Soil: TESTING & MANAGEMENT
The Soil Tests and The Nutrients Involved
Brian Jervis, Tulsa County Horticulturist
The Soil Test
Soil tests will help you develop and maintain a more productive soil by providing
information about the fertility status of your soil. Information from a soil test will help
you select the proper liming and fertilization program to obtain optimal growth of lawn,
garden and ornamental plants. BUT, a soil test will not be a magical cure-all. Think
of it as a blood test. When you are sick and go to the doctor, the doctor does not always draw
blood right away. He or she will try to rule out any obvious possibilities that your illness
can be. We need to look at plants the same way. Most soils are fairly stable and will
hold their nutrients with some exceptions. This article will explain how to take a soil
sample correctly and also will give you examples of some of the nutrient deficiencies of
plants. Again you need to assess your problem and overall goals and then make a
decision on weather or not to take a soil sample.
A Representative Sample
One of the most important steps in soil testing is collecting the sample. Soil test results
can be no better than the sample submitted to the laboratory for analysis. A soil sample
weighing about one pound is used to represent thousands of pounds of soil in the
landscape or garden. Therefore, it is extremely important that soil samples be properly
and carefully taken.
The area included in the sample should have been uniformly fertilized and limed in the
past. But DO NOT take a sample if the area has been fertilized or limed in the
past two months. This is very important in getting a representative sample, even a small
piece of fertilizer will throw off your sample and you will be wasting your money. When
collecting the sample, avoid small areas where the soil conditions are obviously different
from those in the rest of the area -- for example, wet spots, areas where wood piles have
been burned, old building sites, fence rows, fertilizer bands, eroded areas and areas
immediately adjacent to roads. If a field contains more than one soil type, collect separate
samples from each soil area. Sample problem areas within a field separately. Again your
soil sample weighing about one pound is used to represent thousands of pounds of soil in
the landscape or garden. For the sample to be representative of the area tested, follow
these steps for sampling:
- Remove any surface litter such as turf thatch or mulch.
- For lawns, sample to a depth of 4 inches. For gardens, ornamentals and fruit trees
sample to a depth of 6 inches.
- Use a trowel or sampling tube to collect soil samples.
- Place the cores in a clean plastic bucket or other non-metal container and thoroughly
mix the soil. Note: Do not use a galvanized bucket for collecting samples, especially
if the soil will be analyzed for zinc or other micronutrients. Ensure that buckets and
sampling tools are clean and free of fertilizer and limestone residues. Even a small
amount of fertilizer transferred from the sampling tools to the soil can seriously
contaminate the sample and produce misleading results.
- Bring the soil sample to the the Tulsa County Extension Office at 4116 E. 15th
Street at gate 6 of the Fair Grounds for processing.
Turn-around time varies with the season but is usually 14 days or less. The standard test
includes soil reaction pH, Nitrogen (N), Phosphorus (P), Potassium (K). The secondary
and micronutrients can also be tested if specified. (See Nutrients Below)
The cost of your soil sample will vary depending on which type you choose. The Routine
Sample is adequate for most home lawn and/or garden and the cost is $10. This test will
include pH, Nitrate-Nitrogen, available P, and available K. For a complete list of prices
go to the Soil, Water & Forage Analytical Laboratory
When and How Often Should Soils Be Tested?
Soil can be tested any time during the year; however, be sure to sample well in advance
of planting or spring green-up. This is particularly important in areas where lime is likely
to be needed. Lime reacts fairly slowly and should be mixed with the soil several weeks
before planting. Generally, fall is the most desirable time to sample soil, because
landscapes and gardens are usually dry and easily accessible. Soil should be dry enough
to till when sampling. If wet samples are collected, they should be air dried before being
placed in the soil sample bag. Once medium or high fertility levels are established, lawn
and ornamental areas only need to be sampled every two to three years. Vegetable
gardens should be sampled every one to two years.
Plants require a total of 16 elements in differing quantities to grow and mature properly.
Three of the 16, carbon, hydrogen and oxygen, make up about 95% of the plant and are
supplied by air and water. The remaining 13 must be supplied to the plant by the soil
solution. These nutrients are grouped according to plant usage -- primary, secondary, and
micronutrients. The primary group, which is the group that is used most by the plant has
three nutrients, Nitrogen (N), Phosphorous (P), and Potassium (K). All commercial
fertilizer is sold must have the exact amount of N, P, & K listedon the bag. When there is
a nutrient deficiency present it is more-than-likely going to be one of these three. The
secondary group includes Calcium (Ca), Magnesium (Mg), and Sulfur (S). The third
grouping is the micronutrients or trace elements, those used in minute amounts. This
group includes Zinc (Zn), Iron (Fe), Manganese (Mn), Copper (Cu), Boron (B), Chlorine
(Cl), and Molybdenum (Mo). Click on the fertilizer bag to the left to see the guaranteed
analysis for that bag of fertilizer.
The pH Factor
Soil reaction (pH) is a measure of the acidity/alkalinity of the soil. On the pH scale 7.0 is
neutral, less than 7.0 is acidic and above 7.0 is alkaline. The major influence of pH is on
nutrient availability. Most plant nutrients, particularly phosphorous, are most available in
mildly acid soils, i.e. those with a pH between 6.0 and 7.0. Agricultural soils tend to
become more acidic overtime. Excess acidity is corrected through application of lime to
the soil. Click here to see the pH Primer"
Overall decreased vigor and light green foliage color. Symptoms begin in older
foliage. All converts to nitrate which can leach from the soil. Ammonium held to
soil. Plants use mostly nitrate, some ammonium.
Leaves dark green to blue-green with petioles and lower leaf surfaces becoming
reddish-purple, eventually yellow. Easily tied up by soil and made unavailable to
plants. Availability reduced at high or low pH and soil temperature below 50? F.
Form for plant use varies with soil pH.
Marginal yellowing of older leaves, then scorching and leaf drop. Mimics
Death of shoot tips, yellowing necrosis of younger leaves, leaf distortion, not
common. Major component of the cell wall. Deficiency related to blossom end
rot of tomato and others. Can be deficient in acid soils, but easily corrected by
Chlorosis and necrosis in interveinal areas. This element is a component of
chlorophyll. Deficiency may show on sandy acid soils. Corrected by adding
Light-green or yellowing starting with the newer leaves progressing downward.
Sulfur is often a contaminant in fertilizer.
Leaves appear scorched and rosetted, stem die back often occurs.
Required by the plant but seldom deficient, symptoms, which include marginal
and tip scorch, occur in toxic levels.
Death of young shoots and leaf scorching.
Deficiencies are apparent when pH is high in the soils. Interveinal chlorosis while
the veins stay green.
Interveinal chlorosis of young leaves beginning at the leaf margins and
progressing toward the midrib.
Seldom deficient, marginal then interveinal chlorosis in middle and older leaves
that may be cupped shape. Essential for N fixation by legumes.
Leaves are yellow to bronze, narrow and rosetted due to short internodes.
Terminal growth areas affected first. Deficiency can be caused by excess