The Soil Test Guide

The Soil Test Summary
What: The testing of soil for nutrients and related conditions to maximize plant growth and crop productivity.
Who: Soil testing is important to anyone involved in growing plants, from a large commercial crop grower to the casual home gardener.
Where: Soil tests can be made on any soil samples.
When: Soil sampling is usually made on existing plots every two to three years, however, a new plot should be tested once the soil is tillable, i.e. not frozen.
How: Soil testing can be performed either by a consumer testing kit or by contracting with a professional soil testing agency, such as the local county extension office or the nearest land grant university.
Type: Soil tests are available to determine a variety of soil nutrients and physical conditions. These soil tests can be either purchased as a kit for the consumer or a consumer can contact a local soil testing laboratory to have the soil analysis performed.
Why: Soil testing gives a grower the information to accurately amend the soil for maximum plant growth or crop production.
Time: Varies.
Language: N/A
Preparation: The only preparation for soil testing is that the soil must be tillable (not frozen) and that clean collection equipment must be used to prevent contamination, thus ensuring an accurate result.
Cost: The cost of soil testing varies, from a few dollars for a simple soil pH test to several hundred dollars for complex soil testing or for a professional soil testing kit.

By Mary Kay Radnich, Tests.com Contributing Writer

Whether one is a commercial farmer or only concerned about having a lush, green lawn, the fertility or quality of the soil can make or break any gardening venture. The success and productivity of any crop is directly related to the fertility of the soil as required by a given crop. Soil testing is the primary method by which all growers analyze and amend their soil to ensure optimal growth and crop production.

Types of Soil Tests

Soil tests fall into two general categories – those required to test soil nutrients and conditions to ensure optimum growth and those tests which are useful for understanding the capability of soil for engineering purposes, known as the field of foundation engineering.

Nutritional soil testing typically includes, but is not limited to, testing for elements such as potassium, phosphorus, calcium, magnesium, iron, zinc and manganese, as well as soluble salts and nitrates. Other physical conditions of the soil can also be measured, such as pH factor, base saturation, lime requirement index, electrical conductivity, soil organic matter, moisture content and contaminants such as benzene and other petroleum by-products.

Many of the basic soil tests, such as pH and essential plant nutrients, can be performed by the consumer by purchasing a soil testing kit from any garden supply. However, such tests and more extensive testing are usually performed by county agricultural agents or land-grant universities for a fee. Growers can obtain advice from these facilities with regards to amending the soil for a given crop. Individuals can purchase test kits similar to those used by professional agents, if desired. Be sure to check our directory for specific information regarding the purchase of soil tests.

How Soil Tests Work

The most important aspect of soil testing is that the sample be obtained using clean collection implements, such as a soil auger or probe, spade or other sampling tool. Testers must also ensure that the storage device, such as a pail or bin, is also clean. Tools should be washed between sample collections to prevent cross-contamination and preserve the accuracy of the results. Testers should prepare a map of the plot and indicate the testing sites, along with annual plant productivity, which can be invaluable in tracking and predicting the nutritional needs of soil.

Soil samples should be taken once the soil is workable. First, testers should remove any debris from the top of the soil, or in the case of lawns, remove the turf thatch. While lawns should be sampled at a depth of 3”, an orchard, flower bed or home landscaping should be sampled at a depth of 6-8”. Crop fields or gardens should be sampled between the rows to avoid concentrated bands of fertilizer. Any soil that is distinguishable by color or any fields with a differing fertilizer schedule should be sampled separately.

Air dry the sample (do not use a heat source) and then crush any lumps to the size of wheat grains. If an outside lab is used, the instructions should be followed for labeling and sending the samples in for analysis.

Preparation for Testing

In preparation for testing, a gardener should first create a simple map of the field, garden or lawn to be tested. Clean tools should be used to collect soil samples at the correct depth from various places in the plot. Sampling sites should be marked on the map. Soil testers should follow the instructions from either the test kit or soil analysis lab, then dry the sample and prepare it for testing or mailing to the lab.

Soil testing need only be done every two or three years unless there is a problem with plant growth, disease or crop production.

It is imperative that proper soil sampling techniques are used to ensure accurate results. Contamination of a soil sample will result in an inaccurate analysis leading to improper amendment of the soil.

Are you seeking to amend your soil to increase plant or crop production? Looking for a lush, green lawn? Why not consult our Soil Test Directory to fulfill your soil testing needs? For more on soil testing, please look at our interviews with soil testing experts Stephanie Murphy, Dawn Pettinelli and Jonathan Dahl.