Tuesday, June 5, 2012

Soil Testing: results and interpretation

The image below shows the results of my spring 2012 soil test for my lawn areas. This was the $33 test from University of Maine Cooperative Extension. While the test may seem a bit expensive, the information provided is well worth the price.



2012 Soil Test Results



Previous years' tests had suggested I needed to add more compost (hence my earlier blog showing overspreading compost), and this test shows that I can still use a bit more compost. 


My calcium and pH levels are shown as above optimal, but the levels shown better suit my grass strain (see photo below). I achieved these higher levels through the addition of gypsum (gypsum raises pH, makes soil nitrogen more available, and prevents compaction and salt damage) over a four-year period (I used approximately 80 pounds per year on my lawn area). I will have a blog later this month devoted entirely to gypsum.


Photo of lawn-- look at that beautiful clover!




Interpretation of Soil Test Results


Macronutrients (N-P-K)
 These are all in the reasonable range. Some may say that my nitrogen level is low. I would not argue that the reading is low, but I expected as much. This is before any work on my lawn and my addition of compost and vermicompost tea will get the microorganisms fired up to start making nitrogen available. Also, I have clover in my lawn to pull nitrogen out of the air and fix it in the soil. I will not “fertilize” my lawn with nitrogen based fertilizer because it is not really needed. If you read the fine print, I would use 2 pounds of nitrogen per 1000 square feet, but only ½ that in late August (because I mulch my clippings) and because of organic program I would use only ½ of that. That takes me to ¼ pound of nitrogen per 1000 square feet. My compost overspreading this spring should supply my needed nitrogen as well as any sulfur and potash.


Soil Life (Microorganisms)
My microbial biomass index is 44ppm, which is on a 1-100 scale. I am trying to get closer to 60ppm (optimal range). As I add more compost to the lawn (recall that I took these samples before my spring 2012 compost overspreading) the level will increase.


Micronutrients
The decrease in micronutrient availability to plants as pH increases is not a great concern to me because it is a balancing act (given my increased pH and additions of humus-rich compost to the yard). Also, I plan to supplement my vermicompost tea with sea weed this year to boost the level of micronutrients that are available to the grass plants.


Long View
My long-term goal is to have no external inputs to my lawn (just aeration, overseeding as needed, and vermicompost tea), so everything I do is a step in that direction. It is important to remember that small steps are the best approach. Make sure your additions are based on the recommendations in the soil test. You don’t want to overshoot—that would waste both money and time. Remember that I am mulching my lawn clippings, so there is no net loss of anything (macro or micronutrients).


Early in your organic switch, you should test your soil annually to check your additions. After that you can back off to once every three to five years-- preventive lawn maintenance. If lawn problems develop more frequent testing may be necessary. 

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