I know you’ve been looking forward to another in my gripping Agronomy Series, so you’ll be happy to know that I got my soil test results back from the University of Massachusetts at Amherst lab.
Now that I’m an adult, I don’t take tests very often. Although I’m tested all the time, it’s in the life-hands-you-lemons kind of way, not the please-begin-you-have-one-hour kind of way. So it’s been a while since I opened an envelope with test scores.
Naturally, I wanted to do well. Despite the fact that our property is built on a substance called Carver Coarse Sand, I felt personally invested in the results of the soil test. After all, we’ve been amending for two years now. Had we managed to turn our sand into something resembling nutritious soil?
The envelope, please!
Below are my results, in full.
The reason I’m posting them for all the world to see is that there are some things about them that I don’t understand. I have questions. My experience here at Starving has taught me that you often have answers. So here goes.
Q: Organic Matter. Ours is 11.8%, and the desirable range is 4-8%. Way high, in other words. Did it get this way because we tilled a whole lot of compost into that sand? Once you have too much organic matter, I can’t imagine there’s a way to get it out, so I assume you fix that problem by adding things that aren’t organic matter. It’s like if you oversalt the soup, and you add more stock and vegetables. Is this a problem that will go away of its own accord if we keep amending according to recommendations, and don’t add more compost? But aren’t you supposed to add compost?
Q: Buffer pH. I understand about pH, and that 5.6 is too acidic. Our hoophouse soil probably got this way because we grew potatoes in part of it last year, and mulched them with a mix that was high in pine needles. The recommendation we got was to mix 20 pounds of ground limestone per 100 square feet of garden (the hoophouse is about 150 square feet).
But the explanation included in the result says that buffer pH “is a measure of the soil’s capacity to resist pH change after lime has been added.” It goes on, “The extent to which the buffer pH is lower than 6.8 is proportional to the amount of limestone needed.”
Great. So not only do we have a garden that’s too acidic, we have one that’s resistant to change. Just what I need – pushback from my dirt.
While I understand all the words, I don’t really understand what it means. What makes soil resist having its pH changed?
Q: Cation exchange capacity and base saturation. Per the information that came with my test results, CEC is “an important measure of the soil’s ability to retain and to supply nutrients.” This one had me at a loss until I read this excellent explanation by soil scientist Michael Astera. Now I know, among other things, how to pronounce ‘cation.’ It’s not like a vacation without the va. It’s like the chipmunk who’s blissfully unaware that there’s a ‘cat eye on’ him. (Stupidly, although I know what an anion is and that it isn’t pronounced like companion, I never figured out that cation was the opposite.)
I also understand that the CEC is simply the extent to which your soil can attract positively charged particles. Specifically, those associated with calcium, magnesium, potassium, and sodium. It gets a little more complicated when we start talking about base saturation. I’m not even going to try to figure out whether “saturated” means that all those negatives looking for positives are hooked up. I’m just worrying about the percentages.
The UMass materials say that a balanced soil is 70/12/4 (calcium/magnesium/potassium), and my new favorite soil scientist (everyone should have one!), Michael Astera, says 65/15/4, but adds that these are only rough guidelines.
We’re at 47/13/3, which is clearly low on calcium. Here’s the question – if we amend with limestone, will that solve the calcium problem?
Q: Micronutrients. We’re low on almost all of them, from boron to zinc. The only one we’re anything like rich in is sulfur. While it’s nice to know that we’ve got brimstone, in case we want to add fire and simulate hell, I’m worried about the rest of the micronutrients. Do we correct for them?
Q: Chicken poop. We’ve got a barrel full of beautifully composted chicken poop. I think that should correct our moderate nitrogen deficiency (and we also have phosphate for the phosphorus). But will it help with other things as well? And, since the poop composted in pine shavings, will that make the soil more acidic?
Okay, I’ll stop now. If you have any insights, comments, or, even better, actual answers, I’d very much appreciate them. If this goes well, I’ll think about tackling other fascinating subjects, like the burning potential of various kinds of hardwoods, or the pros and cons of annual bottom painting (those are boat bottoms, for those of you who thought that might not be so dull).
Meanwhile, it’s all soil, all the time.