Agriculture Reference
In-Depth Information
Interlude 2: Conventions Used in This Topic
The Decimal Mark (Decimal Point)
The decimal mark is what separates whole units from tenths, hundredths etc. In
European countries (except the UK and Ireland), in SouthAmerica (except
Ecuador), and in SouthAfrica, the decimal mark is a comma: 1,01 means one and
one one-hundredth (1+ 1/100 th ) . In NorthAmerica, India, EastAsia, andAustralia
the period or dot is used instead: 1.01 means one and one one-hundredth. This
gets even more confusing when commas or dots are used to separate large
numbers into groups. 1.000.000,00 means one million and no hundredths in many
countries; the same would be written 1,000,000.00 in English speaking and many
other countries.
The 22nd General Conference on Weights and Measures declared in 2003 that
"the symbol for the decimal marker shall be either the point on the line ( . ) or the
comma on the line ( , ). It further ruled that "numbers may be divided in groups of
three in order to facilitate reading; neither dots nor commas are ever inserted in
the spaces between groups". Thus one million may be written 1 000 000,00 or 1
000 000.00 .
In this topic we will use the dot or period ( . ) to separate the whole numbers
from the fractional decimals, and will separate groups of three with only a space,
e.g.:
1 000 000.001 (one million and one one-thousandth)
Weight of Soil Per Unit of Area
In the examples in this topic we will generally be dealing with the “plow layer”, the
upper horizon, the topsoil. We will assume that the plow layer of a hectare of
land weighs 2 000 000 (two million) kg , and the plow layer of an acre of land
weighs 2 000 000 lbs. In most soils this will be the top 15 to 17 cm of one
hectare , or the top 6 to 7 inches of one acre .
Parts Per Million ppm
In the next several chapters we will be writing a soil mineral Rx based on the
results of a Mehlich 3 soil test. The units we will be using are parts per million
(ppm) of weight .
One gram is one ppm of one million grams (1000 kg or 1 metric ton)
1 milligram is 1 ppm of 1 kilogram
1 pound is 1 ppm of 1 000 000 pounds
On a large field one will be calculating for 2 million kg of soil per hectare (2 million
lbs/ac) or more; for a greenhouse one may be calculating how much to add to a
few kilograms of potting soil mix. Working with ppm allows us to do the
calculations once, in a simple manner, and then apply them to any units of weight
we wish: grams, pounds, ounces, kilograms, or tons, and to any area: ares,
hectares, square meters, acres, square feet, cubic meters or cubic yards.
 
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