T.Y. Mak and D.M. Yeh

Effects of nitrogen application on growth, stomatal conductance, transpiration, and chlorophyll content were studied in Spathiphyllum Schott 'Sensation' grown in sphagnum peat (SP)- and coir dust (CD)-based media with top-irrigation or subirrigation. Maximum shoot dry weight occurred at 8 mM N in plants grown in SP-based medium under top-irrigation and subirrigation, and in CD-based medium under subirrigation. For plants in CD-based medium under top-irrigation, maximum shoot dry weight was obtained at 16 mm N. In SP- or CD-based medium, shoot dry weight was greater at 4 and 8 mm N under subirrigation than under top-irrigation. Stomatal conductance and transpiration were reduced by nitrogen deficiency (0 N), greatly enhanced by 4 mm N, and decreased gradually at higher N levels. Chlorophyll content increased with increasing N concentration up to 8 mm. The percentage of maximum total dry weight increased quadratically as leaf N content increased from 1.5% to 3.5%. Nitrogen at 16 and 32 mm increased the number of leaves with marginal necrosis. Reduced growth and more leaves with marginal necrosis occurred in SP- or CD-based media with EC > 1.25 dS·m-1 in the middle and bottom layers.

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John M. Dole, Janet C. Cole, and Sharon L. von Broembsen

`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.

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N.S. Khoury, E.J. Holcomb, J.W. White, and M. Rand

Recycled subirrigation systems are a possible solution to grower concerns over water use, ground water pollution, and regulations concerning these. The objectives of this experiment were to examine the differences between top- and subirrigated plants, with different fertilizer regimes and with mulches.

Six treatments of `Crimson Fire' and `Victoria' CVI geraniums were grown in 11 cm. pots. Treatments were: top irrigation, 100% N supplied with 20-10-20 soluble fertilizer; subirrigation, 100% N supplied with 20-10-20 soluble fertilizer; subirrigation, N supplied in equal portions of 20-10-20 soluble fertilizer and CRF, gel mulch; subirrigation, N supplied with CRF, gel mulch; subirrigation, N supplied in equal portions of 20-10-20 soluble fertilizer and CRF, wool mulch; subirrigation, all N supplied with CRF, wool mulch.

`Crimson Fire': fresh weight was not significantly different between top- and subirrigation; fresh weight at the same fertilizer level was not significantly different with either a gel or a rockwool mulch; all CRF resulted in the lowest fresh weights. `Victoria': top irrigated fresh weight was significantly higher compared to subirrigated. Gel mulched plants resulted in significantly lower fresh weights than wool mulched plants. All CRF resulted in the lowest fresh weights.

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Jaime K. Morvant, John M. Dole, and Janet C. Cole

Euphorbia pulcherrima `Gutbier V-14 Glory' were grown with 220 mg·liter–1 N (20N–4.4P–16.6K) using ebb-and-flow (EF), capillary mat (CAP), microtube (MIC), and hand-watering (HAN) and were irrigated either daily (pulse - P) or as needed (regular - R). For all irrigation systems, pulse irrigation produced the greatest total dry weight. HAN-R produced lower total dry weight than all other irrigation systems and frequencies. Root dry weight was highest with pulse subirrigation (EF and CAP). MIC-P, EF-P, and EF-R were the most water-efficient treatments. The experiment was repeated twice with similar results. In a second experiment, Pelargonium ×hortorum `Pinto Red' root balls were sliced into three equal segments; top, middle, and bottom. For all irrigation systems, root counts were lowest in the top region. EF root counts were greatest in the middle region, while MIC root counts were greatest in the bottom region. The two subirrigation systems had higher average root counts than the two top-irrigated systems (HAN and MIC). In general, there was less difference in EC between regions for top-irrigated than for subirrigated root balls. The EC was lowest in the bottom and middle regions of EF and the bottom region of MIC and CAP. For subirrigation, the highest EC was in the top region. For all systems, pH was lowest in the bottom region.

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N.S. Khoury, E.J. Holcomb, J.W. White, and M. Rand

Excessive electroconductivity measurements have been observed in the surface layer of subirrigated substrates. A hydrophilic gel and rockwool were used as pot mulches in order to reduce the surface layer salt buildup by absorbing the salts and/or reducing evaporation.

