Soil Treatment Video Lecture | Class 7 Oxford Science: Chapter Notes, Worksheets & Tests

limestone is also used in agriculture it
may only make up 3% of all quarried
limestone but it is essential for
neutralizing acid soils most crops don't
grow so well on acidic soils so it's
important for farmers to test their
soils after each harvest to find out how
acid or alkaline it is the pH of the
soil is measured a small amount is
placed in a glass tube adding pure water
makes a solution
the ph is tested accurately with a
specially designed indicator
after mixing the soil and the indicator
thoroughly the tube is left for a few
minutes the soil sinks to the bottom and
the color of the solution is then easy
to see this soil is too acidic is at ph
5.5 what it should be is near at ph 6.5
6.5 is almost neutral this is where
limestone comes in handy the chemical
name for limestone is calcium carbonate
spreading it over the field will
neutralize the acidic soil although you
cannot see it when calcium carbonate
mixes with the soil a chemical reaction
is slowly taking place on a small scale
the reaction can be observed more easily
using dilute acid a few drops of
universal indicator monitor the pH red
means the solution is strongly acidic
add calcium carbonate and the solution
fizzes the reaction is producing a gas
called carbon dioxide
as more calcium carbonate is added the
redness starts to fade this color change
means the solution is now less acidic a
yellow-green color indicates that it's
almost neutral acid plus calcium
carbonate produces a neutral solution
adding limestone changes the pH of the
soil salt can farmers do without it
farmers are looking to alternatives to
limestone seaweed is a possibility and
they are also using methods such as soil
testing and careful crop rotations to
reduce its use but finding an
alternative as good as limestone is
proving difficult so it looks as though
farmers will be using limestone for a
long time yet