I had a soil test of my garden done last summer, and I’ve been meaning to post the results. Since they are in Dutch, and probably not many of my readers can understand them as they are, I will attempt to translate. However the original report can be found here.
You can compare this to my earlier do-it-yourself efforts at soil testing.
Measured values are given first, followed by target values in parenthesis if these are given in the original report.
Organic Material 10.3%
Calcium 2-5%
pH (KCl method) 7.2 (>6.4)
Available Nutrients:
Phosphorus 58 (45)
Potassium 22 (21)
Magnesium 230 (125)
Nitrogen 1.4 (1.0)
Unavailable Nutrients:
Phosphorus 1370 (1000)
Potassium 5 (7)
Biological Activity:
Detected mg of CO2 per 100g per 7 days 86 (70)
Conclusions and Advice:
Conclusion: Soil has a high organic content, and a good pH level. For most nutrients, there is sufficient to excessive available and unavailable amounts. There is sufficient nitrogen and biological activity.
Advice: Add 300 liters of fresh manure or high quality compost per 100m2. As an alternative, 50 liters of dried cow manure per 100m2. The actual amount varies with crops grown. Lime loving plants (soft fruit, potatoes, cabbage, carrots, etc) 2 kg of (dolomite) lime per 100m2. Nitrogen loving plants (soft fruit, potatoes, leaf vegetables, cabbage, beet, etc) only in case of slow growth 500g nitrogen per 100m2 in the form of dry organic fertilizer. For example, this can be 4Kg bone or blood meal per 100m2. Further fertilizing is not necessary.
The advice seems to be open to some interpretation. I probably don’t add quite as much compost as they say here, and I don’t add any of the other fertilizers or manures, but since they say amounts vary with crops grown I guess you could say I’m following the advice. It’s worth mentioning I also grow a lot of nitrogen fixing plants.
At the same time I could be adding an awful lot of manures and nitrogen fertilizers and also be following the advice. 300 liters of fresh manure per 100m2 is an awful lot!
I think it’s more a part of the culture here to depend on soluble nitrogen in the form of manures or fertilizers, rather than fixed nitrogen, and that may be part of the reason the advice is given in the way it is. The test doesn’t seem to show fixed nitrogen.
The excessive availability of some of the nutrients is probably related to past chemical fertilizer use.
I purposely waited until the end of the second growing season to do this test, so I had a chance to amend the soil and grow some nitrogen fixing plants. I also wanted to give any previously used fertilizers a chance to wash away.
I do sometimes notice low nitrogen levels, and I also notice when I grow a heavy feeder like sweet corn, the soil is pretty depleted for the next season. Mostly my experience is that my soil is in pretty good shape, and this test seems to confirm that. It can also be true that some of the excessively high levels of the major nutrients (NPK) can tie up and make unavailable some of the micronutrients, and I could be having problems with this.
Interesting Patrick
What’s your annual rainfall? What’s the underlying geology where you are? I would have thought a pH of 7.2 was at the high end for the availability of some nutrients. As usual, the plants themselves give a pretty clear indication of any underlying problems. If they look OK, then they probably are.
Hi Owen,
Our rainfall is about 800mm per year.
Yes, I guess 7.2 is a little high. I even still give the odd handful of lime to fruit trees and soft fruits. I have a meter with a probe, not very accurate, but still gives a pretty good indication of pH. With this I can see widely different readings in different places. A few meters outside my garden I have even had readings as low as 5.5. It is possible the previous gardener used excessive amounts of lime, but I would have thought it would have gone away by now.
Historically Amsterdam was a peat bog, but it’s a long way by now from it’s natural state. Still, for this reason, people often advise me to be sure to use lots of lime in my garden to counter the acidity of the peat.
Managing water levels over the years with dikes and canals has caused the ground to sink. My garden is about 1 meter below sea level, but the original ground is much lower than that, probably another 3-4 meters down. To make the land usable, they’ve filled it in with sand. One of my nearby gardeners said he dug a hole as deep as he could, and about 1.5 meters down he encountered a layer of plastic, probably put there to help keep the ground from settling.
It’s kind of interesting gardening with so much water. The water usually sits about 30-50cm below the garden, meaning plants with roots at least that deep never need any watering. The land is ‘well drained’ so to speak, and the water is always fresh and well circulated. There are of course plants that don’t like wet feet, but most plants seem to cope with it okay. Everything does flood from time to time.
Hi Patrick
Thanks for the clarification – sounds like you live in Chinampasterdam. If it worked for the Aztecs, why not the Dutch?
That’s pretty neat Owen! I had never heard of Chinampas before. I wonder if there are some parallels… At a brief glance, they have an age old system based on ancient rock formations and other things that are a far cry from my wet sand dune. When I have time, I’ll read up on it and see if I can get any ideas.
You might be interested in this article in the New Scientist about the Chinampas, that I read a while ago. Unfortunately it has been made private, but if you are quick, you might be able to get the cached version. See cached version here: http://bit.ly/avKltN
Basically, the article posits that subterranean strain of bacteria churned up by the nearby volcano, lives in the waterways and is the reason for the fertility of the Chinampas.
Scientists discovered highly heat tolerant bacteria that had excellent composting properties.
Article is fascinating.
David.
Hi David,
I’ve just had a chance to read it. The article is really interesting! I’ve noticed compost seems to go really fast in my garden. During the summer I tend not to bother making a pile per se, but rather just leave pulled weeds in place, because they decompose so quickly anyway. It makes me wonder if I have a similar bacteria.