Know Your Soil
It's really important to understand what your soil needs before starting a fertilizing program. If you apply amendments without knowing your soil’s nutrient levels, you may be wasting money on fertilizers. The most thorough test is a professional Complete Soil Analysis, which provides a detailed breakdown of your soil’s composition. This will be the focus of our video and blog.
So, get out your soil test results and your booklet, Understanding Your Soil Analysis Report, and follow along to learn how to interpret your results.
Part 1 – Chart of Nutrient Levels
At first glance, your soil test report might look like a collection of overwhelming numbers and ratios, but these values are interconnected and should be considered together when determining soil fertility needs. The first key section to examine is the nutrient levels chart.
On this chart, you’ll find:
- Percent organic matter
- Macronutrients – nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur
- Trace minerals (if you opted for the Complete Soil Analysis-SVS200) – zinc, manganese, iron, copper, boron, and chloride
The chart provides both the concentration of each nutrient and a visual representation of whether levels are high or low. However, just because a nutrient appears low or high doesn’t necessarily mean you need to adjust it. There are other factors to consider.
Part 2 – Percent Cation Saturation and pH
The second part of the report is the percent cation saturation, which shows the numerical percentage of positively charged nutrients, or cations, in your soil. These are essential for soil fertility and plant uptake.
The most common soil cations are:
- Potassium (K+) – should be 4–7%
- Magnesium (Mg++) – should be 10–20%
- Calcium (Ca++) – should be 65–75%
- Sodium (Na+) – should be less than 3%
The balance left over is the percentage of hydrogen (H+), which is measured as pH. If calcium levels are low in the nutrient chart, adding high-calcium fertilizer will increase cation saturation and raise soil pH.
Part 3 – Electrical Conductivity (ECe)
Another key measurement is ECe, or electrical conductivity, which indicates the amount of salts in the soil. Excessive salt buildup negatively impacts soil structure, reduces nutrient availability, and harms soil microbes.
Common salts found in soil include:
- Magnesium sulfate
- Calcium sulfate (gypsum)
- Sodium bicarbonate
- Calcium chloride
- Potassium chloride
- Sodium sulfate
Soils become “salty” due to factors such as excessive manure application, poor drainage, a high water table, or mineral-heavy irrigation water. An ECe above 2.0 is considered high and can restrict plant growth.
Part 4 – Cation Exchange Capacity (CEC)
Cation Exchange Capacity (CEC) is one of the most important values on your soil test. It measures your soil’s ability to retain and supply nutrients to plants. Ideally, a CEC of 20 or higher is best for maintaining soil fertility.
- Good CEC (20 or higher): Nutrients are held in the soil longer, reducing the need for frequent fertilization. This also buffers the soil against drastic changes in nutrient levels.
- Low CEC (Less than 20): Nutrients do not stay in the soil, leading to nutrient leaching. In this case, fertilization should be done in smaller, more frequent applications rather than in one large dose.
Part 5 – Lime
Excess lime in soil is typically not an issue, but if your soil test shows an "H" in the lime box, it means you have high lime, which can harm plant growth. High lime is usually caused by excessive calcium fertilizer applications and is often reflected by an alkaline soil pH (above 7.0).
If your test shows an "L," lime levels are low, and no corrective action is needed. Lime is commonly added using calcium-based soil amendments, but excessive lime can raise pH beyond optimal levels.
Part 6 – pH
Your soil pH reading indicates whether your soil is acidic, neutral, or alkaline:
- pH of 7 is neutral
- Above 7 is alkaline
- Below 7 is acidic
Most plants thrive in slightly acidic soil between 6.0 and 6.8. Some plants, like blueberries and azaleas, prefer even more acidic soil (4.1 to 5.0). Very few plants tolerate alkaline soil above 7.0, though some, like goji berries, can adapt.
Even a slight pH shift, such as from 6.8 to 7.1, represents a significant chemical change. While plants can tolerate a range, maintaining optimal pH ensures nutrient availability. If soil pH is too high or too low, plants may struggle to absorb essential nutrients—even if those nutrients are present in the soil.
Effects of Poor pH Levels
- Disrupts beneficial soil microbes and bacteria
- Encourages disease-causing organisms
- Restricts nutrient uptake
If pH correction is necessary, make adjustments gradually over time. Rapid fluctuations between acidic and alkaline conditions can harm plants more than a stable but imperfect pH.
Now that you understand the key parts of a soil test report, you can take the next step—correcting any imbalances to improve your soil’s long-term health. Enjoy your gardening experience and grow organic for life!
