Agriculture Reference
In-Depth Information
Chapter 4
The Primary Anions
Phosphorus P, Sulfur S, and Chlorine Cl
In chapter 3 we looked at some soil test results and calculated how much of the
various
primary cation
nutrients needed to be added to the soil to bring the base
saturation level to our ideal soil balance of 68% Ca, 12% Mg, 4% K, and 1.5% Na.
In this chapter we will learn to calculate the required amounts of the
primary
anions
Sulfur, Phosphorus, and Chlorine
Here is what we calculated for the Ideal Soil ratio of cations in chapter 3:
Total of Major Cations after Balancing
Calcium
Magnesium
Potassium
Sodium
1550 ppm
164 ppm
178 ppm
39 ppm
All of the rest of our calculations for the soil mineral prescription will be based on
these numbers.
Phosphorus P and Potassium
Here is the Phosphorus section of the Ideal Soil chart:
Other major nutrients
(anions)
Phosphorus P- min 100 ppm
P =
Ideal
K by weight (ppm)
BUT: phosphate
(P
2
0
5
) should
be ~
2X potash (
K
2
O)
Needs a highly bio-active soil to
keep it available.
The chart says that Potassium and Phosphorus should be equal by weight in the
soil. If we are going to end up with 178 ppm of Potassium; we want to end up with
178 ppm of Phosphorus too. This gets a little tricky for a couple of reasons:
•
On a fertilizer label in the USAand some other countries, the letters N, P,
and K do not stand for Nitrogen, Phosphorus, and Potassium. They stand
for Nitrogen, phosphate, and potash. N is elemental Nitrogen, but
phosphate is P
2
O
5
, 2 atoms of Phosphorus and 5 atoms of Oxygen. Potash
is K
2
O, 2 atoms of Potassium and 1 atom of Oxygen. More on this below,
but in effect the P on the fertilizer label is only 44% Phosphorus by weight,
while the K on the fertilizer label is 83% Potassium by weight. There is
almost twice as much Potassium by weight in potash as there is
