It is time to begin getting dirty, and turning over new ground. I plowed the first Grow Appalachia gardens yesterday and have been turning over the wetter beds at PMSS with a shovel. It feels great to be out the gardens, with dirt all over my arms, and sunburn. Almost every Grow Appalachia participant has dropped by with a bag of soil for me to take to the Harlan County Extension Service for testing, and we have received quite a few of these back. I am thrilled to see that these participants are holding up their end of the bargain (I have held seeds hostage until I see soil)…
Now, I am woefully undereducated, about soil. I love touching it, smelling it, working with it, but I don’t really understand how it works. And I don’t completely understand soil tests, especially in regards to organic production systems, since organic does not just strive to replace petroleum based products with more natural external inputs, but to change the way we work within the system to build healthy soil. That said, I need to find out. This post does not claim to illuminate soil testing, but will reflect my struggle with understanding how to interpret my soil test results. I welcome any knowledge you all would like to share with me through a comment on the blog or an email to firstname.lastname@example.org
When you receive the recommendations for fertilizer application on your soil test result sheet it does not mean that by adding the amendments this growing season your soil will be fixed. UK (who conducted our Grow Appalachia program’s soil tests) states that the rates of nutrient application recommended are for when a crop is grown each year, and it assumes that it will take four years to greatly increase the amount of Potassium (K) and Phosphorus (P) present in the soil. During these years, using cover crops, green manures and compost will also help improve your soil quality (nutrient availability, organic matter content, and texture).
How to interpret the fertilizer recommendations on your soil test
The numbers on a bag of fertilizer let you know what percentage (by weight) of each nutrient is present in the bag. Technically, it represents the percentage of N, P2O2 and K2O that is available, but for our purposes, nitrogen, phosphorus and potassium will do.
For example, a 50lb bag of 10-10-10 is made up of 10% N, 10% P, 10% K and 70% filler. This means that the 50 lb bag of fertilizer contains 5lbs of N, 5lbs of P, and 5lbs of K, making your total nutrient weight 15lbs per bag. The remaining 35lbs in the bag is made up of fillers to help the nutrients spread from the bag. Without any filler we would over apply in some areas of the garden and under apply in others; the filler allows for an even application. When using synthetic fertilizers this helps to prevent us from burning our plants with too much fertilizer. This filler material is usually composed of sand and limestone. In organic fertilizer the filler material is usually made from trace minerals which help supply the nutrients that a typical N-P-K fertilizer does not.
A handy formula: % nutrient on bag * lbs in bag = lbs nutrient present in bag
Example: In a 50lb bag of 10-10-10 the lbs N present is 0.10*50 = 5lbs
In a 40lb bag of Harmony 5-4-3 the lbs N is 0.05*40 = 2lbs
|Soil Test Results for the Pine Mountain Community Garden|
Example: Making sure Maggie uses the correct amount of fertilizer (referencing the above image):
Maggie’s soil test calls for 2-3lbs N and 3-5lbs K. Her P level is Very High.
As I understand it, most soil tests do not test for N, but make recommendations for N based on what they deem necessary for plant growth during a season. It says right on the results sheet that were heavy application of manure or compost has been used not to apply N fertilizer. So Maggie may not need to apply too much N since she is using some compost (although not what I would call a heavy application so I am going to go with the recommendation)
Using Harmony 5-4-3 in a 40lb bag (which is what the Grow Appalachia program is ordering for all sites)
N = 0.05*40 = 2lbs
P= 0.04*40 = 1.6lbs
K = 0.03*40 = 1.2 lbs
So Maggie can apply one 40lb bag to her garden space (assuming it is 1000ft2). She will be short some of the needed K if she does this, but her P is Very High and she does not need more than 3lbs N applied. Maggie can probably get along without using more Harmony 5-4-3, but might try adding some greensand (7% potash) or kelp meal (5% potash) to the soil if she can get ahold of some. Maggie may also be alright with her K levels if she adds all of her compost to the garden.
Alternative to using an all purpose fertilizer: Maggie may also be able to add her compost, some wood ashes (%7 or more potash), kelp or greensand (for K), and some blood meal (15% N) instead of using the Harmony 5-4-3.
*Note on using wood ashes – Do not let them stand in the rain, as the potash would leach away. Wood ashes can be mixed with other fertilizing agents, side dressed around growing plants or used as mulch. Avoid contact between freshly spread ashes and germinating seeds or new plant roots by keeping ashes a few inches away from plants. Wood ashes are alkaline.
Notes on soil fertility
When applying soil amendments to the soil we should be looking at our garden as a whole system. We should be “feeding the soil” not just “feeding the plant”. We don’t want to just apply fertilizer in order to get a crop this year; we want to build our soil health so that we will have crops for years to come. So think about maintaining your optimal soil fertility – adding the amount of nutrients you soil test recommends in the form of slow release organic fertilizers, starting a compost pile, rotating your crops, planting cover crops, etc! Look at your soil texture, look at your plant roots in the summer to make sure they look healthy, read up on how soil works as a living thing…
|Soil testing is a good way to start on the path toward soil health, but it mostly takes the chemical aspect into account. We also need to look at the physical condition of our soil and the biological properties (earthworms, microbes, fungi, etc.)|
CEC: Cation Exchange Capacity. What does this mean?
If you would like to learn about the Cation Exchange Capacity of your soil, shown on you soil test as CEC, or what the Buffer pH means please read this article. It explains in simple terms what these terms mean and what they mean for you as a gardener.
Explains how to take a soil sample: http://ces.ca.uky.edu/livingston-wp-content/uploads/agr16.pdf
2012-2013 Soil Nutrient recommendations and some insight on how to read a soil test:
Intepreting WV Soil tests. This document has some useful information for other state tests as well. http://anr.ext.wvu.edu/forage/soil_test_report