Aug 042011

We live on a former Superfund site, so when I started planting in the garden a few months back, I was worried that there would still be some residual contamination from heavy metals and other deadly chemicals. I sent in a soil sample to the UMass Extension Service for testing, and just got back the results.

The good news is that the dangerous stuff are all pretty low. Trace of lead (30ppm), very low cadmium (0.1ppm), etc.

The interesting parts were actually the nutrients and soil composition. The pH turned out to be 7.5, with nitrates at just 3ppm, and extremely high calcium levels (20187ppm). The soil is buffered at a pH of 7.4, probably because of the high concentration of calcium. What’s also interesting is that the phosphorus levels are very high as well (45 ppm, where 20 is usually considered high). My guess is that the previous residents of this house used lime to fertilize, then applied lots of P-heavy fertilizer when the plants were still doing poorly. Since the calcium from lime ties up the phosphorus, a high P concentration was necessary for the plants to get any. Disturbingly, sulfur levels are just as high, at 356ppm. It’s as if previous residents saw others using sulfur and lime and 10-30-10 fertilizer, and decided that applying all three all the time was the way to go, without knowing what each component did.

This is bothersome, since I want a target pH of 6.6 or so, and how I’ve always lowered the pH has been to add sulfur, or to use an acidic mulch. But is it safe to add more sulfur? With all that calcium, it would seem like I need a lot of it to overcome the buffering at 7.4.

I’m also guessing that the low nitrates is normal; I haven’t fertilized in 3 months, and nitrates are pretty mobile, but should I add more nitrogen, in the form of dried blood or something similar? Because 3 is very low.

Full results:

soil pH: 7.5
Buffered pH: 7.4

Organic Matter: 6.9%
Soil Weight: 5.1g/5cc
Cation Exchange Capacity: 103.3 Meq/100g
% Base saturation: K=1%, Mg=3.3%, Ca=95.9%

Nitrogen (NO3-N): 3 ppm
P: 45 ppm
K: 373 ppm
Ca: 20187 ppm
Mg: 414 ppm

Al: 12 ppm
B: 1.3 ppm
Mn: 11.3 ppm
Zn: 3.7 ppm
Cu: 0.0 ppm
Fe: 0.6 ppm
S: 356 ppm

Extracted Pb: 0.0 ppm
Total Pb: 30 ppm
Cd: 0.1 ppm
Ni: 0.2 ppm
Cr: 0.11 ppm


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