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  • Author or Editor: A. Jeremy Bishko x
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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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The objective was to systematically quantify the dose response from applications of several alkaline materials recommended for raising pH in acidic media. A 70 peat: 30 perlite (by volume) medium was mixed with a pre-plant nutrient charge, a wetting agent, and between 0 and 1.5 kg·m3 of a dolomitic hydrated lime resulting in six starting-pHs between 3.4 and 6.4. The supernatant from a solution of Ca(OH)2, 2.5 to 40 mL·L-1 of a flowable dolomitic limestone suspension, 99.5% KHCO3 between 0.6 to 9.6 g·L-1, 85% KOH between 0.056 and 0.56 g·L-1, 15N-0P-12K water-soluble fertilizer at 50 to 400 mg·L-1 N, and a distilled water control were applied at 60 mL per 126-mL container with minimal leaching as a single drench (except the 15N-0P-12K that was applied about every three days). All chemicals increased medium-pH within one day, and pH remained stable until day 28 except for Ca(OH)2 which showed a 0.2 unit decrease in pH from day 1 to 28. The Ca(OH)2 and KOH drenches raised medium-pH by less than 0.5 units, and there was a slight decrease in pH from the 15N-0P-12K for starting-pHs lower than 5.0. Flowable dolomitic lime and KHCO3 raised pH by up to 2 pH units, averaged across starting pHs and 1-28 days after application. The effect on medium-pH increased as concentration of flowable lime and KHCO3 increased. Effect of flowable lime was greater (up to 2.9 units) at lower starting-pHs, whereas KHCO3 was less affected by starting-pH. Medium-EC increased by <0.6 dS·m-1 following single applications of all solutions.

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