Healthy Soil Fertility

Sep. 30, 2010

Healthy soil fertility is important for healthy fertile plants. If you’re unsure about your soils ph and essential nutrients, it might be time to check with a soil test kit.

Marie Ianotti’s post on inspired the following tests. I agree with Marie that fall is the time to test your soils ph and nutrient fertility then add the correct amendments to your garden soil before spring.

I’ve also read that just adding compost neutralizes soil ph and provides all the macronutrients soil requires – no need to test.

So I wanted to know the truth, just how fertile is compost? Could soil, rich in organic matter, still be missing something?

soil samplesPromptly running out to grab soil samples and my soil test kit, here’s what I found out.

I did two tests. 1- Straight compost and 2- plain compacted topsoil with no amendments, testing each for soil Ph, Nitrogen, Phosphorus and Potassium.

(If you’re not about to run out and buy a soil test kit to check your garden soil, I posted about three free and easy tests to find out what soil is made of

, with ingredients you already have at home.)

Checking for Healthy Soil Fertility with a Soil Test kit

First, the compost. Ph was good and neutral. High in Phosphorus, decent Potassium… but I was kind of surprised when the compost wasn’t all there for nitrogen. Especially since it was made primarily of grass clippings.

soil test kit results - compost

Next, the topsoil. Ph is still neutral, but lacking in Nitrogen and Phospherous. Amending this soil would be helpful not only for healthy soil fertility but also ’tilth’ or texture, adding  pore space to allow air and water to reach the plants roots.

soil test kit results - compost

Compost will improve this soil, but we’re still lacking nitrogen. Researching organic sources of nitrogen, I found a few other people with the same test results and some interesting information about a soil test kits ability to pinpoint accurate levels of nitrogen.

It seems that nitrogen is a highly ‘mobile’ nutrient. The availability of nitrogen varies with temperature, moisture and activity of the organisms living in it. Many labs don’t even test for nitrogen due to inaccurate results.

Good to know. But should the soil be amended?

Yes, IF there’s a deficiency. A sign of nitrogen deficiency would be chlorosis found on older, mature leaves. As the plant sends available nitrogen to feed new growth, older leaves lose their color, becoming uniformly pale,  then yellow and eventually white in extreme cases.

But what if there is no sign of deficiency? Would plants grow faster, more healthy with added nitrogen? or would additional nitrogen burn plants, cause weak growth and susceptibility to disease and pest infestation. Another test will tell…

There are some readily available, organic sources of nitrogen to test if your plants would grow better with a nitrogen boost.

  • blood meal
  • fish emulsion (dry and liquid)
  • alfalfa meal
  • used coffee grounds
  • grass clippings

Blood meal and fish emulsion can be found in many garden centers, and its worth testing…

But for my next test, I will be comparing the effects of alfalfa meal, used coffee grounds and grass clippings, because they’re cheap/free and easy to find.

A 25 lb bag of rabbit food pellets costs $7 at Walmart and goes a long way. I’ve been using it in my compost pile. Its main ingredient is alfalfa meal. Ground and sprinkle lightly on top of the soil to test its effects on plant growth. If you have a bunny problem, this may not be the best to test in the garden.

Used coffee grounds can be collected in mass from any Starbucks, where they give it away for free. Used as a mulch, it can help with water retention as well as adding nitrogen.

And finally, grass clippings, which is most readily available. Gardeners have been using grass clippings as a mulch for years with excellent results. But grass gets hot when piled, so we’ll see what happens.

I did a side by side comparison of those 3 nitrogen sources on my red twig dogwood babies.  Honestly, I dont expect to see results this late in the season, but ya never know.

amendments for garden soil - nitrogen mulches

One last note, planting a fall cover crop of legumes in bare areas where plants are done growing can greatly increase nitrogen levels, breaks up compact soil and guards against soil erosion. In the spring, till the remains right into the soil.  I planted soybeans purchased from the grocery store.


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4 Responses to “Healthy Soil Fertility”

  1. Justin says:

    Very good article for the beginner. Nitrogen (Nitrate) is a highly mobile nutrient due to it being negatively charged which is the same charge as the soil. Other elements such as Calcium, Magnesium are positively charged and tend to stay in the topsoil. I would recommend using a lab as a baseline to start with.

    • Trisha says:

      Thanks Justin. I did read that nitrogen was mobile, but it hadn’t been explained why. That’s way expert 😀 I checked out your site, had no idea all the things you can test! You have great services too!

  2. Paulo says:

    Yes, this is kind of correct.

    I have seen small differences in P and K in different soil samples, but the nitrogen levels are always low. Even when I pee into it!

    If I test commercial potting soil it gives high N, but that is probably due to some readily available nitrogen ion, that the kit detects, but it doesn’t detect the normal soil nitrates. Even if plants show good lush growth.

  3. […] While you can pay a hefty fee to have a professional test your soil, you can also purchase a kit for testing your soil on your own. If you choose to go about it on your own, here are some helpful tips for testing the soil in your garden like a pro: […]

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