# Lab Testing and Amendment Recommendation Calculations (PPM, gm/cubic cm, kg / cubic yard)

#### GlueSniffer

##### Member
I sent soil to Logan Labs for testing. My Ca is Low, and Mg, Na, Cl, and Al seem high.
TEC = 14.9
pH = 6.4
55% Organic Matter
Media Density = 0.23 grams per cubic cm
Ca = about 3000 lbs per acre (1500 ppm)
Ca Base Saturation is 48%

I'm trying to play agronomist. What is the calculation to find out how much Gypsum I need to raise ppm of Ca from 1500 to 3500 ppm for 1 cubic yard of soil. I think I know how to calculate it, but unsure which method to determine mass of soil.

Logan reports my Potting Media Density as 0.23 grams per cubic cm. I assume this is dried. When I measure my actual mix (as is - slightly damp with aeration and all still up in there) I get a number closer to 0.45 grams per cubic cm. This makes a huge difference when trying to calculate the mass of one cubic yard of mix.

If I use the media density from the Lab
0.23 grams per cubic cm
764,555 cubic cm per cubic yard
453.6 grams per pound
2.2 pounds per kg
0.23 x 764,555 /453.6 / 2.2 =
0.23 x 766.15
176.2 kg per cubic yard = media density reported by Logan Labs

If I measure the mass of a cup of damp, un-screened soil
One cup measures an average of 106 grams
1000 gm per kg
3231.58 cups per cubic yard
106 gm / 1000 = 0.106 kg
0.106 x 3231.58 =
342.55 kg / cubic yard = media density measured by me

Now I want to raise Ca by 2000 ppm (from 1500 to 3500 ppm).

1ppm = 0.00 1g/kg

If I use my measured density...
(2000 / 1000) * 342.55 kg / cubic yard = 685.1 grams of Ca
Gypsum is 23% Calcium, so I need 685.1 / 0.23 = 2978.7 grams of Gypsum per cubic yard. - using my density measurement

If I use Logan Labs density....
(2000 / 1000) * 176.2 kg / cubic yard = 352.4 grams of Ca
Gypsum is 23% Ca, so I need 352.4 / 0.23 = 1532.2 grams of Gypsum per cubic yard. - using Logan Labs density measurement

I suppose the smart thing to do would be to apply the smaller amount then send another sample back to the lab for testing.

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