Soil Testing

A soil test is a process by which elements (phosphorus, potassium, calcium, magnesium, sodium, sulfur, manganese, copper and zinc) are chemically removed from the soil and measured for their “plant available” content within the sample. The quantity of available nutrients in the sample determines the amount of fertilizer that is recommended. A soil test also measures soil pH, humic matter and exchangeable acidity. These analyses indicate whether lime is needed and, if so, how much to apply.

SAMPLING PROCEDURE

Soil samples can be taken in the spring or fall for established sites. For new sites, soil samples can be taken anytime when the soil is workable. Most people conduct their soil tests in the spring. However, fall is a preferred time to take soil tests if one suspects a soil pH problem and wants to avoid the spring rush. Fall soil testing will allow you ample time to apply lime to raise the soil pH. Sulfur should be applied in the spring if the soil pH needs to be lowered.

How to take a soil sample?

Most errors in soil testing occur when the sample is taken. Potential sources of errors include the following:

• Too few cores per sample

• Failure to properly divide the area to be sampled • Failure to cover the whole area

• Contaminated sample

Taking a representative sample is important in soil testing. Use a trowel, spade and sampling tube/core samplers.

• For garden and lawn establishment or renovation, take a 6-inch sample.

• For established lawns, take a 3- to 4-inch sample after removing thatch. • Sample from five or more scattered/random spots in the test area.

Standard Soil Tests by AgriGenics

  • AASHTO T290: Sulfate Ion Content in Soil
  • AASHTO T291: Chloride Ion Content in Soil
  • ASTM C1580: Sulfate Ion Content in Soil A
  • STM D1498: Redox Potential of Water A
  • STM D2216: Moisture Content of Soil
  • ASTM D2487: Soil Classification
  • ASTM D421: Dry Prep SOIL SAMPLES
  • ASTM D4318: Liquid Limit, Plastic Limit, Plastic Index of Soil
  • ASTM D422: Particle Size Analysis of Soil
  • ASTM D4972: pH of Soil
  • ASTM G102: Corrosion Rate
  • ASTM G51: pH of Soil for Corrosion
  • ASTM G57: Soil Resistivity
  • ASTM D4658: Sulfide Ion in Water
  • ASTM G162: Conducting and Evaluating Lab Soil Corrosion Tests
  • ASTM D512: Chloride Ion in Water
  • MIC Tests

SOIL TESTING FOR AGRICULTURE

The soil test is an excellent gauge of soil fertility. It is an inexpensive way to maintain good plant health and maximum productivity without polluting the environment by over-application of nutrients.

Soil fertility fluctuates throughout the growing season each year. The quantity and availability of mineral nutrients are altered by the addition of fertilizers, manure, compost, mulch, lime or sulfur and by leaching. Furthermore, large quantities of mineral nutrients are removed from soils as a result of plant growth and development and the harvesting of crops. A soil test will determine the current fertility status. It also provides the information needed to maintain optimum fertility year after year.

Some plants grow well over a wide range of soil pH, while others grow best within a narrow range of pH. Most turf grasses, flowers, ornamental shrubs, vegetables and fruits grow best in slightly acid soils (pH 6.1 to 6.9). Plants such as rhododendron, azalea, pieris, mountain laurel and blueberries require a more acidic soil to grow well. A soil test is the only precise way to determine whether the soil is acidic, neutral or alkaline.

A soil test takes the guesswork out of fertilization and is extremely cost effective. It not only eliminates the expense of unnecessary fertilizers but also eliminates overuse of fertilizers and helps to protect the environment.

Soil Sampling FAQ

Soil samples can be taken in the spring or fall for established sites. For new sites, soil samples can be taken anytime when the soil is workable. Most people conduct their soil tests in the spring. However, fall is a preferred time to take soil tests if one suspects a soil pH problem and wants to avoid the spring rush. Fall soil testing will allow you ample time to apply lime to raise the soil pH. Sulfur should be applied in the spring if the soil pH needs to be lowered.

A soil sample is best taken with a soil probe or an auger. Samples should be collected in a clean plastic pail or box. These tools help ensure an equal amount of soil to a definite depth at the sampling site. However, a spade, knife, or trowel can also be used to take thin slices or sections of soil.

Push the tip of a spade deep into the soil and then cut a 1 ⁄2-inch to 1-inch slice of soil from the back of the hole. Be sure the slice goes 6 inches deep and is fairly even in width and thickness. Place this sample in the pail. Repeat five or six times at different spots over your garden. Thoroughly mix the soil slices in the pail. After mixing thoroughly, take out about 11 ⁄2 cup of soil and mail or, preferably, take it to your University Extension center. You can also mail

or deliver it to the University of Missouri soil testing lab on the University of Missouri campus in Columbia or at the Delta Research Center in Portageville. It is important that you fill out the soil sample information form (Figure 5) completely and submit it with your sample. By indicating on the form the crops you wish to grow, you can get specific recommendations.

Soil should be tested every two to three years. In sandy soils, where rainfall and irrigation rates are high, samples should be taken annually.

In general a regular fertility test is sufficient. This includes measurement of pH, neutralizable acidity (NA), phosphorus, potassium, calcium, magnesium, organic matter (OM) and cation exchange capacity (CEC).

Some labs report soil test values as amounts of available plant nutrients, and others report extractable nutrients that will become available to the plants (Figure 6). Fertilizer rates are given in pounds of actual nutrient (as distinct from pounds of fertilizer) to be applied per 1,000 square feet.

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