Agriculture Reference
In-Depth Information
with parts per million, and 100 grams is 1/10
th
of 1 kilogram, we multiply the above
numbers x 10 to get mg/kg or ppm:
1 meq (or cmol
c
/kg) =
10 ppm Hydrogen H+
200 ppm Calcium Ca++
120 ppm Magnesium Mg++
390 ppm Potassium K+
230 ppm Sodium Na+
To convert these numbers to kg/ha or lbs/acre, multiply by 2:
200 ppm = 400 kg/hectare or 400 lbs/acre
So how do we put this information to use?
Let's say we have a soil with a CEC of 1meq. This is a normal soil, not sandy or
high in clay. We decide that we wish to end up with 65% of the exchange sites filled
with Calcium and 15% with Magnesium,Albrecht's optimum ratio. We know from
above that 200 ppm of Calcium will fill 100% of the exchange sites. We want only
65% filled with Ca, so
200 x 0.65 = 130 ppm Ca
We want 15% base saturation of Magnesium, and know from above that 120 ppm
Mg will saturate 100%
120 x 0.15 = 18 ppm Mg
130 ppm of Ca and 18 ppm of Mg will give us the 65:15 ratio, on a soil with a CEC
of 1.
How about the “ideal” ratio mentioned above, 68% Ca, 12% Mg, 4% K, and 1.5%
Na?
Still working with a soil where CEC = 1:
Calcium: 200 ppm x 0.68 = 136 ppm
Magnesium: 120 ppm x 0.12 = 14.4 ppm
Potassium: 390 ppm x 0.04 = 15.6 ppm
Sodium: 230 ppm x 0.015 = 3.45 ppm
