Tuesday, February 11, 2014

Taking the Soil Test: Did I Pass?

As I’ve mentioned in some of my previous posts, my winter garden hasn’t been much to write home about. My peas grew about 2 inches and then stopped. My broccoli starts grew in an inch or two and then went straight to flower. A lot of the seeds never grew at all. Meh. So I finally decided to do a little digging back there to see what was going wrong.

Who knows? Maybe I’d dig up something interesting while I was at it. 

There are always a lot of possible culprits to an unsuccessful garden, but I decided to start my investigations with a soil analysis. Because I created a new plot with new soil just last year, the soil seemed like the likely culprit. I decided to use two methods: a home soil kit (Rapitest pH Soil Tester) and a professional lab (IAS). I wanted to compare the two, just in case the cheap and easy home test could give me similar results to the more expensive professional lab. 

What I hoped for was that the expensive lab analysis would tell me exactly what my problem was and tell me exactly how to fix it, but also, that the home test would return similar results. That way, I would be able to use the cheap kit in the future and know how to interpret the results from it. More realistically, however, what I expected was that the expensive lab analysis would tell me exactly what my problem was, give me a good idea how to fix it, and the home test kit would be kind of useless.

It actually took me quite a while to figure out what I thought of the results that I got. 

Let's start by looking at the Rapitest results. I picked Rapitest because it is one of the most highly rated home soil test kits on the Internet. To use it, you put some water, a little bit of soil, and some testing solution in the little container. Then you shake it up and see how the color of the water compares to the colors on the test kit. I always find these tests a little frustrating. I have a pretty good eye for color, but they never match the little color swatches exactly, so I'm always kind of guessing where things fall in the range. 

 I hope you're not color blind

What I took away from my test was that my soil is pretty alkaline. How alkaline? I don't know. A lot, I guess. There was some general information that came with the kit as well about adjusting my soil's pH, but I didn't really look at it too closely. I figured if I was going to do that, I would look at some Arizona-specific literature on the subject, not the back of a cheap soil-testing kit.

Next up, the IAS Lab results. These were more in-depth, as expected. There were definitely people with lab coats and magnifying glasses and other gratifyingly geeky equipment who came up with this stuff! And I got a very exact pH measurement from them.


Boron readings? Oh, this is good geekery.

After looking through page 1 of the analysis, which had some very impressive, but very confusing readings for all sorts of minerals, I moved onto page 2, where they gave me their recommendations: 

Oh thank goodness! All those readings translated into English!

For those of you having trouble reading the fine print, it basically boils down to: "Your soil's pretty good, but the nitrogen is really low." That seemed like good news to me, because adding nitrogen is easy. And it made sense why winter garden had done so badly. Nitrogen is one of the main things that plants need. So that seemed like an easy fix. Problem solved!

But something was nagging at me. It was that pH thing. The cheapo Rapitest seemed to indicate that my pH levels were pretty high, and the pro test actually confirmed it. IAS measured my pH levels at 7.7! Didn't I need to do something to correct it? Shouldn't I add some sulfur to the soil to lower the alkalinity? Why hadn't IAS said anything? 

So again I started digging.  And I came across this article in Organic Gardening. Basically, it boils down to this: Lowering your soil's alkalinity (pH) is hard. It takes time. Don't add a bunch of sulfur to soil where you're trying to grow plants. Instead, just keep adding compost each season. Eventually, you'll get there. And try to choose plants that can handle higher alkalinity. Hmm, I can see why IAS didn't say anything about lowering the pH, but it's not quite the "Victory! Problem solved!" feeling I had two paragraphs ago either. 

Overall, I think I've decided my initial hunch was right.  The expensive lab analysis did tell me what my problem was (low nitrogen), gave me a good idea how to fix it (amend the soil), and the home test kit was kind of useless. (Yes, it did tell me about another problem that I have, but it's not a problem I can do a whole lot about, so what's the point?) So my big plan is to give the soil a big shot of nitrogen now by tilling in some soil amendments, and to periodically add fish emulsion to the plants over the course of the season. Hopefully, that will do the trick. 

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