August 10th to 16th, 2015
We received our soil testing results this week. We took separate samples from four of our raised beds, because we wanted to test to see if the beds had any variations in the nutrients available to the plants. Last year we took samples from all the beds and combined them into one sample for testing, but we worried that this process did not give us a granular enough view of what was happening in the garden. As it turned out, there are only very minor variations from bed to bed and the results were very similar to what we saw last year with the combined test.
As we had already known, our Phosphorus levels are quite high. We are not absolutely certain how the levels became so elevated, but we have a pretty good guess. Last summer, when our plants were not thriving, we purchased a great deal of turkey and cow manure compost to augment the nutrients and organic matter in our soil. We applied several inches of this compost to each of our beds.
It is important to note that compost, made up of food scraps and yard debris, is quite different from composted manure. A distinction we were not really aware of at the time. As it turns out, composted manure can have wildly varied nutrient availability depending upon the diet of the animals producing it, and cows will pass almost 85% of the phosphorus in what they eat on into the soil. It may be that the manure we received had very elevated levels of phosphorus, which we passed on into our garden at a very high application rate.
The problem with high phosphorous levels is that phosphorous can lock nutrients into inaccessible states so that they cannot be absorbed by the plants. Even though we have sufficient nutrients in the soil, as our tests show, our plants are still experiencing nutrient deficiencies due to the over action of phosphorus in our soil.
Luckily, there is a fairly simple remedy for the high phosphorous problem, and that is a foliar application of iron and zinc. We have been using Liquinox Liquid Fully Chelated Iron & Zinc since receiving the high phosphorous reading last year and are pretty happy with the results. I do notice that the plants perk up after using it and it is wonderfully easy to use. I find giving the plants a misty bath of supplements in the evening a very pleasant experience, and that is a good thing, since it looks like we will need to continue to do so for many seasons to come. High phosphorous levels can persist for as long as a decade. The lesson for us has been, the more you know about your soil and the amendments you use, the better. We thought that if composted manure is good then more of it would be even better, and that is simply not the case. (We fell for the “Excluded Middle Fallacy”.)
The pH Problem
Another issue with our soil that has been identified in this test is an elevated pH level. This means that our soil is slightly alkaline, and this can cause problems for plants as well. Interestingly, the problem this causes is very similar to the problem of too much phosphorus. Soil that is too alkaline can make it difficult for plants to absorb micro-nutrients from the soil. Now, don’t fall for the excluded middle fallacy again and think that if alkaline is bad for the plant then acid soils must be good. At elevated acid levels, the macro-nutirents in the soil become unavailable to the plants, so that can be bad too.
As one might imagine, different plants desire different pH levels for optimum health. Each plant has evolved in a different ecosystem, after all. There are many factors which can effect the pH of the soil, from the basic mineral content to microbial life. In our neck of the woods, it is no surprise that the soil reads alkaline. Our bedrock here is limestone, and if you wanted to make your soil more alkaline, lime is what you would add to do it. In areas where sulfur is abundant, I am sure you would find that the soils leaned toward the acid side, since sulfur increases acid levels in soil.
Now, even though there are a variety of different plant preferences for pH level, most of our fruits and vegetables prefer a pH level from 5.5 to 7.0 and will be able to adequately extract all nutrients at that level. This means that we need to bring our pH level down at least half a point and preferably more. This is going to be very difficult for us, since we are working against high levels of lime in the soil and in our well water, but there are a few techniques we will engage to get the job done.
- Apply Compost Tea – Compost tea will not alter the pH of the soil on its own, but rather it will increase the microbial activity of the soil which can make both micro and macro nutrients more available to the plants, which means the plants will be able to manage in a wider range of pH levels. We hope regular application of compost tea will decrease the change in pH we will need for a thriving garden.
- Lower Water pH with Vinegar– We are also going to lower the pH of the water we use to water the plants using vinegar. We mostly water with rain water collected from the roof of our garden shed. We will measure the pH of the water and add our own home grown vinegar to lower the pH into the range we desire. This technique is temporary. It will not permanently alter the pH of the soil but it will create a more acid environment during watering and assist the plants with absorption of nutrients.
- Increase Organic Matter Through Mulching – We will begin mulching with raked leaves from around the property. These raked leaves will not only keep the soil moist, they will also compost in place, increasing the organic matter in the soil and introducing bacteria and micro-organisms to encourage healthy soils. Acid in soil is a bi-product of yeast and bacterial functions and so increasing the bacterial life should have a positive effect on the pH levels of our raised beds.
- Supplement with Peat Moss – We will be investing in a bit of peat moss to complement our leaf mulch. Peat moss is highly acidic usually coming in as 4.0. This is way to acidic for most plants, so we have to be sure to be very careful with this supplement. (The Oz Garden has some good cautions) Still, we have to move that pH a whole point, and we hope this will help. I have not yet, however, found a good way to determine how much to use for the desired result, so I will keep looking for more info on this before I engage the practice.
- Supplement with Sulfur – Sulfur can be applied in two different forms, aluminum sulfate and pure sulfur. Clemson University has a nice quick write-up about this. Aluminum sulfate will have an immediate effect, but I believe that we will go with the more slow acting sulfur. Sulfur lowers the pH when acid is produced by bacteria consuming the sulfur, so the change in pH will take place over time. I think this gradual change will be better for the beds and plants in them, and I am hoping that with the other steps we are taking it will require application less often and in smaller amounts.
The last concern we have from our soil tests is low levels of nitrates or nitrogen in the soil. Interestingly, slightly alkaline soil can actual cause the loss of nitrogen as it is converted into ammonium gas and is lost to the air. The Soil & Health Association of New Zealand has a very interesting write up on nitrogen. Considering this issue, we are hopeful that improving the soil pH will also help with our nitrogen levels.
In the meantime, we will need to also add nitrogen to the soil, but we cannot do that with conventional fertilizer, that would also contain phosphorus, which we cannot add. For this reason we are turning to alternate organic sources of nitrogen. Fortunately Blood Meal has just nitrogen in it, with none of the other macro-nutrients. For now, we are purchasing blood meal, but we will be planning to use the blood from our deer next season to make our own. (directions available at Post Apocalyptic Guide)