Testing your Soil: 4 Types of Soil Tests and Which Lab to Use for Each
If you’re going to take your home garden seriously, you have to test your soil. No matter what you’re growing, soil testing is how you know what to amend your soil with and it’s how you can measure the effectiveness of your amendments.
In this post, we’ll describe 4 types of soil tests and give you a great lab for getting each test done.
1. Soil Biology Test
Lab: Earthfort Labs
Test: Advanced Package
Price: $167
Included: Total/active bacteria, total/active fungi, protozoa and nematodes, pH
Soil biology is a relatively new science and has gained a lot of momentum over the last few decades. Findings show that organisms in the soil like fungi, bacteria, protozoa, and nematodes play a vital role in determining soil characteristics such as soil structure and fertility as well as potential for plant growth.
Some of the methods you can use to ensure you are growing in a healthy, biologically active and balanced soil are:
- Spending more money to get a living soil instead of a cheaper, conventional soil.
- Amending your garden with a compost tea brewed from a compost high in microbial biomass.
- Adding worm castings to improve soil structure.
- Using larger raised beds instead of smaller containers.
But how do you judge the effectiveness of your strategies? How do you know what you are adding to your soil is increasing the beneficial biology and helping your plants reach their highest potential? How do you know that the “living soil” that you forked over $350/yard for is all that it claims to be?
The answer is to get a soil biology test from a reputable lab. You can’t just go to any random person with a microscope and expect to get accurate results.
Earthfort Labs specializes in soil biology and they’ve been in the game since 1996. Their equipment is top of the line, their reporting is very well laid out and comprehensible, and they provide a telephone interpretation for first time testers.
Here is a BioVast Compost soil biology test result from Earthfort Labs.
2. Soil Nutrient Test
Lab: Logan Labs
Test: Complete Plus Extras
Price: $60
Included: pH, organic matter, base saturation, total exchange capacity, Mehlich III extractable sulfur, phosphorous, calcium, magnesium, potassium, sodium, boron, iron, manganese, copper, zinc, aluminum, soluble salts, chloride, bicarbonate, water soluble phosphorous, cobalt, molybdenum, selenium, silicon, electrical conductivity, estimated nitrogen release
Nutrients in the soil are essential for plant growth and reproduction. Yet, in order for plants to maximize nutrient uptake from the soil, the following conditions are ideal:
- The nutrients in the soil need to be in plant available form.
- The soil should contain sufficient organic matter which, when nutrients are absorbed into the organic matter, will create a reservoir of plant available nutrients. Microorganisms will decompose the organic matter and replenish the nutrient reservoir.
- Your saturation percentages of base cations must be within specified limits. If they are out of range, you most likely will be dealing with nutrient lockout. The ideal ranges for base saturation on a standard soil test from Logan Labs are:
- Calcium (60 to 70%)
- Magnesium (10 to 20%)
- Potassium (2 to 5%)
- Sodium (.5 to 3%)
- Exchangeable Hydrogen (10 to 15%)
- Your pH should be in range; most plants thrive in soil with a pH of about 6.5, but you’ll need to do some research to see what pH you need for what you’re growing specifically.
To find out if the minerals in your current growing media are balanced, you should submit a soil sample to Logan Labs.
Logan Labs has a turnaround time of 3-5 days and their website has well laid out instructions on how to collect and send your soil sample. The staff is knowledgeable and accessible.
If you're interested in learning more about balancing the nutrients in your soil, Bill McKibben, one of Logan Lab’s consulting agronomists, has written two great books; The Art of Balancing Soil Nutrients and A Grower’s Guide for Balancing Soils.
3. Heavy Metals Test
Lab: Midwest Laboratories
Test: Heavy Metals Test
Price: $130
Included: arsenic, cadmium, cobalt, copper, lead, mercury, molybdenum, nickel, selenium, zinc, percent solids
An improper amount of heavy metals in your soil can be toxic, so getting a heavy metals test is a good idea for any grower. Yet, this is especially true for licensed cannabis growers in California; they are required to test for heavy metal contaminants in products intended for retail sale.
Due to their inclusion on the FDA’s Class 1 Category, the following four heavy metals are of key interest when testing:
- cadmium
- arsenic
- lead
- mercury
To avoid failing a heavy metals test on crops meant for retail sale or to make sure your homegrown food or medicine is safe to consume, request a copy of a heavy metals test results every time you purchase a new soil or compost.
If you’d like to get a heavy metals test on your current growing media, try Midwest Laboratories. They’ve been in operation since 1975 and extend their service across the Agriculture, Nutrient Management, Pet Food, Animal Feed, Environmental, Food and Beverage, and Fuel Industries.
Here is a BioVast Compost heavy metals test result from Midwest Laboratories.
4. On-Site Microbial Biomass Test
Lab: microBIOMETER® from Prolific Earth Sciences
Test: 20-minute on-site soil test
Price: $135 for the microBIOMETER® 10 Test Starter Kit; $10 per each additional test
Included: microbial biomass, fungal to bacterial ratio
Let’s say you like to amend your soil. Whether you’re amending with compost teas, compost extracts, Korean Natural Farming inputs, or any other amendment; although it would be helpful to test after each amendment, getting a soil biology test every time you make an addition to your soil could get extremely expensive.
The microBIOMETER® from Prolific Earth Sciences is a cost effective tool that allows you to quickly determine the health of your soil on-site; this allows you to test more often.
The microBIOMETER® was created by:
- Dr. Judith Fitzpatrick - background in microbiology, medical diagnostic test development, and manufacturing.
- James Sotillo - early adopter of regenerative landscaping practices.
- Dr. Brady Trexler - a neurophysiologist.
If you need to get a report on nematodes, protozoa, ciliates, or other microorganisms, you’ll need a soil biology test from Earthfort Labs, but if total microbial biomass and fungal to bacterial ratio are the only results you need to see, microBIOMETER® is a great option.
Here’s what you’ll need to perform your own microbial test:
- microBIOMETER® Starter Kit
- Smartphone (iPhone or Android)
- microBIOMETER® app
