Since 2018 I have been asking my garden if some potential soil amendments that I produce at home can replace some of the soil amendments that I import into the garden. Worm castings, one of the potential soil amendments for replacing nitrogen, turned out to be too difficult to apply and too low potency for the small amount of it that I have available. I have also trialed two other materials, urine as a source of nitrogen and wood ashes as a source of calcium, phosphorus, and potassium.
In the last two years the garden told me that urine is as effective as cottonseed meal to provide nitrogen for some kinds of plants, such as corn and tomatoes. In other cases, such as for root crops, it may be less effective than cottonseed meal. It also told me that I can use as much as seven pounds of wood ashes in a garden bed and not raise the pH too much, but that it would be preferable to use that much on crops that will make good use of all the potassium that it brings. However, having only used that large quantity of wood ashes on one crop family, the alliums (garlic and potato onions) that did not make the best use of the excess potassium, I did not know how it might affect other crops.
The first two beds I plant each spring are the potato bed and the bed with greens and roots. I had some cottonseed meal left over from 2019. These crops seem to do better with cottonseed meal than urine. Rather than take the time to look more closely at the soil test results, I used the usual amount of cottonseed meal and just enough wood ashes to make up a magnesium deficiency, using Tennessee brown rock to provide the rest of the phosphorus the beds needed. Then I got those plants into the ground while I gave the whole issue more thought.
The garden is settling into a pattern of a few small deficits each season after 8 years of re-mineralization. Organic matter is in the range of 3 to 4%, which is about the best that I can expect for the amount of compost I add and the heat and length of the growing season. The pH is in the right range for vegetables and the TCEC shows that the light silt loam nature of the soil remains unchanged despite adding purchased humates. On the other hand, sulfur and phosphorus deficits have dropped to low levels. Part of the reason I am adding the humates is that they can adsorb and hold sulfur and phosphorus anions; it may be working. The lower the phosphorus deficit, the more likely it is that I can remedy it by adding sufficient wood ashes without needing to add such a large amount as to increase the pH above 7.0. The humates are stable so I should be able to stop adding them at some point. Magnesium is a little deficient, but I can easily add enough wood ashes to remedy it. The sulfur deficiency is easy to remedy with gypsum, the boron deficiency is easy to remedy with borax, and the zinc deficiency is too small to worry about.
Having noticed all that, I decided there were two questions for this year’s garden.
1. Do I want to use cottonseed meal or urine to add nitrogen to the garden beds this year? Cottonseed meal is easy to apply when I prepare each bed, but I have to buy it. I make my own urine, but last year’s results suggest that I don’t make enough of it to provide all the nitrogen that the spring and summer crops need. I could ask Mike to contribute, but it’s harder to control the amount I add in that case.
2. Do I want to use a rock source of phosphorus or use wood ashes to make up the phosphorus deficiency? Both are easy to apply when I prepare the bed. I have to buy the rock source. We have wood ashes from the wood stove to make use of, and this year adding a little over 2 pounds to each bed is enough to remedy the phosphorus and magnesium deficiency. Most likely I have enough wood ashes for all of the beds. I will be adding more calcium to an already existing excess if I use wood ashes, but we get rain during the growing season so it would be almost impossible to add so much as to create an undesirable layer of caliche. It’s only a 10% or so excess anyway.
Eventually I realized that I can ask the garden to answer the following questions this year.
1. In the bed in which I planted the tomatoes, peppers, and eggplants, I added the full 2 plus pounds of wood ashes to remedy the phosphorus and magnesium deficiencies. This bed produced good yields last year with urine as the nitrogen source, so I will collect urine for it this year as well. It will be easy to collect the 15 or so days’ worth of urine that it will need between now and the beginning of October. This bed will answer the question of the effect of adding both urine and wood ashes on yield, taste, and disease and insect pressure.
2. I will use the full 2 plus pounds of wood ashes and cottonseed meal on all remaining beds as long as I have enough wood ashes to do so. All of these beds will answer the question of the effect of using wood ashes along with cottonseed meal on yield, taste, and disease and insect pressure. Only on the bed with garlic and potato onions have I done that before and I used about a factor of three more wood ashes that time.
That’s all for now. See you in another month or so!
