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Lime reaction rate in a container substrate is influenced by temperature and moisture, which are factors that vary between batches of substrate during manufacturing, storage, and crop production. The effects of temperature and moisture on the duration required to achieve a stable substrate-pH are useful information for substrate companies and growers, as well as a key component when modeling lime reaction over time. The pH of a 70 peat : 30 perlite (by volume) substrate was quantified over time under a range of different storage temperature (1.9 to 33.3°C) and substrate volumetric water content (VWC, 0.168 to 0.568 L of H2O/L of substrate). The lime source was a horticultural dolomitic carbonate limestone screened to the fraction that passed through a 100 US mesh but was retained on a 200 US mesh (0.075–0.15 mm) incorporated at 2.67 g·L−1 of substrate. Experiments provided two data sets for calibration and validation. Lime reaction rate increased with increasing substrate temperature and substrate moisture level. The duration required to reach a target substrate-pH value of 6.0 was used to indicate 90% of maximum pH effect from lime. Duration varied from 4 days with the combined high temperature (20.6 and 33.3 °C) and high VWC (0.468 and 0.568 L H2O/L of substrate) to 53 days with low temperature (1.9 °C) and low VWC (0.168 L H2O/L of substrate) for the calibration data set. At an example low VWC of 0.168 L of H2O/L of substrate, the duration required to reach substrate-pH 6.0 at 1.9, 7.8, 10, 20.6, and 33.3°C was 53, 38, 34, 23, and 17 days, respectively. Similarly, if the temperature was held constant at 33.3°C, reducing VWC from 0.568 L H2O/L to 0.128 L H2O/L would decrease lime reaction rate from 100% to 21%, requiring five times the duration to reach an equilibrium pH. Results can be used to compare the relative effects of moisture and temperature on lime reaction rate for substrate manufacturers and growers. [ABSTRACT FROM AUTHOR]

The objective was to quantify the extractable micronutrient levels from container substrate components and limestone and their potential contribution as fertilizer sources for crop growth. Samples of horticultural limestone (29 samples) and substrate components [peat (48 samples), perlite (10), vermiculite (14), bark (15), and coconut coir (6)] were analyzed for micronutrient content with the SME (Saturated Medium Extract) method using either water (SMEW) or diethylenetriamine pentaacetate (SMED) as extractants for the substrate components, or following acid digestion of limestone samples. Samples were obtained from commercial substrate and greenhouse companies throughout the U.S. and Canada. Peat included 36 peat samples from two peat bogs in Alberta Canada to evaluate whether species composition, decomposition, and bog location affected micronutrient content. Increasing von Post decomposition increased SMEW and SMED Mn level and SMED Zn. As percent Sphagnum fuscum increased, extractable Fe and Mn levels increased for both extractant types, and SMEW extractable Zn increased. Based on established SME guidelines for acceptable to optimum nutrient levels for soilless substrates, peat and bark could potentially provide sufficient Fe and Mn to contribute to plant requirements. Average Fe content in limestone was 0.11%, and Mn content was 0.012%. Based on SMED extractions and lime analysis, Fe supplied by 100% peat and lime could potentially provide Fe at levels comparable with commercial pre-plant fertilizers if these Fe sources are plant-available. Substrate-pH affected solubility of Fe, Mn and Zn in peat. As substrate-pH increased, Fe and Zn solubility in peat decreased with both SMEW and SMED. The SMEW-extractable Mn decreased with increasing pH, in contrast to SMED-extractable Mn which increased as pH increased. Analysis of raw materials using SMED (substrate components) or complete digestion (limestone) is advised for substrate companies to proactively identify batches of components that may affect crop nutrition. Given this high level of potential contribution of Fe by peat and lime, it is likely that these uncontrolled sources contribute to nutrient uptake in horticultural production. However, further research is required to compare extractable micronutrients with actual plant uptake. [ABSTRACT FROM AUTHOR]

Greenhouse propagation of unrooted plant cuttings is characterized by short container cell height and high irrigation frequency. These conditions can result in high moisture level and low air content in soilless container substrates ("substrates"), causing delayed growth of adventitious roots and favoring root disease. The objective of this study was to quantify and compare substrate water and air relations for three propagation substrates (peat, rockwool, and phenolic foam) that variedwidely in physical characteristics using fourmethods: 1) evaporationmethod with a tensiometer, 2) frozen columnmethod, 3) gravimetric analysis, and 4) X-ray computed tomography (CT) analysis. Moisture retention curves based on evaporation (1) and the frozen column (2) resulted in differences for peat, but similar curves for rockwool and foam. The frozen column method was simple and low cost, but was constrained by column height for peat, which had a higher water potential compared with the other two substrates. Substrate porosity analysis at container capacity by gravimetric or CT methodswere similar for volumetricwater and air content (VWCand VAC) in rockwool and foam, but differed for peat for VWC and VAC.Gravimetric analysis was simple, rapid, and low cost for whole-cell analysis, but CT further quantified spatial water and air relations within the cell and allowed visualization of complex water and air relations in an image. All substrates had high water content at container capacity ranging from 67%to 91%VWC with 5%to 11%VAC in the short propagation cells, emphasizing the need for careful irrigation management. [ABSTRACT FROM AUTHOR]

