Why and How to Soil Test — The First Step to Better Soil Health
The first step to better soil health should always begin with a soil test. Every property is different. A good soil health regime should be tailored to your farm’s specific conditions and needs. Hence, why you test your soil!
Soil tests are not expensive, ranging anywhere from $30 to $80 a test depending on what you test for, but it gives you a baseline showing where you started and charts your soil improvements over time. A soil test can reveal critical issues with your soil that you would otherwise take a best guess at.
What Does a Soil Test, Test?
The basic “macro” soil test will tell you the fundamental composition of your soil and give you a good idea of the available nutrients for plants.
It will include basics like your soil PH — how acid or alkaline your soil is. It will tell you what your available nutrient levels are, testing nitrogen, potassium, phosphorous, magnesium, calcium and sulfur. Most soil tests will include your percentage of organic matter, the organic content readily available in your soil that provides nutrients to plants as it breaks down.
Depending on what crops you are growing or if the basic soil test indicates any imbalances, you might want to test your micronutrients. That’s called a “micro” soil test and usually checks for boron, copper, iron, manganese and zinc levels.
Most labs will offer recommended amendments for specific crops based on your soil test and have somebody on staff to answer questions and help you interpret your soil test. Otherwise, there are many resources online to help analyze your soil tests, including this great one from PennState Extension.
Test Your Soil Consistently
Once you get your first soil test done, stay consistent.
Use the same lab. Different labs will present things differently, even use slightly different metrics for measurement, which can make comparing your soil tests from year after year confusing.
Also, test your soil at the same time every year. Many nutrients (especially nitrogen) will test differently depending on how warm the ground is. If you test your soil in the early spring one year (when nitrogen is bound up by cold weather) but then the following year you test in mid-summer (when nitrogen is more plant-available because the ground is warmer), it could lead you to false assumptions about your total nitrogen availability and how your soil health regime has been influencing it.
How Often Should You Test Your Soil?
How often you test your soil will depend on what crops you are growing and, potentially, how closely you want to stay on top of changes in your soil.
If you are starting with a new soil improvement strategy, you might want to test every year for the first few years to chart the results of your efforts. Otherwise, it depends on what you are farming. Generally speaking, agronomists recommend conducting soil tests:
Every two to three years for pastures.
Every two years for hay fields.
Annually (or even twice yearly) for high-value cash crops like specialty vegetables or annual fruits.
Every two to three years for no-till crops.
Every three to five years for perennial crops like orchards or berries.
Any times a nutrient problem is suspected and at the beginning of a different cropping rotation or land use.
Some farms -- especially if they are growing plants that utilize nutrients heavily, like annual vegetables -- will test twice a year. Once in spring to make sure they have enough nutrients to support their planned crop rotations and then in the fall, to see how much available nutrients were left after a season of growing and applying fertilizers. It is expensive and harmful for the environment to overapply nutrients, even when fertilizers are organic. Two tests a year in heavy production systems can help growers know if they applied enough — or overapplied — for their crops and help them adjust future fertilizing regimes.
How to Soil Test
How you take your soil test is critical.
The first step is asking the lab you plan to use what they want you to put the soil test in. Many labs will send you specific bags to package your soil test in.
Also, a soil test can easily be corrupted by dirty equipment or by not taking a good sample. If you’re working closely with an agronomist, they will typically take your sample for you, making the job easy! But most small farms will need to take their own and ship it to the lab.
Tips for taking a quality soil test sample:
Use the right tool and make sure it’s clean when you start. Ideally, you use a soil probe (or auger), but you can use a sharp spade, long knife or trowel. Hint: Oftentimes, your local extension office will have soil probes they lend out to county residents for taking soil tests. Call them and ask!
Take a deep sample, at least 6 to 8 inches. If you’re not using a soil probe (which pulls the same amount of soil every time), make sure you dig up equal amounts at each location.
In large areas (like a field), you’ll want to take 10 to 15 core samples. In smaller areas (like a greenhouse), you’ll need four to six core samples.
Remove surface debris (leaves, thatch, rocks, etc.) before you take the probe.
Dry the samples at room temperature, break up any large clumps of dirt and mix all of them in a bucket to get a homogenous sample that you then pull the final sample you send to the lab.
For more details on how to test your soil, Purdue Extension has a helpful resource linked HERE.
What are You Waiting For?
For a farmer, a healthy, productive soil microbiome is worth its weight in gold. But healthy soil doesn’t happen overnight.
The first step to getting there is knowing where you are starting from. So, what are you waiting for? Get a soil test!
P.S. Wondering WHERE to send your soil for a test? The best place to ask in your local community is your extension office. Almost every single county in the U.S. has an extension office. Call your county offices and ask for your local extension services.
Georgie Smith, known in her community as “Farmer Georgie,” is a fourth-generation farmer and journalist living on her family’s historic farm on a Pacific Northwest island. She ran her own small farm for more than 20 years. These days, when she’s not herding chickens, fixing the antique tractor (again) or growing heirloom dry beans, Georgie writes about farming. Georgie is passionate about supporting healthy, equitable and sustainable food production and thriving family farms.