Why Soil Tests Are Important?

I’m not sure what it is, but for a significant portion of us there seems to be one thing we overlook in our beginning gardening years: the soil test! I will admit I was guilty of it too- I think I was a few years into my veggie garden until I got one. In fact— I think it was taking the Master Gardener Certification Class that finally kicked me into gear to get one.

So that said- Today I’d like to talk about why soil tests are so important with a few anecdotes from my farming/gardening experience.

To begin we are going to talk about sweet peas- my favorite crop after dahlias. I’ve had an issue with bud drop (stems suddenly losing every bud they have) every year since I started growing sweet peas. Some people say this is environmental, some say it’s nutritional. I was talking to an experienced farmer friend this past spring and he suggested getting a soil test done and then having a custom fertilizer blend made just for the sweet pea crop area.

What a great idea I thought! I contacted a fertilizer company who makes custom blends (Seven Springs Farm Supply) and asked what they needed. They just told me to get a soil test and then call them to discuss what my goals were for the crop.

So off to the Sweet Pea Palace (as we call that tunnel) I go and I gather my soil, put in a bag and mail it off to my local extension service (Clemson University) and then I wait. About a week later I got the results back.

And to be honest, I was a bit disappointed. I was actually hoping the soil was going to be deficient in something. Because solving the bud drop issue in sweet peas from a nutritional standpoint would be a whole lot easier than a climate issue.

But as you can see from the above picture, the soil is great! Boron is an element that is suggested to help with bud drop but there’s no issue with that in my soil.

So back to the drawing board on solving my problem— BUT do you see how the soil test helped me? It helped me eliminate a solution. It also saved me money on fertilizer that I didn’t need. It also tells me that most likely I don’t need to add anything to this soil this fall. I will test it again in September before we plant. But as long as we monitor the elements in the sufficient range from year to year, we don’t need a lot of the typical fertilizer elements you would apply.

Now let’s take a look at a plot of soil over the course of 8 years.

The first soil test I can find for my farm is from Fall of 2016. We moved here in Fall of 2015 but you know how moving goes- I probably forgot to take one when I began.

What you see here is pretty typical for soils in my region. Acidic and high in Potassium and Phosphorus and reasonably sufficient in other elements. It’s clay soil - heavy but rich.

Let’s skip ahead 2 years. This is 2018- same area of soil on the farm.

One noticeable change is the pH- it has gone way up to 7.1 which is actually a little high for what I want. So we used elemental sulphur to bring the pH into a more neutral range. You can also see that the majority of the primary nutrient levels have increased.

In the early years of our farm, we used compost made by our pigs. And it’s great stuff— but it’s rich— richer than our clay soil rich! So after seeing excessive levels for a few years, we backed off of adding the pig compost and any extra potassium and phosphorus.

The cation exchange capacity more than doubled too. If you want more info on what this is- click here. Clemson’s site can explain it way better than I can.

Skipping forward to 2021:

So you can see that we were able to lower the pH level— which changing pH can take some time and it’s a good idea to not make huge adjustments in it quickly.

But the biggest difference is the potassium level is much lower. In fact on all the soil tests we took in 2021- most of them showed a lower potassium level, some even showed that we needed to add. This is a good illustration of how long it can take for a nutrient to adjust in your soil.

Building good soil is a continuous process. You need to have goals but they will change as your soil adjusts.

Skipping forward one more year to 2022:

So what’s different? Well the pH went back up. My guess is because we gave that tunnel a good dose of compost. One thing we work on in our soil is organic matter. Organic matter greatly improves clay soil We don’t always need tons of nutrients because clay soils are usually rich but we need as much organic matter as we can get! So adding compost is something we do on a regular basis. Every year? Nope— too expensive to do the whole farm but we rotate around so that every area gets it every 2-3 years. That decision is crop dependent as well. Adding compost raises your pH level.

The potassium levels have risen- we added muriate of potash. This was in rock salt form and I was able to find it at my local feed and seed.

So what’s the lesson here: Taking regular soil tests gives you so much information to make decisions over time. You can really get to know the soil in a certain area. I’m sure an agronomist could have all kinds of fun with these. That’s way out of my skillset but you don’t have to be a soil scientist to read a basic soil test.

Few other things:
1. These are basic soil tests- there are labs where you can get more in-depth analysis done. You can also pay a bit more on these basic ones and find out your organic matter percentage and the nitrate nitrogen levels (we did this for the Sweet Pea test up top).
2. Where you sending your soil test? Begin by googling your local extension service or your state’s best ag university. Or you can send it to Clemson- they will test out of state soil.
3. How often should I take a soil test? Yearly at a minimum. If you are monitoring a change you are making in your soil then I would say every 6 months. Or take one when you need the answer to a question like I did for the sweet peas.
4. If you have a large area of land, take multiple. Divide up your areas and test them separately. We test all our hoop houses separately and then test a few areas in our main field.
5. How do I take a soil test? Go here— Good directions from Clemson. It’s super easy!!

I really hope I’ve convinced you to get a soil test this fall. Fall is a great time to get a soil test done because you can apply any amendments you need and they will do their work over the winter and your Spring soil will be so much better!

So— go put it on your calendar for some time in September to take a soil test!!