What the soil told me in 2013, and my response

In my continuing effort to become a better gardener, I’m conducting a scientific dialogue with my garden, as I described in this post from last year. I want you all to be clear about what it means to conduct a scientific dialogue. It doesn’t mean imposing my will on nature, trying to control it. As if I could! Nature is far more powerful than I am and than humanity as a whole is. At the same time, the process that became known as the scientific method contains within it a way to work with Nature as an equal partner in the dance of life. When we use the scientific method in that way I refer to it as a dialogue with Nature.

Of course Nature doesn’t speak English or any other human language. When we conduct a dialogue with her, we must ask her questions in a form she can answer. Then she answers in her own way, and we must translate her answers into our own language in order for us to understand and best respond to her lead in the dance. Fortunately, some people through the years have learned her language and written books to help the rest of us translate her language into answers to the questions that we asked, as well as answers to the questions we didn’t know we were asking and other information she chooses to give us. We can put this work to appropriate and respectful use in our dialogues with Nature.

In this post, I reported on what I learned from my garden as a result of the 2013 dialogue. One of the questions I’d asked the garden to answer was if soil re-mineralization would indeed reduce soil mineral excesses and deficiencies. In order to understand the answer she gave me in the form of the December 2013 soil test results, I had to re-read Chapters 5, 6, 7, and 9 of Steve Solomon’s book The Intelligent Gardener: Growing Nutrient-Dense Food. Solomon has learned how to translate soil test data from Nature’s language into English and he very generously and capably shares this knowledge with us. With that background, I think I understand what my garden soil is telling me and how to respond in 2014. I will share that with you here. Perhaps it will inspire some of you to conduct a dialogue with your soil and in the process learn some of Nature’s steps in the dance of life.

First, let’s look at differences in TCEC (a measure of the soil’s ability to hold on to various elements found in positively-charged forms), pH (a measure of whether the soil tends acid or alkaline) and organic matter percent between the April 2013 test, before re-mineralization, and the December 2013 test after re-mineralization and at the end of the growing season. They are shown below.

                        TCEC      pH         Organic matter, %
Apr. 2013        6.91        6.40        3.99
Dec. 2013        7.54        6.70        4.04

Solomon explains that the larger the TCEC, the more of certain vital elements needed by the soil microlife and by plants to build and maintain themselves can be held in reserve, ready for plants to draw on when needed. (For more detail, you’ll need to read Solomon’s book -- which I hope everyone who wants to grow a better garden will do.) It appears that the TCEC is slightly higher at the end of the year versus in early spring. While that is encouraging, because I also tested lawn soil near the vegetable garden at both times, I noticed that the TCEC of the lawn soil also increased, and by about the same amount. While I applied compost to the garden (one of the things that increases the TCEC), I did not apply it to the lawn. Thus the TCEC must have risen due to something that happened equally to both lawn and garden. I suspect the slight rise in TCEC was a result of the cooler, wetter conditions during the 2013 growing season compared to the 2012 growing season. Organic matter, which accounts for some of the TCEC, burns up less in a cooler, wetter season than it does in a hotter, dryer season. This points up the importance of a control -- in this case, lawn soil -- in understanding the subtlety of Nature’s dance moves.

The pH is still in a good range for vegetables, though it should not rise any farther. I need to keep that in mind when I develop the soil prescription for 2014. The organic matter percentage is the same within error (the error level in soil testing is about 10%, says Solomon) and not too far from the maximum of about 4.5% that Solomon suggests, in Chapter 9, is possible for the St. Louis region.

The major lesson from this part of the soil test report is that if the TCEC and organic matter level can be brought up a little, allowing more of the minerals I add to attach to organic matter and clay in the soil and thus remain available to plants throughout the growing season, the crops I grow might be more nutritious and delicious than they are now. How to do that is the question.

