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Hi Jaclyn,
Normally on the lower CEC soils I try to work out how much of specific cations I can apply. On heavier soils I don’t worry too much about that.
So I don’t know if it’s correct to do it like this, since I haven’t seen it done in scientific papers. But if you have a CEC of 2 cmolc/kg and you want to balance the soil (like maybe an Albrecht system) I always try to work out the amount of elements I should add to balance it.
So if you have 2 cmolc/kg of soil and you want 70 % of the CEC to be occupied by Ca:
2 x 70 % = 1.4 x 200 = 280 mg/kg of Ca in soil.
You then need the density of the soil (fine sandy soil is about 1500 kg/m3)280 mg Ca/kg (soil) x 1500 kg (soil)/m3 = 0,42 kg Ca/m3
You then just take the depth of the soil sample multiplied by the area.So if we took a 20 cm (0,20 m) sample to represent a hectare (10 000 m2) it would then be:
0,42 kg Ca/m3 x (0,2 x 10 000) = 840 kg of Ca to get a base saturation of 70% in the first 20 cm of soil.
I would then take the soil sample and do the exact same calculation to see how many kg of Ca is already in the soil and subtract the 2 numbers from each other, to get a kg of Ca needed to achieve the 70% (for example). I do this just to give me a ballpark figure so I don’t overwhelm the CEC, and also to balance the soil a bit if you want to do the Albrecht system.
On the more sandy soils normally I don’t worry about balancing the cations, I normally just try to make sure that there is enough elements in the soil (ppm) for the plants.
I don’t know if any one else does the calculation like this, so please take if with a lot of salt. Maybe @BrianDougherty or @john.kempf can also give an opinion here.