F rom page 8
we talk about millimetres of
rainfall we are in fact referring
to 1 mm of rain in an area
which is enough to evenly
cover the ground in that area
with a layer of water 1 mm
deep. According to SAWS,
“what is meant by 1 mm of
rainfall is rainfall equivalent to
1 litre of water in a 1 square
metre box with no runoff,
infiltration or evaporation”
which would result, if there
was no runoff, soaking in or
evaporation, of a layer of
water exactly 1mm deep.
A square metre box is not
practical to leave outside,
especially if you have animals
on your plot, so a rain gauge
is used. The standard
instrument for the measure-
ment of rainfall is the 100 mm
rain gauge. This is essentially a
circular or square UV
protected plastic funnel with a
diameter of 130 mm which is
kept in an open area, so that
it collects the rain into a
What is useful is to use !rainfall"
measuring when irrigating with
a sprinkler system.
SUMMER
vegetable patch and, before
you plant new plantings, add
generous amounts of organic
material in the form of
compost or kraal manure. If
your soil has a high clay
graduated and calibrated
use “rainfall” measuring when
content, the rain will not soak
cylinder. The measuring
irrigating with a sprinkler
in well, unless there is a
cylinder can record up to
system. To do so, simply place
heavy downpour which will
100mm of rain.
any square-sided flat con-
then leave the soil water-
A rain gauge should form part tainer or tray in the path of
logged. The organic matter
the sprinkler spray. The depth
of the garden management
will help to break up the
to which the container or tray
equipment of every small-
heavy soil.
holding, and a simple note of fills as the sprinkler deposits
droplets into it with each pass If your soil is sandy, compost
what has fallen, kept on a
will help to prevent the water
can be taken as the number
spreadsheet or as a diary
from quickly sinking right
entry, will make your watering of millimetres of precipitation
down into the groundwater,
being delivered to the plants
programme much more
being watered.
efficient.
Continued on page 10
You can make your own rain The weather people have also
assured us that temperatures
gauge out of any can, but
for the most parts are
then you will have to use a
expected to be higher
formula to measure the
throughout the country with
rainfall: the height of the
only the minimum tempera-
water in the can is equal to
tures showing signs of
the volume of water in the
can divided by the area of the uncertainty during early
opening. For most of us, life is summer. So we need to take
too short to do these calcula- precautions to make the best
of the rain that we do get.
tions.
What is useful, however, is to Examine the soil in your
9
www.sasmallholder.co.za