Quantifying the pH-Response of a Peat-based Medium to Application of Basic Chemicals

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·m 3 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% KHCO 3 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 KHCO 3 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 KHCO 3 increased. Effect of flowable lime was greater (up to 2.9 units) at lower starting-pHs, whereas KHCO 3 was less affected by starting-pH. Medium-EC increased by <0.6 dS·m -1 following single applications of all solutions.