The objective was to refine protocols to quantify rooting of plant cuttings and the water/air microenvironment of substrates using x-ray computed tomography (CT). Poinsettia (Euphorbia pulcherrima) cuttings were propagated in three substrates (peat, rockwool, and phenolic foam) at varied moisture levels. In Experiment 1, adventitious rooting occurred in cuttings grown in rockwool or foam from 12% to 86% volumetric water content (VWC) and 12% to 80% volumetric air content (VAC). The highest root growth occurred in rockwool at 59% VWC and 33% VAC. There was an advantage to quantifying root growth by CT in rockwool and foam, in contrast to peat, because of clear differences in material density between root and substrate during image processing. In Experiment 2, root growth was quantified in peat by two-dimensional image scans under similar growth chamber environments, with rapid root growth from 52% to 63% VWC and 16% to 26% VAC. In Experiment 3, CT was used to quantify the substrate microenvironment at 0.5 cm slices to further describe the environment at the base of the plant cutting. Rapid rooting occurred in microenvironments above 56% VWC and 14% VAC, whereas the low 3% VAC in foam at high moisture may limit root growth. Abbreviations: volumetric water content (VWC), volumetric air content (VAC), volumetric solid content (VSC) [ABSTRACT FROM AUTHOR]

• This study quantified micronutrient Fe and Mn uptake in floricultural plants from peat without applied Fe/Mn in fertilizer. • Greenhouse tests revealed distinct responses to Fe and Mn availability in marigold and petunia. • A comparison was made between the extractable levels of Fe and Mn in peat and the actual uptake by plants. • Tested peat showed a high potential for providing Fe and Mn in quantities sufficient for the initial growth of marigold. • The study provides insights for optimizing nutrient management, benefiting horticulture and the scientific community. Peat substrates have the potential to function as micronutrient sources such as iron (Fe) and manganese (Mn). Typically, when planning fertilization program for crops, the components of peat substrates are not taken into account. The objective was to quantify potentially plant-available micronutrients of Fe and Mn from peat substrates by floriculture species when no additional Fe and/or Mn were applied in the fertilizer solution. Greenhouse experiments were conducted using Tagetes erecta 'Atlantis Primrose' marigold (iron-efficient) and Petunia x hybrida 'Celebrity Pink Morn' petunia (iron-inefficient) to compare extractable Fe and Mn from two peat sources with actual plant uptake of these nutrients by the plants. In Experiment 1, marigold was grown hydroponically in plastic tubs using four different nutrient solutions: complete, without Fe, without Mn, and without both Fe and Mn. Within a period of less than two weeks after transplant, the absence of Fe and Mn severely limited marigold growth. The hydroponic study highlighted the importance of providing both Fe and Mn nutrients immediately after sowing to support normal marigold growth. In Experiment 2, both marigold and petunia were grown from seed in two peat substrates (Blackmore seedling peat "BM peat" and Sunshine Professional Black Bale peat "SG peat") and an acid-washed sand substrate. Each peat was limed at 3 g.L−1 of reagent grade CaCO 3 resulting in an initial substrate-pH of 5.0 for SG peat and 5.5 for BM peat. Four nutrient solutions [(a) complete, or complete with (b) no Fe, (c) no Mn, and (d) no Fe or Mn] were applied with each irrigation without leaching. Initial substrate nutrient levels were extracted using the SME (saturated medium extract) method using either water (SME W) or 0.005 M DTPA (diethylenetriamine-pentaacetic acid, SME D) as extractants. Over a 5-week period (during the vegetative, non-blooming stage), peat substrates provided sufficient Fe and Mn for marigold, but iron deficiency symptoms were observed in marigolds grown in sand without Fe fertilizer. Petunia plants developed iron deficiency symptoms in all substrates without Fe fertilizer. The absence of Mn fertilizer, however, did not have a significant impact on petunia growth and health, indicating that peat substrates likely provided adequate Mn for non-symptomatic petunia plant growth. The micronutrient Fe and Mn budget analysis suggested that the SME W method underestimated the availability of Fe and Mn to the plants, whereas the SME D method may have overestimated the extractable Fe and Mn levels in relation to the actual tissue uptake. Overall, the peat substrates showed a high potential for providing Fe and Mn in quantities sufficient for the initial growth of iron-efficient marigold, but was inadequate for iron-inefficient petunia. [ABSTRACT FROM AUTHOR]

