pH
What is it: How to assess it:
pH is a measure of the acidity, or alkalinity of
the soil. It really measures the amount of free
hydrogen (H) and hydroxyl (OH) ions present in
soil. pH in the field can be assessed by using a pH
Colour Indicator kit (Rapauch Method). Using the
kit, a sample of soil is mixed with a solution and
then dusted with a reagent powder.
The biochemical processes that occur daily in
soils always result in a balance of acidity and
alkalinity and give a soil its pH. pH is measured as
a number from one to 14. Seven is neutral, below
seven is acidic, and above seven is alkaline. Changes in sample colour can be assessed in
good light against a colour chart to determine
the sample’s pH.
The pH levels are influenced primarily by soil
type and climate, but management also plays an
important role.
Why it is important:
Soil pH can influence a number of processes
including nutrient availability and biological
processes.
Under highly acidic or highly alkaline conditions,
a number of nutrients may become tied up and
unavailable for plant uptake.
Under acidic conditions in some land types,
elements such as aluminium may also release
and create toxic conditions for plant growth.
In many Queensland grazing landscapes, most
pasture species present have adapted to the
local pH conditions of the area. However, when
considering sowing introduced pasture species
it is useful to know the pH of the soil as some
species will not be suited to extreme pH levels.
20 - RASH MANUAL
Measuring method:
At a minimum, soil pH can be assessed at one
point along the transect. Take the sample from
the same cube of soil used to assess aggregate
strength.
Alternatively, walk 15 paces along the transect,
and, using a spade, dig out a sample of soil.
Try to keep it intact and at least 10 cm deep if
possible.
Use it to take samples for the pH test. If the
monitoring point consists of a high tussock grass
or shrub, take the soil sample directly adjacent
to the plant. Take soil from 5-10 cm deep in the
sample.
For more accurate monitoring, conduct the test
three times along the transect and calculate an
average. Walk along the transect and stop every
15 paces to dig a sample and test.
Equipment:
pH Colour Test Kit.