Wednesday, February 22, 2017

I Can Do Soil Science, Me!

I've never really done such a thing before but I figured a soil test wouldn't hurt. For one, it might shed light on why my garden hasn't been living up to my expectations. It also just gives me something garden-y to do while it's still too early to really do much planting. So I watched a few YouTube videos and picked up a test kit at the home improvement store.

First step was to gather some soil (chosen from the center of the bed and about 4 inches below mulch level) to soak in a jar with filtered water overnight.

As per the kit's instructions, this was for the NPK test but it also gave me an opportunity to check the soil texture ratio while it was in the jar. The ruler shows that my soil had (roughly and from bottom to top) 15 mm of sand, 3 mm of silt, 2 mm of clay, and floating at the top 10 mm of peat. So mostly sand, which is no surprise given my geography, even though the bed was filled with 100% municipal "compost".

 Here are those measurements, charted out to easily visualize ratios and then plotted on a soil texture triangle. Solidly in the "Sandy Loam" category but at least there's some loam!

The next step was drawing the liquid from the jar and using it to test for nitrogen, phosphorous, and potassium levels. Those 3 tubes on the right should be bright magenta, deep blue, and a rusty orange. The orange, at least, is clearly present. Plenty of potash. The blue, indicating potassium, is there, if faintly. Nitrogen is very much lacking, as you can see from the sickly pink. Are these tests highly accurate? Probably not but it gives me a ballpark.

Last, with a bit of soil reserved from the jar, I tested the PH balance. The result, a rather rich blue-green, looks pretty alkaline. There is limestone in the area so this is possible. Or it could be a procedural error on my part. The jar I collected into had been full of sauerkraut. Fearing that residual vinegar would give me a false acidic result, I used a fair bit of baking soda when I washed it out. I tried to rinse it thoroughly but there's still some doubt. Clearly I should to run a few more tests.

However, assuming my results were more or less accurate, where does that leave me? Sandy, alkaline soil that's lacking in nitrogen and phosphorous. I my sandy soil is usable, it just won't hold on onto nutrients as well as might be hoped. If the alkalinity is due to limestone, I could adjust it with sulfur but it would swing back eventually, requiring continual amendment. Nitrogen and phosphorous levels can be fixed with fertilizer but, due to the sand content, would need constant re application. Or I just accept my soil for what it s and plant things that prefer alkaline sand.

Or I continue laying on as much good compost as I can make with a lot of chicken manure. Which is what I would have done anyway if I had never done the tests. My garden will probably never be the best ever but over the years the soil will improve. Maybe I'll try a ground cover that is a nitrogen fixer, like clover. I kinda wanted to do that anyway.

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