Floriculture species differ in their effect on substrate-pH and the resulting substrate micronutrient availability in container production. The objective was to quantify effects of floriculture plant species on substrate-pH. In a growth chamber factorial experiment, 15 floriculture species were grown in 70%:30% by volume peat:perlite substrate and fertilized with nutrient solutions containing 100 mg⋅L-1 N and NH4+-N:NO3--N nitrogen ratios of 0:100, 20:80, or 40:60. The relationship between substrate-pH and milliequivalents (meq) of acid or base per unit volume of substrate was quantified by titration with hydrated dolomitic lime or HCl. After 33 days, species and solution type effects on substrate-pH and estimated meq of acid or base produced were evaluated. Final substrate-pH ranged from 4.83 for geranium in 40:60 solution to 6.58 for lisianthus in 0:100 solution, compared with an initial substrate-pH of 5.84. This change in substrate-pH corresponded with a net meq of acid or base produced per gram of tissue dry mass gain (NMEQ) ranging across solutions and species from 1.47 of base for lisianthus in the 0:100 solution to 2.10 of acid for coleus in the 40:60 solution. With the 0:100 solution, geranium produced the greatest NMEQ of acid (0.07), whereas lisianthus produced the greatest NMEQ of base (1.47). Because all N in the 0:100 solution was in the NO3- anion form, meq of both anions and cations taken up by plant roots could be calculated based on tissue analysis. With the 0:100 solution, species that took up more anions than cations into plant tissue tended to have a more basic effect on substrate-pH, as would be expected to maintain electroneutrality. Data were used to estimate the percent NH4+-N of total N in a nutrient solution that would be neutral (results in no substrate-pH change) for each species. This neutral percent NH4+-N of total N ranged from ≈0% (geranium) to 35% (pentas). Species were separated into three clusters using k-means cluster analysis with variables related to NMEQ and anion or cation uptake. Species were clustered into groups that had acidic (geranium and coleus), intermediate (dusty miller, impatiens, marigold, new guinea impatiens, petunia, salvia, snapdragon, and verbena), or basic (lisianthus, pansy, pentas, vinca, and zinnia) effects on substrate-pH. Evaluating the tendency to increase or decrease substrate-pH across a range of floriculture species, and grouping of plants with similar pH effects, could help predict NH4+:NO3- ratios for a neutral pH effect and assist growers in managing substrate-pH for container production. [ABSTRACT FROM AUTHOR]

Two experiments were run to validate a "Nitrogen Calcium Carbonate Equivalence (CCE)" model that predicts potential fertilizer basicity or acidity based on nitrogen (N) form and concentration for floriculture crops grown with water-soluble fertilizer in containers with minimal leaching. In one experiment, nine bedding plant species were grown for 28 days in a peat-based substrate using one of three nutrient solutions (FS) composed of three commercially available water-soluble fertilizers that varied in ammonium to nitrate (NH4+:NO3-) ratio (40:60, 25:75, or 4:96) mixed with well water with 130 mg ⋅ L- calcium carbonate (CaCO3) alkalinity. Both the ammonium- nitrogen (NH4-N) content of the FS and plant species affected substrate pH. Predicted acidity or basicity of the FS for Impatiens walleriana Hook.f. (impatiens), Petunia x hybrida E. Vilm. (petunia), and Pelargonium hortorum L.H. Bailey (pelargonium) from the Nitrogen CCE model was similar to observed pH change with an adjusted R² of 0.849. In a second experiment, water alkalinity (0 or 135.5 mg ⋅ L-1 CaCO3), NH4+:NO3- ratio (75:25 or 3:97), and N concentration (50, 100, or 200 mg ⋅ L-1 N) in the FS were varied with impatiens. As predicted by the N CCE model, substrate pH decreased as NH4+ concentration increased and alkalinity decreased with an adjusted R² of 0.763. Results provide confidence in the N CCE model as a tool for fertilizer selection to maintain stable substrate pH over time. The limited scope of these experiments emphasizes the need for more research on plant species effects on substrate pH and interactions with other factors such as residual limestone and substrate components to predict pH dynamics of containerized plants over time. [ABSTRACT FROM AUTHOR]

n 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 x 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 electro-neutrality 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. [ABSTRACT FROM AUTHOR]

