It isn’t the first time that I was looking at soil, yet the situation was different now. Previous samples were mostly sandy soil or clay, but the ones discussed here were more like peat.
When I was a young boy, I lived in Fryslân (Friesland) for a couple of years. During my recent vacation I visited the forest “Oranjewoud”, where I had been so often back then and of course I took some soil samples. At two locations – a couple of kilometres apart – I collected between five and ten superficial samples (5-15 cm, after scraping off the humus top layer) in a range of ten metres and combined them.
The samples were taken close to the point where we (I took a stroll in the wood together with my youngest son) entered the wood and then close to hotel Tjaarda. The maps below show the locations. Although the coordinates seem very precise, I don’t know the exact locations. It’s just somewhere in neighbourhood of the marker. Although the first marker is closer to another road, I called it “Lollius Ademalaan” because for me that’s a familiar location. The other one is called “Tjaarda” for obvious reasons. I remember the parents of a classmate were the owners or managers of the hotel, but those days are long gone.
At home I spread out the samples on cardboard to dry as usual, but because the soil looked different (lot of peat) I decided to do preliminary measurements at the fresh soil as well. This was mainly to check what the impact of drying would be. By the way, the pH values for the fresh Lollius Adema samples (soil to water 1:1) were 3.24, 3.36 and 3.44 with conductivity 148, 157 and 144. For Tjaarda it was 3.14, 3.23, 3.19 with conductivity 238, 206 and 248.
In the end the pH and conductivity were not very different after drying, but some complications came up.
Because the soil was weighed before and after drying, the water content could be determined. The Lollius Adema sample-set held some peat but was rather sandy and the moist percentage was only 16% (not surprising after a long period of drought with probably two small showers). For Tjaarda however, it was 56% (= 44% of dry stuff) and there is the complication: if a dry sample is mixed with the same weight of (demineralised) water, it still holds less water than the fresh sample! Nevertheless it was possible to determine the pH of something looking more like normal peat rather than slurry. For the conductivity the lack of water is very influential, so for Tjaarda additional measurements were done with soil to water ratios 1:2 and 1:3.
We know that the pH is rather predictable for the dilutions, so the values were only checked once for the two Tjaarda-slurries : 3.60 and 3.70 (really, no rounding!). This is more or less the expected log(2) = 0.3 increase.
Adding additional water will lower the conductivity if the slurry contained enough water already and indeed for Lollius Adema (LA) the conductivity readings for the 1:2 ratio were about half of the previous values (because the water-volume was doubled). The 1:1 LA slurry showed values 268, 280 and 221 for slurry 1 µS/cm and 191, 180 and 202 µS/cm for slurry 2. (The difference shows that it’s hard to get a representative sample for mixed soils.) For the 1:2 LA slurry 1 is was 123 and 155 and for LA slurry 2 is was 95 and 97 (only two values, because it was just a check.
For the Tjaarda peat it was quite different! Adding more water increased the conductivity. It became more of a slurry and the dissolved salts could do their job now. The original 1:1 values for Tjaarda (Tj) “slurry” 1 were 59, 63 and 76 and for “slurry” 2 it was 55, 87 and 63 (be aware that three rounds of measuring are presented for the same slurry, showing that the error is rather large, although the difference between these two slurries was much smaller, because this soil was more homogeneous.
After adding (demineralised, of course) water again, the values were 82 and 119 for slurry 1 and even 261 and 276 for slurry 2. Obviously the soil was less homogeneous than presumed, because the response to additional water was quite different!
Finally the soil to water ratio was increased to 1:3 by adding the same amount of water for the third time (25 grams of soil were now mixed with 75 grams of water). Slurry 1 went up and came close to the LA values now. 229 and 272 – all µS/cm, because that’s our standard unit. Slurry 2 was over the top and went down again: 210 and 214.
For those who like tables or want to calculate averages, standard errors and the like the Tjaarda information is provided in a table.
| Tjaarda | condutivity in µS/cm | ||
| Soil to water ratio in mix: | 1:1 | ||
| “Slurry” 1 | 59 | 63 | 76 |
| “Slurry” 2 | 55 | 87 | 63 |
| Soil to water ratio in mix: | 1:2 | ||
| Slurry 1 | 123 | 155 | |
| Slurry 2 | 95 | 97 | |
| Soil to water ratio in mix: | 1:3 | ||
| Slurry 1 | 82 | 119 | |
| Slurry 2 | 261 | 276 |
To be more complete, a table of the pH measurements before and after drying (only for the 1:1 soil to water ratio) is added below for both locations.
| Lollius Adema | pH before drying | ||
| Soil to water ratio in mix: | 1:1 | ||
| One slurry | 3,24 | 3,36 | 3,44 |
| Lollius Adema | pH after drying | ||
| Soil to water ratio in mix: | 1:1 | ||
| Slurry 1 | 3,43 | 3,44 | 3,51 |
| Slurry 2 | 3,52 | 3,51 | 3,51 |
| Tjaarda | pH before drying | ||
| Soil to water ratio in mix: | 1:1 | ||
| One slurry | 3,14 | 3,23 | 3,19 |
| Tjaarda | pH after drying | ||
| Soil to water ratio in mix: | 1:1 | ||
| Slurry 1 | 3,28 | 3,20 | 3,29 |
| Slurry 2 | 3,61 | 3,51 | 3,44 |
The message is not that the pH will go up a little bit after drying, but that again the soil is as acidic as a (sour) pineapple.
We’re not done yet, but the next post will tell more about the nitrogen
Scientassist 