Now let’s examine how much of each of the elements known to be important for plant growth is found in the soil before and after re-mineralization, to learn how Nature answered that question. We’ll look at the four major positively charged elements -- calcium (Ca to chemists), magnesium (Mg), potassium (K), and sodium (Na) -- first. The question at hand is whether there is an excess, deficiency, or neither of each in the soil and how re-mineralization affected that. Thus for each test date I report the difference between the level of that element as found by the soil test and the target amount for that element as calculated using the Acid Soil Worksheet in Solomon’s book. A minus in front of the number reported means a deficiency; a plus means an excess. Units are pounds per acre which is approximately equivalent to grams per 100 square feet.

                          Ca         Mg         K          Na
Apr. 2013        -198        +86        +47       -14
Dec. 2013        +55        +83        -80        -24

Before re-mineralization the garden soil showed a deficiency in calcium, which is now remedied within the 10% error level. The previous excess in potassium is now a deficiency. Magnesium is still in excess, while sodium is more deficient than it was in spring.

These results suggest that the first priority, getting the calcium level up to the recommended amount for good growth and nutrition, was accomplished. I had hoped that this would reduce the excess magnesium, which is not reflected in the test results. However, I did notice that the soil itself seems to be less sticky than it did last year, the effect I’d hoped would happen with more calcium and less magnesium in the soil.

Two important elements that are found in negatively charged forms in the soil, sulfur (S) and phosphorus (P), were deficient in both the April and and December 2013 reports, in about the same amount. It is the humus in the soil which holds onto these elements and from which plants draw them as needed, not clay and humus both as is the case with the positively charged elements. Note that the soil organic matter level, a rough proxy for humus (humus is the end stage of organic matter decomposition) did not change from April to December. This suggests that in order to get the levels of sulfur and phosphorus high enough to remedy the deficiencies over time, I should strive to increase the level of humus in my soil to the extent possible.

As for the remainder of the elements on the soil test report, all of which occur in a positively charged form in the soil, manganese (Mn) and iron (Fe) remain in excess. The previous deficiency in zinc (Zn) is now an excess. Copper (Cu) and boron (B) remain deficient.

With these results in hand I pondered what the soil was suggesting should be my next move in the dance: developing a soil prescription for 2014 that would reduce the magnesium excess and increase the levels of potassium, sodium, boron, copper, phosphorus, and sulfur without throwing the pH out of balance. Using Solomon’s Chapter 7 and the Acid Soil Worksheet as my guides, I started with the easiest elements to bring to balance: K, Na, B, and Cu. The amount of each material given is to be added to a single 100 square foot bed. For those of us used to English units, there are 453 grams in one pound.

K: 191 grams (6.7 oz) potassium sulfate
Na: 69 grams (2.5 oz) sea salt
B: 11 grams (2 tsp) borax
Cu: 21.2 grams (1 Tbsp plus 1 tsp) copper sulfate

Calphos (soft rock phosphate) will be used to remedy the phosphorus deficiency. Adding enough to erase the deficiency also adds a little calcium, but that does not concern me. Within the 10% error level that much added calcium will not throw the soil into enough excess to exceed the measurement error.

Remedying the sulfur deficiency required more thought. The potassium sulfate and copper sulfate both bring in some sulfur, but not enough to remedy all of the deficiency. At first I planned to remedy the remainder of the deficiency with agricultural sulfur. Doing that would not introduce more calcium, as opposed to using gypsum (calcium sulfate) to remedy the deficiency. But then I re-read pages 165 and 166, where Solomon discusses how to remedy excesses of magnesium, potassium, or sodium. He says to first add enough agricultural (not dolomitic) lime to resolve any existing calcium deficiency, then add gypsum in sufficient quantity to remedy the entire sulfur deficit, even though it appears that calcium will then be in excess. He says gypsum will neither increase pH (which I don’t want to do), nor does it always increase calcium to sufficiency, but it will reduce excesses of Mg, K, and Na. Last year, in contrast, I chose to add only enough agricultural lime to meet the reduced calcium need after the calcium from the gypsum was taken into account. That may be why only the excess in K was reduced by December, not the excess in Mg, and why the deficiency of Na increased. Gypsum will knock off these elements in the order of Na first, then K, then Mg. I think that because I did not add as much agricultural lime as I could have last year, the calcium level was not sufficient to knock Mg off its attachment sites.

