Tips for Soil Testing: A Gardening Necessity

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If you want a vegetable garden this fall, get your garden soil tested soon. Tests are free from University of Agriculture Division of Agriculture through your county extension agent. A test will tell you this about your garden’s soil:

  • Levels of 10 soil nutrients critical for health and vigor, as well as flowering and fruit.
  • Its pH, which affects growth and how well plants can absorb nutrients from the soil.
  • Recommendations for three major nutrients (nitrogen, phosphate, and potassium), if your soil needs them. (A standard recommendation for nitrogen is given rather than specific to your test results. It is too unstable to test for reliably, an agent told me. The other two are based on your test results.)
  • What to add to correct a pH if it is too acid or too base (neither is good). Plots that have never been gardened can be extremely acidic, far below range for vegetables to thrive.

The report recommendations for home gardeners will be per 1,000 square feet and will be phrased something like: “Apply 2 lbs. of urea or 3.5 lbs. 34-0- 0.” You may be stumped by such a statement. You don’t know if urea is something you’d want to use on your garden, even if you knew a source. You may want to use something else but don’t know what or how much you’d need.

The 34-0- 0 tells you the percentages by weight of nitrogen (N), phosphate (P), and potassium (K) in urea. Urea is 34 percent N.

If this is already sounding too complicated, DO get the test done and then DO this, ideally a month or so before you plant: Sprinkle as evenly as possible over your garden, and work in well all at once, the following:

  • Lime at amount recommended. Be sure to get agricultural lime, NOT gypsum or dolomite, unless the report says to.
  • A layer of well-decayed compost, two inches or more. Do not rely only on compost to supply needed nutrients. Its main value is added organic matter, which improves availability of other nutrients.
  • A good all-purpose organic fertilizer, one that covers the spectrum of essential nutrients. Apply at a higher or lower rate, depending on what you know about your soil needs.
  • Optional: Trace minerals. Two sources: Azomite volcanic rock dust or kelp meal.

You may want to be able to select specific fertilizers (e.g., blood meal or kelp) to remedy a specific deficiency. To calculate how much you’ll need, use your report recommendations. In the example above, the report said the amount of pure N needed was: .68 lbs. (34% of 2 lbs.)

If you know the rates of N in other products, you can do the math or a make rough estimate:

Blood meal (12% N) has about one-third the N that is in urea (34%) so you would need almost three times as much (6 lbs.). Or you can solve for x: .68 divided by .12 = 5.66 lbs.

Feather meal (16% N) has about half the N that is in urea so you would need nearly twice as much (4 lbs.). (.68 divided by.16 = 4.25 lbs.)

Alfalfa meal (3% N) has about one-tenth the N as in urea so you would need a little more than 10 times as much. (.68 divided by.03 = 22.7 lbs.)

If any of what I just said makes sense, you are now off to the races!

Locally I look to Farmers Association for OMRI-approved amendments such as soft rock phosphate, kelp, potassium sulfate, greensand, and the three meals list above. Nitron Industries in Fayetteville stocks a wide array of such products that make the day’s drive worthwhile. And then there is always Amazon.

-Written by ALFN Vendor Nancy Dockter of Great Day Natural Produce

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