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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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Abstract

The relationship between water extraction (1:1.5) values and nutrient uptake in geranium (Pelargonium × hortorum Bailey) growing in moss peat (peat), bark, or moss peat and soil media was investigated. Nitrogen, P, and K fertilizers were incorporated in increments in the starting media and applied again in solution, about at the crop midpoint. Desirable nutrient N(NH4 +-N + NO3 --N), P(H2PO4 --P) and K(K+) values (DV) from media analysis at the start of the experiments (MDV) and midway to flowering (FDV) also were calculated from regression equations on the basis of maximum growth rates, maximum dry weight production at midharvest, and final harvest. The relationships between plant uptake of N, P, and K and the water extract concentrations were generally very good, except for K in bark for both harvests and in peat at the first harvest, and an underestimated P uptake in peat + soil and in bark. The media DV obtained using growth data were broadly similar to those using plant dry weight data, although somewhat lower for N during the early growing period.

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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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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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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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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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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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Abstract

Sewage sludge, pharmaceutical fermentation residues, cranberry wastes, and food flavoring wastes that had been composted by in-vessel techniques were tested as substitutes for Canadian sphagnum peat in a Cornell peat-lite mix-A. Marigolds (Tagetes erecta L. ‘Lemondrop’) were grown in a medium containing 50% (by volume) vermiculite, and 0%, 10%, 20%, 30%, 40%, or 50% compost, with the remainder comprised of Canadian peat. Marigold growth was improved when any or all of the peat was replaced with composted sewage sludge. Except for media containing 40% and 50% composted food flavoring waste, plant growth in nonliquid fertilized media containing the other composts was equal or superior to conventional Cornell peat-lite mix. Except for media containing 50% pharmaceutical, 50% cranberry, or 40% or 50% food flavoring compost, plant growth was improved by supplemental liquid fertilizer. Improved growth was related to increased levels of plant nutrients, while decreased growth, at the highest proportions of compost, resulted from excessive NH4N, pH, or soluble salts. Differences in aeration, water holding capacity, and other physical media properties were small. We conclude that many types of organic wastes, composted by in-vessel techniques, can be used as a substitute for part or all of the peat in a conventional peat-lite potting media.

Open Access

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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