pH Buffering Test A protocol to determine pH buffering of horticultural substrates using a mineral acid (HCl) drench Jinsheng Huang and Paul Fisher LimeR Series Analyzing Lime in Container Substrates

Objectives To quickly measure substrate pH buffering capacity using an HCl acid drench (40 meq per liter of substrate).

Principle Substrate-pH buffering capacity refers to the ability of a substrate to maintain a stable pH following addition of acid or base. Our research shows that residual lime content is the main factor that contributes to pH buffering in container media. For a pre-limed container medium, pH buffering can be quantified by measuring pH changes following one dose of 40 meq HCl drench per liter of substrate.

Example: pH changes after one dose of 40 meq HCl per liter of substrate for 11 media

Relationship between initial residual CCE and pH buffering

Substrate pH buffering using HCl drench versus greenhouse trials with an ammonium fertilizer

pH 4.5 buffering capacity estimated using HCl titration

Table 1. Suggested ranges of pH buffering based on a survey of tested ten commercial media using one dose drench of 40 meq HCl acid per liter of substrate. pH Buffering Range ∆pH after 40 meq HCl drench Residual CCE (g/L of substrate) Low<-1.9<1.0 Medium-1.9 to – 3.0 High-1.0 – 0.0>3.0

Procedures Reagent –0.5 N HCl: dilute 42mL HCl from concentrated 36% (12M) hydrochloric acid to 958 mL deionized water, then standardize with standard 0.25N NaOH. 0.5N HCl

Procedures Measure 200 mL substrate sample in an open plastic bag. Measure 6 bags for each sample and divide into two sets, with 3 bags per set.

Procedures For the 1st set of 3 bags (Set I), add enough distilled water to raise moisture level to appropriately 95% container capacity. For the 2nd set of 3 bags (Set II), add one dosage of 40 meq HCl per liter of substrate to the substrate samples. For 0.5N HCl, it will be equivalent to 16 mL HCl for a 200 mL substrate sample. Then use deionized water to bring moisture level to appropriately 95% container capacity. Leave the plastic bag open at room temperature (20 o C) for gas exchange. (Samples can be placed in warm temperature around 30 o C for fast lime reaction).

Procedures Measure substrate-pH after 7 days. ∆pH= average pH for Set II– average pH for Set I. Use table to interpret pH buffering based on calculated ∆pH value. pH Buffering Range ∆pH after 40 meq HCl drench Low<-1.9 Medium-1.9 to -1.0 High-1.0 – 0.0

Thank You Jinsheng Huang Kate Santos Angelica Cretu Connie Johnson Ernesto Fonseca Easton Horner Becky Hamilton Dustin Meador Bill Argo, Blackmore Co. Paul Nelson, North Carolina State Univ.

Research partners (Univ. of Florida, Univ. of Minnesota)Research partners (Univ. of Florida, Univ. of Minnesota) –Leading Media and Fertilizer Companies: –Leading Growers: -AgriStarts (FL), Altman Plants (CA), D.S. Cole Growers (NH), Four Star (MI), Florida Plant Specialists (FL), Knox (FL), Kube Pak (NJ), Lucas (NJ), Pleasant View Gardens (NH), Spring Meadow (MI), Smith Gardens (WA), Twyford (FL), Wagners (MN), Welby Gardens (CO) Research partners (Univ. of Florida, Univ. of Minnesota)Research partners (Univ. of Florida, Univ. of Minnesota) –Leading Media and Fertilizer Companies: –Leading Growers: -AgriStarts (FL), Altman Plants (CA), D.S. Cole Growers (NH), Four Star (MI), Florida Plant Specialists (FL), Knox (FL), Kube Pak (NJ), Lucas (NJ), Pleasant View Gardens (NH), Spring Meadow (MI), Smith Gardens (WA), Twyford (FL), Wagners (MN), Welby Gardens (CO) 2008 Donors PINDSTRUP MOSEBRUG A/S