Unreacted residual limestone in the container substrate is key in buffering pH change over time. Our goal was to develop a substrate test protocol to measure residual lime [in units of CaCO3 equivalent (CCE)] by applying a strong mineral acid (HCl) to a substrate sample and measuring the evolved CO2 gas with a gasometric method based on a Chittick apparatus. In one experiment, CaCO3 was added to a substrate that had previously been neutralized to pH 7.35 with Ca(OH)2 so that there would be minimal CaCO3 reaction with the substrate at this high pH. The gasometric method was then used to estimate residual CCE. Measured CCE and applied CaCO3 were similar, indicating reliable CCE estimation. In a second experiment, a pH titration method was used to quantify the relationship between substrate-pH and milliequivalents of reacted base and provided an additional validation of the estimated reacted and residual CCE. The gasometric method demonstrated declining residual CCE over time as a dolomitic limestone reacted to raise substrate-pH and increasing residual CCE as applied CaCO3 concentration increased. Residual CCE in a substrate is an important property that should be considered for pH control and management in greenhouse crop production. Our results indicate that the gasometric system may be useful for optimizing lime application rate, lime source, or management of residual CCE during crop production. [ABSTRACT FROM AUTHOR]

Two experiments were completed to determine whether the form and concentration of iron (Fe) affected Fe toxicity in the Fe-efficient species Pelargonium xhortorum 'Ringo Deep Scarlet' L.H. Bail. grown at a horticulturally low substrate pH of 4.1 to 4.9 or Fe deficiency in the Fe-inefficient species Calibrachoa xhybrida 'Trailing White' Cerv. grown at a horticulturally high substrate pH of 6.3 to 6.9. Ferric ethylenediaminedi(o-hydroxyphenylacetic) acid (Fe-EDDHA), ferric ethylenediamine tetraacetic acid (Fe-EDTA), and ferrous sulfate heptahydrate (FeSO4⋅7H2O) were applied at 0.0, 0.5, 1.0, 2.0, or 4.0 mg⋅L-1 Fe in the nutrient solution. Pelargonium showed micronutrient toxicity symptoms with all treatments, including the zero Fe control. Contaminant sources of Fe and Mn were found in the peat/perlite medium, fungicide, and lime, which probably contributed to widespread toxicity in Pelargonium. Calibrachoa receiving 0 mg Fe/L exhibited severe Fe deficiency symptoms. Calibrachoa grown with Fe-EDDHA resulted in vigorous growth and dark green foliage, with no difference from 1 to 4 mg⋅L-1 Fe. Using Fe-EDTA, 4 mg Fe/L was required for acceptable growth of Calibrachoa, and all plants grown with FeSO4 were stunted and chlorotic. Use of Fe-EDDHA in water-soluble fertilizer may increase the upper acceptable limit for media pH in Fe-inefficient species. However, iron and Mn present as contaminants in peat, irrigation water, or other sources can be highly soluble at low pH. Therefore, it is important to maintain a pH above 6 for Fe-efficient species regardless of applied Fe form or concentration, in order to avoid the potential for micronutrient toxicity. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to evaluate effects of water-soluble fertilizer concentration (WSF) and substrate-pH on growth, foliar nutrient content, and chlorosis of seed geranium (Pelargonium × hortorum) “Ringo Scarlet.” Geraniums were grown for 21 days in a 70% peat-30% perlite substrate. Experiment 1 included four pre-plant lime rates (pH 3.8, 4.3, 4.8, and 5.5), and plants were irrigated using 1X, 2X, 3X, and 4X rates of a WSF containing 75N-11P-84K-72Ca-17 Mg-23S-0.375Fe-0.185 Mn-0.019Zn-0.028Cu-0.058B-0.006Mo. Iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were supplied as EDTA-chelated micronutrients. Experiment 2 included six lime rates (initial pH 3.2, 4.3, 5.2, 6.3, 7.0, and 7.5) at 2X and 4X WSF concentrations. Two forms of chlorosis were observed, consistent with micronutrient toxicity at moderately-low pH (4.3–5.2) and micronutrient deficiency at pH above 6.3. At very low substrate-pH, below 4.0, cation content decreased in leaf tissue, anion content increased, and plants appeared healthier than at pH 4.3–5.2. The decline in cation uptake at low pH was possibly the result of low substrate Ca, low-pH stress on membrane or cation channel activity, or competition between H+ and cations for root binding sites. At pH 4.3–5.2, plants were stunted, with chlorotic and necrotic spotting, necrotic leaf margins, and high tissue levels of Fe and Mn. At pH 5.5 (Experiment 1) or 6.3 (Experiment 2), plants appeared healthy. Iron and Mn declined at pH above 6.3, and interveinal chlorosis was observed. WSF concentration affected the pH range at which chlorosis occurred, intensifying toxicity symptoms at pH 4.3–5.2, and ameliorating deficiency at pH > 6.3. Results emphasize that an acceptable pH range for healthy growth can be affected by the applied fertilizer concentration. [ABSTRACT FROM AUTHOR]