One of my goals when I started this channel
was to show how we give our plants all the nutrients they need
using only compost, worm castings, and mulch from free, local, and abundant resources.
In the past, I’ve relied on garden results to prove my point,
but today I’ll put this claim to the test
with a soil test
Here in the US, soil testing services are provided at a reasonable price
by college or university affiliated agricultural extensions.
In Illinois, the University of Illinois Extension provides a list of labs
that provide testing services.
I decided to go with A&L Great Lakes Laboratories
because of their clear instructions and easy to read reports.
I chose their $30 complete test,
rather than the $20 basic,
because it tests for a wider variety of essential plant nutrients.
I decided to test the soil in the spring -
a time when many nutrients are likely to be at their lowest levels.
I haven’t applied compost and worm castings in nearly a year,
and last year’s crops certainly took up nutrients that have not been returned to the soil.
Following instructions from A&L, I took four separate samples of garden soil,
digging down to a depth of about 8 inches.
I combined the samples in a bucket, mixed them together thoroughly,
placed one cup in a plastic bag, and sent it off to A&L.
To my pleasant surprise, the results were ready in only 1 week.
Though I had hoped for a dramatic letter opening to reveal the results,
consistent with the times, they came in an email.
First, I’ll share the results line by line.
Then I’ll discuss how I plan to respond to them going forward.
Let’s start with organic matter, which improves soil tilth,
adds nutrients, and helps soil hold nutrients and water.
Not surprisingly,
after years of applying compost, worm castings, and mulch,
the amount of organic matter in the soil is very high at 20.5%.
Next, let’s look at the essential plant nutrients in the report.
We’ll start with phosphorus and potassium,
which are often added by gardeners via NPK fertilizers and other amendments.
Phosphorus plays a number of key roles in plant health,
including photosynthesis, the development of healthy roots,
and flower, fruit, and seed production.
The phosphorus level or our soil is very high.
Potassium, which plays a key role in almost all plant processes that support plant growth and reproduction,
is also very high.
So, clearly, compost, worm castings, and mulch from free local resources
added more than enough phosphorous and potassium.
and additional fertilization was completely unnecessary.
Now let's look at the rest of the essential plant nutrients in the report.
Magnesium is high.
Calcium is medium.
Sulfur is medium.
Zinc is very high.
Iron is high.
Manganese is medium.
Copper is high, and
Boron is very high.
So, at a time of year when nutrients are likely to be at their lowest levels,
there are no deficiencies of any of the essential nutrients listed in the report.
Of the 10 tested,
3 are at a medium level,
3 are high,
and 4 are very high.
Now let’s look at sodium,
the only non-essential element in the report.
The sodium level in our soil is very low.
Fortunately, this is a good thing,
because high levels are very detrimental to soil and crops.
Similarly, soluble salts are very low.
High soluble salt levels are often associated with the use of synthetic fertilizers
and are detrimental to soil and crops,
so it’s good to have a very low level.
I was very pleased with the results for cation exchange capacity,
which reflects the ability of the soil to hold nutrients.
The cation exchange capacity of our soil is high,
which means there’s a high capacity for negatively charged clay and organic particles in the soil
to attract and hold positive soil cations
such as calcium, magnesium, potassium, and ammonium.
I have to admit. I was a little surprised by the next result, but I really shouldn’t have been.
Soil in the Chicago area is often alkaline
because the area sits on top of a bed of limestone.
So, I shouldn’t have been too surprised that our garden soil is also slightly alkaline,
with a pH of 7.3.
This result confirms a point I’ve made a number of times -
namely that used coffee grounds will not acidify the soil.
We’ve added thousands of pounds of used grounds to our compost over the years and
the soil pH remains alkaline.
Large quantities of wood chips and autumn leaves have also not acidified the soil.
Before going further, I should probably also talk about nitrogen.
Though most inexpensive soil tests, like this one,
don’t test for nitrogen,
A&L did recommend fertilizing with nitrogen.
Nitrogen moves through the soil more quickly than phosphorus and potassium,
so it’s more likely to become deficient
when we reduce our compost applications.
To compensate for this, we’ll grow more nitrogen fixing cover crops
and we’ll let our plants tell us if they need more nitrogen.
Though it’s possible we may have to resort to a nitrogen fertilizer at some point,
I’d bet money that the cover crops will be sufficient
and no fertilization willbe required.
I’m very pleased with much of what I saw in the soil test results.
First of all, it’s clear that compost, worm castings, and mulch from free, local resources
have provided more than enough nutrients for our plants to thrive.
In fact, A&L Great Lakes Laboratories doesn’t recommend adding any fertilizer
to increase any of the nutrients that were analyzed in the test.
However,I am concerned that some of the nutrient levels are too high.
High phosphorus, in particular, can contribute to water pollution, inhibit mycorrhizae,
and create nutrient imbalances that interfere with absorption of other nutrients.
I’d also like to bring the soil pH down to within the optimal range for vegetables,
which is between 6.5 and 7.
I hope to gradually reduce the nutrient surpluses
by making significantly less compost.
We’ll continue to feed kitchen scraps to our composting worms
and compost the rest of our household organic waste,
but we’ll no longer compost additional free resources like used coffee grounds and autumn leaves from the community.
This will reduce the amount of compost we produce significantly
and hopefully bring down nutrient surpluses.
Though I still strongly recommend composting
free local external resources to bring nutrient levels up to optimal levels,
our soil has reached the point where, at least for now, this is no longer necessary.
Next spring, we’ll test the soil again to see if we’ve brought the surpluses down.
We’ll also check to see if nutrients that are currently not in high surplus remain at sufficient levels.
If they dip to lower levels, we’ll address them individually.
I also hope to gradually bring soil pH down to optimal levels by applying sulfur.
Vegetables absorb nutrients more readily,
and are generally more healthy, when soil pH is between 6.5 and 7.
Again, a soil test next spring will tell us how effective the sulfur applications were
and let us know if adjustments are needed in the future.
Well that's all for now.
Thank you very much for watching,
and until next time remember
you can change the world one yard at a time.