Agriculture Reference
In-Depth Information
To readily use the calculations in the following chapters
, if your soil test results
are not already in ppm, you will need to convert the numbers you have to
ppm.
Many soil testing laboratories already report their test results in ppm; some,
mostly in the USA, report in pounds per acre. If the lab you are using usually
reports in lbs/acre (or kg/hectare) you can ask them to print your soil report in ppm,
or do the conversion yourself, based on the convention
that for a depth of 6” or
15cm, 1ppm = 2 kg/hectare (or 2 lbs/acre)
. Just divide the lbs/acre or
kg/hectare result by 2.
1000 lbs/acre ÷ 2 = 500 ppm
1000 kg/hectare ÷ 2 = 500 ppm
If the soil sample was taken to a depth other than 6” or 15cm
, and the lab
results are in lbs/acre or kg/hectare, you will need to compensate for the
difference in weight. If the sampling depth is doubled to 12” or 30 cm, the weight
would be 2 x as much,
4 million lbs/acre or kg/hectare, and 1 ppm would be 4 lbs/acre or 4 kg/hectare.
Sample Depth
Weight in kg/ha or lbs/acre
1 ppm = kg/ha or lbs/acre
4” or 10 cm
1 333 333
1.33
6” or 15 cm
2 000 000
2.0
8” or 20 cm
2 666 666
2.6
12” or 30 cm
4 000 000
4.0
Converting Phosphate and Potash into Phosphorus and
Potassium
Again mostly in the USA, some labs report Phosphorus as P
2
O
5
, phosphate, and
Potassium as K
2
O, potash. If the lab you are using does this, the conversion to
elemental P and K is:
P
2
O
5
(phosphate) x 0.44 = elemental P (Phosphorus)
K
2
O (potash) x 0.83 = elemental K (Potassium)
In any event, you will want to end up with all of the lab test data on your worksheet
in ppm of the elements tested.
Acres and Hectares
One hectare (abbreviated ha) is 10 000 meters
2
(100m x 100m). 1/100
th
of that is
100 m
2
, an area of measure also known as anAre (pronounced “air”). 100Ares =
1 hectare. This makes the conversion from kg/hectare to kg/Are simple: just move
the decimal point 2 spaces to the left. 120 kg/ha = 1.20 kg/Are. (1Are = 100 m
2
=
1076 sq ft)
The
acre
originated in Europe as
the area one man could plow with a team of
oxen in a day
. This was measured in chains (a chain is 22 yards or 66 ft long).An
acre was (is) defined as an area 1 chain wide and 10 chains long, 22 yards x 220
yards.
1 acre = 66 ft x 660 ft. = 43 560 ft
2
.
An acre (abbreviated ac) is about 40% of a hectare - slightly smaller than an
American football field, which is 50 yards x 100 yards (45 000 ft
2
). The countries
that presently use the acre include the United States,Australia, India, Pakistan,
