pH Buffering TestA protocol to determine pH buffering of horticultural substrates using amineral acid (HCl) drench

Jinsheng Huang and Paul Fisher

LimeR SeriesAnalyzing 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

0

1

2

3

4

5

6

7

S1,R1.12

S2,R0.45

S3,R0.58

S4,R0.27

S5,R0.96

S6,R1.97

S7,R1.95

S8,R2.83

S9,R3.73

S10,R2.52

S11,R4.91

Substrate Number (Sx) and Initial Residual CCE (Rx)

pH

initial pH Final pH

-4.1

-1.9

-2.5-1.9-2.0

-1.8 -0.7-0.7 -0.9 -1.1

-0.6 40 meq.L-1

Relationship between initial residual CCEand pH buffering

y = 0.38x - 2.21

R2 = 0.77-3

-2

-1

0

0 2 4 6Initial Residual CCE (g·L-1)

Del

ta p

HAcid drench at 40 meq/ L

p< 0.001

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

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0Delta pH from HCl Drench (40 meq·L-1)

De

lta p

H f

rom

10

0%

NH 4

-N F

ert

ilize

r Comparison of HCl Drench and Ammonium Fertilizer

Response

p = 0.005

y = 1.24x + 0.58

R2 = 0.92

pH4.5 buffering capacity estimatedusing HCl titration

0

1

2

3

4

5

6

0 1 2 3 4 5 6

Initial Residual CCE (g·L-1)

pH

4.5

Bu

ffer

ing

Cap

acit

y

(CC

E g

·L-1

)HCl (in CCE g/L) needed to drop pH to 4.5

p < 0.001

y = 1.02x + 0.18

R2 = 0.91

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 -1.0 1.0 – 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 oC) for gas exchange. (Samples can be placed in warm temperature around 30 oC 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 HuangKate SantosAngelica CretuConnie JohnsonErnesto FonsecaEaston HornerBecky HamiltonDustin 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 Media and Fertilizer Companies:

– Leading Growers: Leading Growers:

- AgriStarts (FL), Altman Plants (CA), D.S. Cole Growers (NH), Four AgriStarts (FL), Altman Plants (CA), D.S. Cole Growers (NH), Four Star (MI), Florida Plant Specialists (FL), Knox (FL), Kube Pak (NJ), Star (MI), Florida Plant Specialists (FL), Knox (FL), Kube Pak (NJ), Lucas (NJ), Pleasant View Gardens (NH), Spring Meadow (MI), Lucas (NJ), Pleasant View Gardens (NH), Spring Meadow (MI), Smith Gardens (WA), Twyford (FL), Wagners (MN), Welby Gardens Smith Gardens (WA), Twyford (FL), Wagners (MN), Welby Gardens (CO)(CO)

• Research partners (Univ. of Florida, Univ. of Minnesota)Research partners (Univ. of Florida, Univ. of Minnesota)– Leading Media and Fertilizer Companies:Leading Media and Fertilizer Companies:

– Leading Growers: Leading Growers:

- AgriStarts (FL), Altman Plants (CA), D.S. Cole Growers (NH), Four AgriStarts (FL), Altman Plants (CA), D.S. Cole Growers (NH), Four Star (MI), Florida Plant Specialists (FL), Knox (FL), Kube Pak (NJ), Star (MI), Florida Plant Specialists (FL), Knox (FL), Kube Pak (NJ), Lucas (NJ), Pleasant View Gardens (NH), Spring Meadow (MI), Lucas (NJ), Pleasant View Gardens (NH), Spring Meadow (MI), Smith Gardens (WA), Twyford (FL), Wagners (MN), Welby Gardens Smith Gardens (WA), Twyford (FL), Wagners (MN), Welby Gardens (CO)(CO)

2008 Donors

PINDSTRUP MOSEBRUG A/S