Agriculture Reference
In-Depth Information
atively charged clay particles and humus in the soil to attract and hold pos-
itively charged cations, including calcium, which has two positive charges.
The higher the CEC, the greater the soil's ability to bind to cations. Like-
wise, soils with low CEC values have less binding ability. This is important
because nearly all plant mineral nutrients are positively charged, so as the
CEC increases, so does the soil's ability to bind to and store these nutrients.
Nitrogen, being negatively charged, does not bind to the negatively charged
soil particles. This is one of the reasons that nitrogen is easily lost from the
soil and why it is the nutrient most likely to be deficient in soils.
Soils with low CEC values quickly saturate with cations and have high
nutrient ratings, even when soil tests show low concentrations of those nu-
trients. This apparent contradiction arises because low-CEC soils have rel-
atively few spaces for the nutrient cations to fill. On a low-CEC soil, all of
the sites may be filled with calcium, leading to a high calcium saturation
rating, even though the actual amount of calcium present in the soil is low.
Soils with high CEC values require larger concentrations of calcium to bind
to their available sites, and calcium ratings can be low, even when abund-
CEC and calcium soil test results.
If your soil's calcium rating is low and the pH is 6.5 or above, add gypsum
as a soil amendment up to the time of planting (see the sulfur section above).
Consult with your soil testing lab for recommended amounts of gypsum to
add.
If the soil pH is less than 6.5 and soil magnesium levels are adequate, add
limestone, preferably several months or more before planting your trees. If
the pH is less than 6.5 and magnesium is also deficient, add dolomitic lime-
stone. Remember that pH is an important factor in calcium management.
Keep your soil between pH 6.0 and 7.0 and, ideally, around 6.5. Use the
amounts of limestone or dolomite needed to adjust your soil pH to 6.5.
