Autumn Leaves vs Rock Dust: Mineral by Mineral Comparison

Today we are going to follow up on the next questions that have come out of the 2014 home garden field trials and put one of my garden claims to the test. What nutrients or elements do Rock Dust and fall leaves bring into the garden and how do they stack up against each other.

In order to do this I sent samples of rock dust and the fall leaves from trees that are common in my area into the lab for analysis. In consultation with an expert we selected a number of analysis methods to ensure we captured the most appropriate data to answer these question. Today we are going to take a look at trace elements

The core theory behind Rock Dust is that it adds trace elements to the soil. In addition to testing rock dust I thought I would also test one of my garden assumptions as promised.

One of my garden claims is that fall leaves from deciduous trees are a source of elements as well. In theory trees collect minerals from the parent minerals using their roots and deposit them in their leaves when they drop.

As such both rock dust and fall leaves both should be able to add trace elements to our gardens. This analysis allows us to compare them to see how they stack up.

I sent two of the leading brands of rock dust and an even mix of four kinds of fall leaves that are fairly common in my area, Birch, Poplar, Apple and Russian Olive.

In order to analyze the trace elemental make up Maxxam Analytics starts by dissolving the sample material in a strong acid to break it down to its elemental components and run through the analysis. This analysis gives results that represent both the available and unavailable forms of elements.

Plants need more then just the Nitrogen Phosphorus and Potassium to live. This analysis captures the essential elements, beneficial elements and most of the other elements that may not be need.

On to the trace Minerals assessment. Remember that in order for there to be a statistical relevant generally the difference must be larger than 10x the reportable detection limit.

Once we have separated the relevant results its time to see determine if there is a statistical difference between Rock Dust and Leaves

This is easily done by completing a Relative Percent Difference assessment. This is done by applying the following equation:

RPD = ( (x1 – x2) / ((x1 +x2)/2) * 100

For example lets calculate it for Aluminium:

((8000 – 210) / ((8000 + 210) /2) * 100 = 189.77

If the RPD is over 100 then the results are statistically different to a level high level of confidence. In this case the Aluminum numbers are different with a value of 189.
Essential and Beneficial Element Results

See video for table

Italics indicates Beneficial Element
Bold indicates sufficient concentration in both samples

See video for table

Of the other elements that are not essential or beneficial for plant growth rock dust only has additional Aluminum and Barium with leaves sharing a similar range on Strontium.

So what does this all mean?

Fall leaves have more essential and beneficial elements, then rock dust. In the two cases where rock dust has more, Iron and Sodium, the leaves still have what would be considered a good amount of Iron.

Rock Dust B and the fall leaves share more elements with the exception of boron missing from the rock dust and copper and nickel missing from the fall leaves.

The 1/2 of the elements that do not fall in the beneficial or essential element categories most were not represented in any sample. The remainder of the elements have little or no evidence to suggest plants or humans require them and some are intact known to be harmful.

In summary fall leaves and rock dust have a good spread of elements contained within them. That said neither has a full complement and in the rock dust samples there are elements that are not required and could be harmful. the additional elemental requirements likely come from a healthy compost made with a variety of ingredients.

When we start to look at releasing these elements into the nutrient cycle leaves do have an advantage when compared to rock dust. Minerals in rock dust can take an extremely long time decay and enter the nutrient cycle whereas leaves have already incorporated these elements into an organic structure and should be available much quicker.

The results will vary depending on the leaves you have available however these results give me evidence to support the claim that you can continue to add essential trace element into your garden using a free and usually locally abundant resource without purchasing a product. Simply add them to your garden through compost, mulch or mold and over time they will enter the nutrient cycle further enhancing the soil.

The lab results will be posted online. I would like to take the time to thank Maxxam Analytics for their help running the samples and analyzing the results.

We are going to continue the trials and add a poor soil trial bed. The analysis will continue to see if we can figure out what is going on and further test both products and our garden assumptions.

In order to continue to test our garden assumptions I have submitted samples of other free resources to see what they are made of. As the results and videos become available they will be posted in the playlist on screen now.

Full Lab Report:

Related Playlists
Testing Garden Assumptions:

Home Garden Field Trials 2014 Playlist:

About Stephen

The Alberta Urban Garden Channel hopes to promote organic gardening that is simple, sustainable and does not have to cost a lot. We do this by investigating the Science behind gardening, methods, practices and products to make sure that you will have the best chance of successfully growing your own food at home.