A Primer on Soil Testing
What is soil testing and what are the benefits of doing it?
The success of growing crops depends on a few critical factors such as the availability of sunlight and water, temperature changes and the soil condition. Soil health has a direct impact on crop yield and quality. To determine if the soil is in optimal condition, soil samples may be sent to labs in agricultural universities for testing (this test typically costs around $15), where the soil’s pH is tested, along with levels of phosphate, potassium and the presence of other organic matter. However, such tests do not typically test for nitrates, which is an important element for healthy plant growth. For a more detailed analysis (typically costing around $50), commercial labs provide a basic test that would include more detailed results such as pH level, and levels of phosphorus, nitrogen, calcium, potassium, magnesium and other organic matter. For a few dollars more, you may receive results on additional tests done for levels of iron, copper, zinc, and manganese in the soil. If your soil is not in optimal condition, these labs would also provide recommendations on how to improve the soil organically.
What kind of lab should you select for soil testing?
There are many labs out there providing soil testing services, so how should you select a lab among all the options available? When selecting labs, it is recommended to find labs that do base saturation tests such as Reams, Lamotte or Albrecht. Preferably, the lab should be able to provide recommendations that are less damaging to the soil (some labs advocate the use of strong fertilizers such as triple superphosphate and potassium chloride which may be harmful to the soil and do not help create healthy soil in the long run).
How should soil samples be collected?
For accurate test results, it is important to pay attention to the way soil samples are collected. Soil samples should be collected prior to the application of fertilizers and lime, which may skew test results, and sample collection should be done preferably immediately after winter.
If you are testing on a big piece of land with varying terrains, conduct a test for every 5 acres of land. Within the 5 acres, determine 15 spots where samples will be collected and take note of the exact locations, as this information will be needed for tests in future years.
Use a soil probe which can help ensure the samples are collected at the same depth and collect samples from a soil depth of 1 foot. Remove all grass, stones and non-soil items. Then, use a knife to collect soil from the middle (not surface) of the soil column gathered by the soil probe. Do the same for all 15 samples, remembering to crush and homogenize the soil in a plastic bucket.
Fill up a third of the soil bag provided by the lab, or approximately 2 cups if you are using a ziplock bag. Complete the lab’s sample form with all required information and make a copy to be retained together with your information on the coordinates of the soil collection spots, then send the sample and completed form to the lab. Be sure to follow the lab’s recommendation which accompanies the test result, in order to improve your soil quality for your desired crop.