Agriculture Reference
In-Depth Information
The
average weight per cubic meter
of a
mineral soil
will be 2 000 000kg / 1500
m
3
=
1333 kg/m
3
.
Working With Lightweight Mixes and High Organic Matter Soils
The figures above are close enough for heavy mineral soils, but naturally
high-organic matter soils such as peat soils or virgin forest soils may weigh much
less than 92 lbs per cubic foot or 1333 kg per cubic meter. Lightweight potting
media may weigh as little as 10 lbs/ft
3
(270 lbs/yd
3
) or 150 kg/m
3
.
If you are working with a light weight soil, potting media, or compost/organic matter
it is best to measure and weigh an oven-dry sample. Lightly packa 1 gallon or a 4
or 5 litre container with the dry sample and weigh the soil (of course subtracting the
weight of the container).
Calculating the Amount Needed Per Cubic Yard: Lightweight Soils
There are 7.48 (~7.5) US Gallons (128 fluid oz) per cubic foot and 201.96 (~200)
gallons per cubic yard.
If a gallon of soil weighs 2 lbs, a cubic foot will weigh 7.5
gallons x 2 lbs = 15 lbs.At 200 US gallons per yard
3
, 2 lbs x 200 gallons = 400 lbs
per cubic yard.
Once we know the weight per cubic yard we can calculate how many pounds or
fraction of a pound equals 1 ppm. The cubic yard of growing media above weighs
400 lbs. One-millionth of that: 400 lbs / 1 000 000 = 0.0004 lbs; 4 ten-thousandths
of a pound.Agood digital scale can weigh that amount, but it's awkward. We
could choose to work with ounces and decimal fractions of an ounce:
1 lb = 16 oz, so 0.0004 lb x 16 = 0.064 oz
but it's usually simpler and easier to convert the pound weight to kilograms and
grams for small amounts of soil media or amendments
Our cubic yard above weighed 400 lbs.
1 kg = 2.20 lbs.
Divide 400 lbs by 2.2 kg/lb = 182 kg per cubic yard.
A kilogram is 1000 grams.
There are
1000 milligrams in a gram
.
1000 x 1000 = 1 million.
A milligram is 1 ppm of a kilogram.
Our worksheet says we need 300 ppm Calcium. For
each kilogram
of weight,
we
need
300 ppm or 300 milligrams
(0.3 grams) of Calcium
.
Multiply 182 kg x 0.3 grams/kg = 54.6 grams of Calcium needed per cubic yard.
Calculating the Amount Needed Per Cubic Meter
There are 1000 liters per cubic meter.
The 5 liters we talked about weighing
above are equal to five thousandths or 0.005 of 1 cubic meter. If 5 liters of soil
weighs 1 kg, the weight per cubic meter would be 1 kg / 0.005 = 200 kg.
