One of the claims Steve Solomon made in his book The Intelligent Gardener is that after several years of re-mineralizing garden soil in the way that he describes, the phosphorus content of the soil tends to come up to the appropriate level for that soil and remain that way for several more years, even without adding any more phosphorus-containing amendments to the soil (see pp. 139-144). Since phosphorus was deficient in my garden for the first few years that I practiced Solomon’s method of soil re-mineralization, I had to add a few pounds of phosphate rock to each bed in my garden each year. None of the organic sources of phosphorus contain more than 10% phosphorus by weight, and phosphate rock sources are finite and heavily exploited already. If re-mineralization can substantially reduce the need to add sources of phosphate over time, this would be good for gardens, the gardener’s wallet, and the earth. Now that I’ve been re-mineralizing my soil for almost a decade, let’s see if Solomon’s claim applies to my garden’s soil.
Below you’ll find a spreadsheet with the results from Logan Lab’s soil testing for total cation exchange capacity (TCEC), pH, and percent organic matter and the calculated deficiency or excess of several minerals from fall 2014 through spring 2023. For calculating the excess or deficiency of each mineral I used the 2014 revision of Solomon’s acid soil worksheet and the reported values for each mineral from Logan Lab’s soil test.
Notice that starting with spring 2019, the deficiency of phosphorus has decreased to a small fraction of that reported through fall of 2017. In fact, phosphorus was in excess in spring 2019, and the past year’s deficiency was only about 10% of the deficiency prior to 2019. I can remedy this slight deficiency with more readily available soil amendments, such as the wood ashes from burning wood in our wood stove. Wood ashes also supply a goodly amount of calcium and some potassium, two other minerals that can be deficient in my soil but less so since 2019.
Given that I have a light silt loam soil (low clay content, as shown by the TCEC being less than 10) and a hot, long summer that reduces the organic matter percentage that my soil can attain, I think that my garden soil is now almost as good as it can get. It would be ideal to add some more compost to it than the minimum that I have been adding, which would help to keep all the minerals available during the full growing season. Next year I’ll try adding four 5 gallon buckets of compost to each 100 square foot bed instead of the three buckets I have been adding. With the smaller number of beds I’m now planting, I should have enough compost to go around. I will continue getting the soil tested each spring and re-mineralizing as needed to address whatever small deficiencies remain in the soil. I’ll add either cottonseed meal or urine for nitrogen; last year I added cottonseed meal and I expect I’ll do so again in 2024 because it’s easier to handle than urine is. However, if cottonseed meal ever becomes difficult to obtain, I’ll collect and apply my urine for nitrogen as I have done in some past years.
The take-home message is that Solomon’s method has done what he said it would do: it has created a balanced garden soil that grows delicious vegetables in a small space. Those of you who are interested in improving your garden soil and are willing to deal with some chemistry and math would do well to read his book, and try his method if it appeals to you.
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