From coast to coast the pH and nutrient characteristics of our
soils vary greatly. The ability of the soil to provide nutrition to
a plant is critical to the overall health of a plant. When a
soil is unable to provide nutrients in the proper amounts, it can
lead to reduced plant vigor and increased susceptibility to damage
from disease, insects, drought and other conditions.
Routine soil testing is a great tool to help point out nutrient
deficiencies and surpluses, soil pH, and Cation Exchange Capacity
(CEC). Understanding the test results allows for the
selection of the appropriate fertilizer or amendments to help
correct deficiencies and other problems to optimize the uptake of
fertilizer nutrients by the plant. Optimum nutrient uptake is
critical as lost fertilizer nutrients due to lack of uptake equates
to lost dollars.
Soil pH
Optimum soil pH is species dependent, but generally speaking,
turfgrass, shrub and flower nutrient uptake is maximized when soil
pH is between 6.0 and 7.0. Most soil nutrients are readily
available when the soil pH is 6.5. If pH drops below 6.0 and
soils are more acidic, elements like manganese and aluminum become
more soluble and their excessive uptake can reach toxic levels
causing plant stress and failure.
Conversely, high pH or highly alkaline soils usually suffer from
reduced nutrient, and especially micronutrient lock-up (iron,
magnesium and calcium). They can have high concentrations of
sodium resulting in poor soil structure. Water and essential
nutrients don't easily penetrate poorly structured soils, resulting
in nutrient deficiencies and stunted plant growth.
Changing Soil pH
Soil pH is typically lowered with sulfur and raised with
lime. Pelletized lime is generally the preferred method of
lime application over granular for raising pH as it is much easier
to apply, pellets break down with water, are less dusty and
pelletized lime changes the pH quicker than granular lime.
Dolomitic or calcitic lime may be used depending on the soils need
for magnesium or calcium.
In many Western states and certain pockets of the U.S., soil pH
may be greater than 7.5 and may need to be lowered using
sulfur. The amount of sulfur to be used should be based on
the soil test as soil type as well as soils that contain high
amounts of free calcium carbonate aka "free lime" will require
greater amounts of sulfur to lower pH.
Proper Sampling
Soil test results are only as good as the samples collected and
sent to the lab for analysis. Improper sampling is the
largest area for error in the soil testing process and can lead to
test results that could recommend over- or under application of
nutrients and amendments.
Make sure to collect a representative sample of each area being
tested. 1-2 cups of soil are needed for proper testing and
should be free of plant tissue, thatch, mulch or other surface
debris. For areas up to 10,000 sq. ft., 10-12 individual
cores should be randomly taken and combined to make one composite
sample to be placed in a sample bag. For areas over 10,000
sq. ft., randomly take one extra core for each additional 1,000 sq.
ft.
Separate samples should be collected from areas that differ in
soil color, soil texture, and type of plants grown. Avoid
areas that have recently been fertilized or amended. Turf
should be sampled at a depth of 3" below the thatch layer, while
trees, shrubs and ornamentals should be sampled to a depth of 6-12"
with cores being taken from inside and just outside the drip
line.
Benefits of Soil Testing
Soil testing is an agronomic Best Management Practice (BMP)
recommended by the fertilizer industry, university agronomists and
independent consultants that provides many benefits to the
turf/landscape manager including:
• Monitors pH and nutrient levels in turf and landscape
soils
• Offers corrective action to optimize nutrient uptake
(reduce lost fertilizer $$ from nutrient lock-up)
• Aids in customization of fertility programs
• Promotes good industry stewardship
• Allows you to grow a healthy and flourishing landscape to
put your stamp on!
