Limestone (calcium carbonate) is a naturally occurring nutrient
vital for healthy soil in rainy zones of western Washington. Whether you own a large farm or a small lawn, lime can play a
big part in higher crop yeilds and lush, green grass.
Raises pH, reducing acidity
Increases efficiency of fertilizers
Helps aerate soil by boosting microorganisms
Stabilizes soil aggregates to slow erosion
Encourages activity of soil bacteria, releasing valuable nutrients from organic
components in the soil
What is Lime?
Common liming agents can be divided into two major types--calcitic and colomitic. Although there are many other materials
available, we will be focusing on the value of calcitic limestone flour, commonly called Aglime. Dolomite is
the name of limestone containing Magnesium Carbonate in combination with Calcium Carbonate. By definition it must contain
a minimum of 30% MgCO3. The primary reason for using a dolomitic liming material is to provide Magnesium for plant uptake.
Dolomitic limes are also much slower to breakdown thereby providing a slow pH rise for crops that may be adversely affected
by a quick change in pH (such as Blueberries).
Calcitic limestone flour is rated by the percentage of CaCO3 contained in the naturally occurring limestone rock that
is ground into a fine powder, or flour. Most of the limestone used in Western Washington is quarried on Texada Island in Brittish
Colombia, Canada. We are fortunate to have large reserves of high quality limestone (97% CaCO3) in close proximity to our
growing region. In order for limestone to be useful for agricultural purposes, it must have large surface areas exposed, hence
the advantage of finely ground limestone flour.
When is Lime Needed?
The Cation Exchange Capacity
is a measure of the quantity of cations that can be absorbed or held by a soil. Clay particles and soil organic matter have
a negative charge. This means that cations or positively charged ions can be attracted to and held on the surface of these
soil materials. A mineral soil with a high CEC tends to be more fertile than that with
a lower CEC. The nutrients are less likely to be leached and the soil has a greater ability
to store and supply nutrients to the plants. The cations of greatest significance are calcium, magnesium, potassium, ammonium,
sodium, and hydrogen. The first four are important plant nutrients, the last two have a pronounced effect on soil chemistry
and physical characteristics. Acid soils have a high percentage of absorbed hydrogen ions while soils with a favorable pH
have a high percentage of absorbed calcium ions. Soils that are high in sodium ions are dispersed and resist the infiltration
of water while those with a high percentage of calcium ions are well aggregated and have high infiltration rates. Calcium
ions will displace sodium ions on the surface of the soil particles.
A pH test is used to determine
if lime is needed, however a lime requirement is needed to determine how much lime to apply. A complete soil test is recommended
to include pH, buffered pH, lime requirement and nutrient levels in the soil. A buffered pH test uses a solution of soluble
calcium in the water used to prepare the soil sample for the pH test, generally a one to one mixture of soil and distilled
water. The change in pH from the sample with distilled water only versus the sample prepared with the buffered solution will
indicate the change that can be expected with the addition of lime to the soil. A large change upward with the buffered solution
will indicate a small amount of lime is needed to raise the pH, while a slight change or downward change will indicate a larger
amount of lime will be needed. In addition, the small amount of calcium present in the soil should be noted.