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Sphagnum peat was blended with CaCO₃ or Ca(OH)₂ and incubated for 3 weeks at 20C to achieve a pH of ≈ 4.4, 5.4, 6.2, or 7.3. An unlimed control had an initial pH of 3.5. Urea was added to medium treatments at the rate of 125 μg urea-N/cm³. Samples were incubated at 20 ± 1.0C. Medium pH, urea-N, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{2}^{-}-\mathrm{N}\) \end{document} , and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{N}\) \end{document} were measured immediately before urea addition (day 0) and 1, 2, 3, 4, 7, 14, 21, and 28 days after urea addition. Medium pH increased when urea was applied for all lime treatments. Medium pH remained at an elevated level, except for the two highest rates of C&CO₃, in which pH increased Initially, then decreased. The rate of urea hydrolysis increased as lime rate increased. For both lime sources, urea was completely hydrolyzed within 4 days for the two highest lime rates, except for the highest rate of CaCO₃. Nitrite accumulation was evident in the highest lime rate for both lime sources. Nitrate formation was greater with CaCO₃ than with Ca(OH)₂.

Abstract

Rooted Pelargonium ×hortorum L.H. Bailey ‘Yours Truly’ and ‘Irene’ geranium cuttings were planted 15 Oct. in raised beds, 11.3 liter plastic pots, 85 liter poly bags, or nutrient film systems within 2 double poly greenhouses. In one greenhouse, high pressure sodium (HPS) lamps supplemented natural light (86 µmol s^-1m^-2 ± 10 µmol s^-1m^-2) from 0800 to 2400 hr and in the other greenhouse light was not supplemented. Ambient carbon dioxide levels were enriched with an additional 300–600 ppm of carbon dioxide during daylight hours in the greenhouse without supplemental lighting and during lighted hours in the greenhouse equipped with HPS lights. Cutting number, dry weight, basal stem caliper, and the length of roots produced on harvested cuttings were recorded from 18 Nov. to 3 Jan. There were no differences among cultural systems for any of the parameters measured under natural daylight conditions. When supplementary HPS lighting was utilized, differences in number of cuttings produced and cutting dry weight were apparent, with NFT grown stock plants being the most productive. Growth differences between cultivars were evident for all parameters measured. Treatment of the stock plants was not observed to affect rooting response of cuttings.

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.