A Soil Test For The Chicken Run
When I first decided to adopt the Strawberry Moon Chicks and began building the first coop, I intended for it to be a “chicken tractor”. That is, I intended to move the coop periodically so the chickens would have a steady supply of fresh pasture. This proved to be a more difficult a job than I anticipated. That coop has been in the same spot for three years, sitting on cinder blocks because the wheels buckled under the weight of the too-big coop. I think I have finally remedied that problem and if so, that coop is moving on Saturday. As soon as the hen coop is secure in its next location, I plan to annex the old chicken run into my garden.
Chickens have a long history as garden helpers. Their presence ads a great deal of fertility to land, and prominent growers such as Eliot Coleman include them as a successful part of organic crop rotation. However, three years is too long a rotation for optimal soil enhancement, and it occurred to me that their extended stay might have done some damage. A little googling revealed the following possibilities: the soil might be too salty, the soil might contain too much phosphorus (the ‘P’ in ‘NPK’), and the soil might be too low in organic matter. My chickens do have a large run, and I do add straw and pine chips to it sometimes, so I hoped the land would be fit to garden next summer. I ordered a soil test to find out.
A brief note about soil testing, because people ask me about this a lot. It’s common advice to “do a soil test” before starting a new garden. When people say this, they mean a standard fertility test, which might be free if your extension service offers it, or might cost about $10-$15. Either way, you find out where you can have this done by calling your county extension office.
In my case, free tests aren’t available, and so I took my soil sample to a local agricultural supply business. They called earlier this week to tell me everything is A-OK, and my garden expansion may proceed as planned. Yay! Upon my request, they also sent me the specific lab results. I went through each result individually to learn about the implications and optimal range for each test. This research process was very tedious, so I’m sharing all my notes here for your benefit. The hard work was worth doing though, because in the process, I learned that my celebration might have been premature. There are some soil imbalances, but it remains unclear whether or not they’ll have an impact on plant health next season.
These are the results I received from my standard $15 soil test.
| Test Name | My Result | Explanation |
|---|---|---|
| CEC | 13.7 | CEC stands for “Cation Exchange Capacity”. This metric indicates the capacity of the soil to absorb and retain nutrients, and is related to the components of the soil (sand, clay, loam). Our 13.7 is a fine number. This article by Spectrum Analytic provides a detailed explanation of CEC. |
| OM % | 2.7 | OM stands for Organic Matter. According to Cornel University, most agriculturally productive soils have between 3-6% Organic Matter. So it looks like we’re a little low, but not by much. |
| pH | 6.8 | pH is a measurement that almost everyone will recognize. It stands for “potential of hydrogen”, and it’s the scale we all use to measure how acidic or alkaline something is. Lemon juice is acidic, and has a pH of 2. Household bleach is alkaline with a pH of 11. Neutral pH is 7. Most common garden plants prefer soil with a pH between 6-7, so we are right on the money. |
| Lime Index | 69.15 | This measurement tells us how difficult it would be to raise the pH of our soil. Since our soil does not need to be any more alkaline, this particular measurement isn’t very useful in our case. However, you can read more about this indicator in this great article from Michigan State University |
| P(Bray) lbs/ac | 222 | This test measures the amount of phosphorus in the soil. According to Penn State, the optimal range is 30-50 lbs/acre. Our 222 is a very high phosphorus number. |
| K lbs/ac | 209 | K stands for Potassium (it’s the K in NPK). According to Purdue University, this number is in the optimal range. |
| Ca lbs/ac | 3782 | This test is for calcium. According to Ohio State University, the desirable amount of calcium in pounds per acre is 800–16,000. Our test result is within this desirable range. |
| Mg lbs/ac | 3782 | This test is for magnesium. According to the same article by Ohio State University, the desirable amount of magnesium in pounds per acre is 150–2,000. Our result is above the desirable range. |
| K sat’n % | 2.0 | This test measures potassium saturation in the soil. The desirable range is dependent upon the CEC value (ours is 13.7) so according to the above mentioned Spectrum Analytic article about CEC, our desirable range for potassium saturation would be between 3-4%. Looks like ours is a little low. |
| Ca sat’n % | 69% | This test measures calcium saturation in the soil. The ideal range is 50-70, so it looks like we passed this test! See the above mentioned Spectrum Analytic article about CEC for more info about calcium saturation. |
| Mg sat’n % | 22 | This test measures magnesium saturation. Based on our CEC, our ideal range would be 8-20. Looks like we are a little high. More info can be found in the above mentioned Spectrum Analytic article about CEC. |
| Base sat’n % | 93 | Base saturation. This appears to be the sum of the previous three numbers. |
| H sat’n % | 7.4 | Hydrogen saturation. Ideal value is less than 10%. This result looks fine. More info on Hydrogen saturation is available here |
| Ca/Mg | 3.2 | Calcium to Magnesium ratio. According to Michigan State University, values between 2-8 are fine, as long as the soil has enough calcium and enough magnesium. |
| Mg/K | 11.1 | This is the magnesium to potassium ratio. I tried, but I haven’t been able to find out the desirable range for the number. I’m told it’s not very important, anyway. |
In summary, our chicken run soil has elevated levels of phosphorus and magnesium, and low organic matter. The low organic matter may indicate that some erosion has occurred (due to the chickens scratching). This is the easiest problem to remedy, and I will do so by spreading a thick layer of mulch on top of the soil. I’ll prevent this from occurring in the future by keeping a thick layer of mulch on the new chicken run. Sodium and nitrogen tests were unfortunately not included in our basic soil test package. I spoke with the specialist at the local agricultural supply company, and he feels confident that a sodium test isn’t necessary, since our local soils all contain very low levels to start. He also said that since nitrogen leaves the soil so quickly, even if the soil has elevated nitrogen levels now, they should normalize by spring. He does not believe our elevated phosphorus and magnesium levels will cause any problems in the garden. I also discussed these results with my county extension agent. She agrees that the elevated phosphorus and magnesium aren’t likely to cause problems in the garden by themselves, but suggested that we might need to add higher than usual amounts of nitrogen, potassium, and calcium to bring the nutrients into balance with each other. She is unsure whether the garden will grow well or not, but reminded me that all gardening is really an experiment.
Inspired by my county extension agent, I think I’ll grow an experiment garden on the old chicken run. I’ll plant a wide variety of species and see which ones grow well post-chicken, and which ones struggle. I will not plant any precious seeds (ones that need to be saved and preserved for future growing seasons) or any expensive transplants in the experiment garden. As always, I’ll report my findings here. Meanwhile I hope you’re all warm, cozy, and well.
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