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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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James E. Altland, James C. Locke, Wendy L. Zellner and Jennifer K. Boldt

The primary component in greenhouse potting substrates is sphagnum peatmoss. Substrate solution pH of nonamended peatmoss ranges from 4.0 to 4.5 ( Landis, 1990 ). Optimum substrate pH has been determined for economically important crops such as

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Matthew D. Taylor, Rachel Kreis and Lidia Rejtö

pH, and inconsistency between batches ( Hummel et al., 2014 ; Stoffella and Kahn, 2001 ). Since there are endless ingredients for making compost, the efficacy and rates for using each of these in greenhouse production are not well-understood ( Murray

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Youbin Zheng and Mary Jane Clark

will allow for efficient Sedum plant production to meet the increasing industry demand. Growing substrate pH influences plant growth and performance, and different plant species have optimal substrate pH ranges that are unique ( Reed, 1996

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Diane M. Camberato, James J. Camberato and Roberto G. Lopez

rates, target tissues, environmental conditions at application, and dosage ( Whipker et al., 2003 ). Spray solution water quality, particularly pH and alkalinity [presence of bicarbonates (HCO 3 − ) and carbonates (CO 3 −2 )], may also play a role in PGR

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Charles S. Krasnow and Mary K. Hausbeck

., 2012 ). Poinsettia grown in a Pythium -infested potting medium adjusted to pH 4.0–4.5 remained healthy compared with plants grown in an infested potting medium at pH levels >5.5 ( Bateman, 1962 ; Bolton, 1980 ). Substrate pH can also influence the

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Matthew D. Taylor, Paul V. Nelson and Jonathan M. Frantz

During the 1980s, many geranium producers observed a sporadic, unexplained decline in substrate pH. During the same time period, they also reported the occurrence of toxic concentrations of Fe or Mn in leaf tissue ( Bachman and Miller, 1995 ). In

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Matthew D. Taylor, Paul V. Nelson and Jonathan M. Frantz

Sudden pH decline (SPD) describes the situation where crops growing at an appropriate pH rapidly (within 1–2 weeks) cause the substrate pH to shift downward one to two units. Phosphorus (P) deficiency has been shown to cause plants to acidify

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Wan-Yi Yen, Yao-Chien Alex Chang and Yin-Tung Wang

the influence of root substrate and fertilizer on substrate pH. The addition of 20% sphagnum peat to fir bark resulted in a lower initial pH and more severe decline in substrate pH than fir bark alone ( Wang, 1998 ; Wang and Konow, 2002 ). Since the

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Xiaoxin Shi, Lili Yang, Guijun Yan and Guoqiang Du

secondary metabolite production ( Bourgaud et al., 2001 ; Cheng et al., 2008 ). The most commonly used culture medium is the Murashige and Skoog (MS) medium ( Murashige and Skoog, 1962 ) or the variant of it. The pH of the medium is generally suggested as 5