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J. Norrie, M.E.D. Graham and A. Gosselin

The use of potential evapotranspiration (PET) estimates to identify irrigation timing for greenhouse tomatoes (Lycopersicon esculentum Mill.) grown in peat-based substrate was evaluated for a spring and fall crop. PET (using the Penman equation) was calculated from leaf, wet and dry bulb temperatures, and incident and reflected photosynthetic photon flux. Substrate matric potential (SMP) was monitored continuously using electronic tensiometers. Two irrigation starting setpoints (-4.5 and -6.5 kPa SMP) and two nutrient solution electrical conductivity (EC) treatments (1.5 and 3.0 dS·m-1) were factorially combined in a completely randomized design. Irrigation frequency was greater in treatments irrigated at -4.5 than at -6.5 kPa. The integral of calculated PET values was correlated with SMP for both experiments. Accumulated PET values were higher at the start of irrigation in the -6.5-kPa treatments for spring and fall crops. Nutrient solution EC did not influence irrigation frequency. Leaf pressure potential (LPP) was correlated to PET-predicted LPP (r 2 > 0.56) in plants subjected to high EC, low (-6.5 kPa) matric potential setpoint, or both treatments. PET and electronic tensiometer technology can be used jointly to improve irrigation management for tomatoes grown in peat-based substrates by more accurately responding to crop needs for water and nutrients.

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A. Jeremy Bishko, Paul R. Fisher and William R. Argo

Medium-pH above 6.4 is a common cause of micronutrient deficiency for container-grown plants, and technologies are required to correct an excessively high medium-pH. The objective was to quantify the dose response from application of several acidic materials that have been recommended for lowering medium-pH in soilless media. A 70% peat/30% perlite (by volume) medium was mixed with a preplant nutrient charge, a wetting agent and 1.5, 1.8, 2.1, or 2.4 kg·m-3 of a dolomitic hydrated lime resulting in four starting pH levels ranging from 6.4 to 7.6. Aluminum sulfate (17% Al) at 1.8-28.8 g·L-1, flowable elemental sulfur (52% S) at 3.55-56.8 mL·L-1, ferrous sulfate (20.8% Fe) at 1.8-28.8 g·L-1, Seplex-L organic acid at 0.32-5.12 mL·L-1, sulfuric acid (93%) at 0.08-2.56 mL·L-1, 21.1N-3.1P-5.8K water-soluble fertilizer at 50-400 mg·L-1 N (potential acidity 780 g CaCO3 equivalents/kg), and a deionized water control were applied at 60 mL per 126-cm3 container with minimal leaching as a single drench (except repeat sulfuric acid applications at 0.08 or 0.16 mL·L-1 and 21.1N-3.1P-5.8K treatments that were applied about every 3 days). Medium-pH and electrical conductivity (EC) were tested over 28 days using the saturated medium extract method using deionized water as the extractant. One day after application, aluminum sulfate, ferrous sulfate, and sulfuric acid lowered pH by up to 3 pH units at the highest concentrations and medium-pH remained fairly stable for the following 27 days. Flowable sulfur lowered pH gradually over the course of the experiment by up to 3.3 pH units, with no difference across the wide range in concentrations. Organic acid had minimal impact on medium-pH, and 21.1N-3.1P-5.8K did not lower medium-pH despite the fact that all nitrogen was supplied in the ammonium and urea form. At recommended concentrations, chemicals tested raised medium-EC, but not above acceptable levels for plant growth. The highest rates of aluminum and ferrous sulfates, and sulfuric acid, however, increased medium-EC by 2.0 dS·m-1 on day 1. Medium-pH-responses to acid-reaction chemicals would be expected to vary in commercial practices depending on additional factors such as lime type and incorporation rate, water alkalinity, media components, and plant interactions.

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Sabrina J. Ruis, Humberto Blanco-Canqui, Ellen T. Paparozzi and Russ Zeeck

Soilless mixes that include components of peat, perlite, vermiculite, and other organic materials are commonly used in the greenhouse industry ( Barrett et al., 2016 ; Vaughn et al., 2011 ). The most common organic component of soilless mixes is

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Jean-Charles Michel

of peat samples during desiccation and the decrease in wettability related to the degree of peat decomposition have already been shown using this method ( Michel et al., 2001 ). Both methods of contact angle measurements were coupled to the

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Denise L. Olson, Ronald D. Oetting and Marc W. van Iersel

media of peat moss, coconut coir dust, and the pure coconut coir dust.

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Jeb S. Fields, William C. Fonteno, Brian E. Jackson, Joshua L. Heitman and James S. Owen Jr.

PTSs and to compare them with traditional components of perlite and peat. The second objective was to determine MRCs for mixtures of peat and either perlite, SPW, or PWCs. Identifying similarities and differences in hydraulic properties between the two

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Janet F.M. Rippy and Paul V. Nelson

additions. The second problem arises when substrate pH drifts away from the initial target over the course of production. It is possible that within or among mires from which moss peat is harvested, there may be variation in the amount of “native” acidity to

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Paolo Sambo, Franco Sannazzaro and Michael R. Evans

Soilless root substrates (substrates) are commonly used in the production of containerized greenhouse crops. These substrates may be composed of a single material such as rockwool or block-cut peat, but in most cases, they are composites formulated

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Qiansheng Li, Jianjun Chen, Russell D. Caldwell and Min Deng

Peat has been a major component of substrates for containerized plant production since the 1960s ( Bohlin and Holmberg, 2004 ) due to its high porosity, high water-holding capacity, and relatively high cation-exchange capacity (CEC). The mining and

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Paraskevi A. Londra

material is determined by its availability, cost, and physical properties. In this study, the five substrates used were selected to cover the range of porous materials used in container plant production. All substrates were based on peat, coir, and