This year, since no calcium deficiency exists, I’ll add enough gypsum to erase the sulfur deficiency. With calcium in (apparent) excess already from the addition of Calphos, I’ll not add agricultural lime this year. I hypothesize that the end-of-2014 soil test will show a reduction in the magnesium excess and a further improvement in soil texture. Thus, to remedy S and P, for the same square footage as before, I’ll also include these in the 2014 soil prescription:

S: 276 grams (9.7 oz) gypsum
P: 773 grams (1 lb 11 oz) Calphos

To best use S and P I need to increase the humus in the garden soil. Well-made compost would be the cheapest and most local source of humus. However, having read Chapter 9, I may as well admit that my compost is not the best it can be. So I considered how I might be able to add more humus. When I read the 2014 Fedco catalog and saw that their Organic Garden Supply division offered Menefee humates, I decided to try that as a possible way to increase humus content. The catalog suggests using 6 to 10 pounds per 1000 square feet in several applications and to incorporate it into the soil surface. Since this material is new to me I will add only a half pound to each 100 square foot bed this year. I hypothesize that it will increase the organic matter level slightly, but more importantly, it will reduce the deficiencies in S and P at least slightly in the end-of-2014 soil test.

It remains to add some nitrogen, in the form of seedmeal, and trace elements while I can still easily obtain these. Solomon suggests a gradual reduction in the amount of seedmeal added each year, as the soil comes into better balance and is better able to supply all the nitrogen the plants need. Last year I added three quarts of cottonseed meal to each 100 square foot bed. This year I’ll add two quarts and observe how the plants respond. For the trace elements, I’ll again add one quart of kelpmeal to each 100 square foot bed. I’ll also add three 5 gallon buckets of my compost to each 100 square foot bed, the current recommendation of Ecology Action and about the same amount as Solomon suggests adding. Since organic matter level did not change in 2013, it appears this is enough compost to maintain the organic matter level. Compost itself is a minor source of minerals from decomposed plants and the soil that came into the pile along with them.

As part of my effort to reduce weeding work and maintain a plant cover on each bed throughout the year, and because all of these materials work best within the top six inches of soil, I’ll broadcast them on the soil surface in 2014 rather than dig them in with a broadfork as I did last year. For each bed, then, I’ll first measure out the cottonseed meal, then add the humates, kelpmeal, and all the fertilizers except for the borax, mixing them thoroughly. For those beds that already have crimson clover (my cover crop of choice) or onions and garlic growing in them, I’ll first sprinkle on the soil prescription mix, then the compost. For beds that are mostly weed-free but don’t have any desired plants growing on them, I’ll put down crimson clover seed between the mix and the compost. For those beds that need major weeding, I’ll weed them first, then proceed as for a weed-free bed. If  I treat all the beds as soon as the soil thaws in March, the soil prescription and compost should work their way into the top six inches of the soil with time and as I make furrows for seeds and dig in and harvest plants. The crimson clover will, I hope, reduce the growth of weed seeds by covering the soil before, between, and after the desired crops in each bed. It will also reduce erosion by wind and water action.

Oh, and the borax? For that, I will dissolve borax in a quart of hot water first, then dilute that quart with enough water to fill a two gallon sprinkling can. I’ll water that into the bed after everything else has been added, and then water with another can or two of plain water. With so little needed and with its dissolving so well in water, this is the easiest way to add borax with no risk of overdose. Following it with plain water will encourage it to sink into the soil and wash it and the rest of the added materials off the clover and onion leaves.

So much for the soil. How about the rest of the garden? Well, that’s the subject of the next post!