Part 1 – Understanding the Results of Your Professional Soil Test

soil test results for garden

Know Your Soil

It's really important to know what your soil needs before you start a fertilizing program. If you don't know the nutrient levels in your soil before dumping on a bunch of amendments, you may be wasting money on fertilizers. The most thorough test is the professional Complete Soil Analysis. That will be the test we focus on in the video and this blog.

So get out your soil results and your booklet (Understanding your Soil Analysis Report) and follow along to learn how to understand your soil analysis.

Part 1 – Chart of Nutrient Levels

At first glance your soil analysis results can look like a bunch of overwhelming numbers and ratios on a graph but these numbers all relate to each other and should be considered a whole when determining your soil’s needs. The first part to consider is the chart of nutrient levels.

On part 1 of chart you'll see the following:

  1. Percent organic matter
  2. Macro-nutrients–nitrogen, phosphorus, potassium, calcium, magnesium and sulfur
  3. Trace minerals (if you opted for the Complete Soil Analysis-SVS200) zinc, manganese, iron, copper, boron, and chloride

    The chart includes both the concentration of each nutrient and a bar graph showing whether that value is high or low. This chart is a large part of your soil fertility puzzle but it's not the whole picture. Just because you're high or low in a certain nutrient, doesn't mean that you have to go ahead and add it. There are more things to consider.

    Part 2 – Percent Cation Saturation and pH

    The second part is the percent cation saturation which shows the numerical percent of positively charged nutrients called cations and also a bar graph of these numbers.
    1. The most common soil cations are potassium (K+), magnesium (Mg++), calcium (Ca++) and sodium (Na+)
    2. Potassium should be 4–7 percent
    3. Magnesium should be 10–20 percent
    4. Calcium should be 65–75 percent
    5. Sodium should be less than 3 percent
    6. The balance left will be the percentage of hydrogen which is measured as pH

    If your calcium is low in the part 1 nutrient chart, adding high calcium fertilizer will also raise its cation saturation percentage and lower the percentages for the others including raising your soil pH.

    Part 3 – Electrical Conductivity (ECe)

    The next thing to consider is the ECe or the electrical conductivity of the soil. This is an indicator of how much salts are present. In this set of data, salts refer to more than sodium chloride, as that is just one type of salt. Here are some common salts found in soil:

    1. Magnesium sulfate
    2. Calcium sulfate (gypsum)
    3. Sodium bicarbonate
    4. Calcium chloride
    5. Potassium chloride
    6. Sodium sulfate

      Reasons Soils Become “Salty”

      There are many reasons that soils become “salty”.
      1. Adding lots of manures which are high in numerous kinds of salts
      2. Having a hard pan or poor drainage that prevents salts from washing out of the soil
      3. Having a high water table
      4. Irrigating with water that is high in minerals

        ECe is considered high when the value is above 2.0. High ECe will negatively affect crop yields. It restricts nutrient availability and negatively effects soil microorganisms.

        Part 4 – Cation Exchange Capacity (CEC)

        • CEC is one of the more important numbers on the report.
        • This measures the ability of the soil to hold onto and use nutrients that are present in the soil.
        • Ideally this number it would be 20 or more. If it is lower it will improve over time as you improve the overall soil health and quality.
        • Good CEC is found where soil health is excellent and is related to factors such as good microbial activity and organic matter content.

        When looking at your nutrient levels and deciding how much fertilizer to add consider your CEC level.

        Good CEC (20 or higher)

        • A good CEC will hold the nutrients in the soil so your plants can use them over an extended period of time.
        • It will also buffer your soil against changes in nutrients, so you will see a slow delayed effect when trying to correct any imbalances.
        • High CEC soils, fertilizers can be added all at once and fertilized less often.

        Low CEC (Less than 20)

        • Low CEC soil cannot hold on to the nutrients so when you fertilize.
        • Whatever your plants do not quickly use will be leached out of the soil.
        • It is like pouring fertilizers into a leaky bucket!
        • To fertilize a low CEC soil, you'll need to add small amounts of fertilizer, frequently, instead of trying to fix your nutrient levels all at once.

        Part 5 – Lime

        Excess lime is usually not a problem but if you have H in this box then you have high lime and it can be disastrous for the health of your garden. You've probably been adding too much calcium fertilizer if that's the case. If you have an L it means it's low and no corrective action is required. Lime is usually added in the form of high calcium fertilizers and high lime will also usually be reflected in a high calcium nutrient level as well as an alkaline pH which is a high pH (over 7.0)

        Part 6 – pH

        The pH reading is probably the most misunderstood reading. pH indicates the level of acidity or alkalinity in the soil.

        • A pH of 7 is neutral.
        • Above 7 it’s alkaline soil.
        • Below 7 it’s acidic soil.
        • Most plants prefer a slightly acidic soil between 6.0 and 6.8.
        • Some such as blueberries and azaleas like it even more acidic, in the range of 4.1 to 5.0.
        • Very few plants like a soil over 7.0, although some will tolerate it such as goji berries.

        While a change from an ideal 6.8 to a too alkaline 7.1 may not sound significant, it is actually a large jump in soil pH. It is not essential to get your pH exact because plants do have a range that they can tolerate but your soil pH must be within this ideal range for your plants to thrive.

        Effect of Poor pH Levels

        • Harmful to the beneficial microorganisms and bacteria in the soil.
        • Encourage disease-causing organisms that thrive at those levels.
        • If your soil pH is either too high or too low it'll have a negative effect on your plants even if the nutrients are in the soil, the plants will not be able to take them up.

        Correct your pH very slowly over a long period of time. Going back and forth between too acidic and too alkaline is worse for your plants than doing nothing at all.

        Now that we understand all the terms and definitions of the soil analysis report we can go on to step two, how to take care of any problems we might have. So enjoy you gardening experience and grow organic for life!

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