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How to fill out Solomon's soil analysis worksheets

Soil analysis spreadsheetBefore I dive any deeper into soil science, I thought I'd walk you through filling out Solomon's soil analysis worksheets (which you can download for free here).  You'll notice there are actually six pages of worksheets in that file, which consist of two pages each for acidic soils (pH less than 7), "excess cations" soil (pH 7 to 7.6), and calcareous soil (pH greater than 7.6).   I actually find it much easier to make a spreadsheet page for each soil sample since the program can do the math for me, but I'll fill out a worksheet below to help you get an idea of the process.

Pasture soil analysis

Since I sprang for a test from Logan Labs, as Solomon recommended, it's pretty simple to fill out the column of actual amounts.  The only tricky parts are:

  • You need to convert from ppm (parts per million) to lb/acre (pounds per acre) for certain readings.  Solomon explains that you simply multiply ppm by 2 to get lb/acre, which I'm a little dubious about.  His reasoning is that we sampled our soil to a six inch depth, and soil scientists estimate that amount of earth weighs about two million pounds per acre.  When I start cancelling units in the conversion, though, I feel like there should be something factored in to take the atomic weight of each mineral into account, but I stuck to Solomon's math.  (Roland, help?)
  • Logan labs reports phosphorus pentoxide instead of elemental phosphorus, so you need to multiply their result by 0.44 to get lb/acre for phosphorus.

The target column is a little more complex, but is mostly basic multiplication.  The one portion that might cause a hiccup is potassium (K) --- you get that amount from the chart at the bottom-left of the worksheet based on the TCEC of your sample.  Similarly, boron, iron, and manganese targets are based on TCEC, as is explained in the "calculating target level" column.

Chicken pastureFinally, you subtract the actual amount of each element (in lb/acre) from the target amount to figure out how much excess or deficient you are.  Since Solomon labelled the last column "deficit", I put excesses in parentheses.

The sample I used is a pasture that has been grazed with chickens for a couple of years with no other amendments, so I figure it's probably similar to the soil you might find in a new garden spot.  You'll notice the soil is acidic and a bit low on organic matter, without as much capacity for cations as you'd like, and it has too much of a few nutrients but too little of some others.  Tomorrow, I'll move on to the back side of this worksheet to show you how to deal with those excesses and deficits.

Our chicken waterer never spills on pastures, so it's perfect for permaculture chickens.



This post is part of our The Intelligent Gardener lunchtime series.  Read all of the entries:




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When we are talking about ppm, we first need to know what exactly it means in this context, since it is a fraction of two measurements that have the same unit and is therefore dimensionless. E.g. ppm can be an elongation (in/in), solution by weight (lb/lb) or fraction by particles (e.g. mole/mole).

Assuming that the report is in lb/lb and not in mole/mole, we need to figure out the dry bulk density of soil. We use the dry density because we are interested in the mass ratios of the solids in the soil. The particle density of minerals varies a bit, but not much. The dry bulk density of soil can vary a lot depending on the exact mineral composition, the amount of organics and the degree of compaction. It is generally reckoned to be between 1.0--1.6 kg/dm³.

Six inches is 1.524 dm. One acre is 404685.64 dm². So this soil would have a volume of 616741 dm³. With the given dry bulk density range, you would have a dry soil weight of 616741--986786 kg, or 1359681 to 2175490 lb. So under the abovementioned assumptions, 1 ppm would correspond to between 1.36 and 2.18 lb/acre.

Comment by Roland_Smith Thu Jan 17 14:30:59 2013

Hi Anna,

One consultant suggests 3 ppm of Mo so the soil microbes work well.

And humans do better with some V, Se, Ag, Cr.

Once you have added greensand and seaweed to somewhere and it has settled in a more detailed soil report would probably be well worth it :).

I gather you have no problem with having enough water :) :).

John

Comment by john Fri Jan 18 10:58:07 2013