Six treatments of `Crimson Fire' and `Victoria' CVI geraniums were grown in 11 cm. pots. Treatments were: Trt 1 - top irrigation, N source 20-10-20; trt 2 - subirrigation, N source 20-10-20; trt 3 - subirrigation, N source in equal portions of 20-10-20 and CRF, gel mulch; trt 4 - subirrigation, N source CRF, gel mulch; trt 5 - subirrigation, N source in equal portions of 20-10-20 and CRF, wool mulch; trt 6 - subirrigation, all N source CRF, wool mulch.

Pots were divided into 3 equal volume portions. Electroconductivity, as a measure of soluble salt (SS) level, was taken. All treatments had increasing SS levels with increasing pot height. Trt 2 had surface layer salt levels significantly higher than trt 1. `Victoria' trts 3,4,5 and 6 surface layers had significantly lower SS levels than trt 1 surface layers. `Crimson Fire' trt 4's surface layer had significantly lower SS levels than the surface layer of trt 1. Trts 4 and 6 bottom layers of both cultivars had significantly lower SS levels than all other treatments.

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Connie N. Johnson, Paul R. Fisher, Jinsheng Huang, Richard P. Vetanovetz, and William R. Argo

In current horticultural practice, potential acidity or basicity of fertilizers is estimated using Pierre's method (PM) expressed in calcium carbonate equivalents (CCE) per unit weight of fertilizer. PM was developed using mineral field soil systems and may be inaccurate for quantifying fertilizer acidity in containerized plant production given the widespread use of soilless substrates and fertigation. The PM-predicted acidity of an ammonium-based fertilizer was compared against experimental data obtained when ‘Ringo’ geraniums [Pelargonium ×hortorum (Bailey. L.H.)] and ‘Super Elfin’ impatiens [Impatiens wallerana (Hook. F.)] were grown in 70% peat:30% perlite (v:v) limed with either hydrated limestone only (HL) or a combination of carbonate and hydrated limestone (CHL). Plants in 10-cm-diameter (0.35 L) containers were top-irrigated with a total of 2.0 L over 6 weeks using a 15.2N–1.9P–12.6K fertilizer [100% of nitrogen (N) as NH4-N] applied with each irrigation at 100 mg N/L without leaching. According to PM, 61.8 meq of fertilizer acidity was applied per liter of substrate. During the experiment, the pH of the substrate decreased from 7.05 to 4.41 for the HL substrate and from 7.14 to 5.13 for the CHL substrate. A corresponding drop in substrate-pH was observed when 37.1 (HL) or 43.3 (CHL) meq of CCE from 0.5 N HCl was applied per liter of substrate in a laboratory titration of the same substrates without plants. Gasometric analysis of residual carbonate at Day 0 and at the end of the experiment quantified change in CHL substrate alkalinity with time, resulting in an estimated 30.7 meq of neutralized alkalinity. Using an electroneutrality approach that assumed anion uptake (NO3 , P2O5 ) was basic, and cations (NH4 +, K+) were potentially acidic, nutrient analysis of the substrate at the beginning and end of the experiment estimated that an average 48.5 meq of acidity was contributed by the fertilizer. Experimentally measured acidity values were 13.1 to 31.1 meq·L−1 of substrate lower for HL and CHL than those expected from PM, suggesting PM overestimated the amount of fertilizer acidity applied to the substrate. These results support the need for an alternative method to predict fertilizer acidity for plant production in soilless substrates.

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Lee Ann Moccaldi and Erik S. Runkle

were top irrigated with acidified well water supplemented with a water-soluble fertilizer to provide micronutrients: 40 mg·L −1 N, 4 mg·L −1 P, 40 mg·L −1 K, and 5 mg·L −1 Ca ( Pramuk and Runkle, 2005a ). Seedlings were grown until deemed ready for

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Jasmine Jenji Mah, David Llewellyn, and Youbin Zheng

). Growing conditions. The potted bulbs were placed on benches in a greenhouse with no supplemental lighting and held at (mean ± sd ) 13.8 ± 0.7 °C until emergence (18 d). On 8 Dec. 2017, each pot was top-irrigated with ≈200 mL of solution made with 20N–3.4P

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Jasmine J. Mah, David Llewellyn, and Youbin Zheng

/night temperatures were set at 25 °C/22 °C for Expt. 2. The CO 2 concentration for both experiments was ≈440 ppm. Seedlings were top-irrigated as needed with tap water until cotyledons were visible on 50% of the plugs. Thereafter, groundwater supplemented with water