Soil testing assesses what soil nutrients are present or may be necessary for optimum plant growth and yield. Due to variability in soil across different regions, laboratory analysis, and reporting, guidelines very specific to your region may exist. A local agronomist can provide the information specific to your area. The soil test results list the concentration of each measured nutrient, an interpretation value (in low, optimum, and high), and recommendations for the amendments or nutrient application.
Typically, soil testing in the USA should be conducted every year or at least two out of three years. If you wish to monitor the nutrient levels over several years, it’s recommended that you take the samples at about the same time of year every time.
Source: Freepik
Soil Testing Interpretations:
Once you’ve collected your samples, you must send them in for analysis. Most US agricultural laboratories’ primary soil analysis package includes soil pH, extractable P, K, Ca, Mg, and micronutrients. Extractable nutrients are measured, and the magnitude of soil-test values may differ between laboratories; consistency is essential in the soil-testing lab. Variability between lab results can be attributed to several factors, including technique or extraction solution differences.
Interpretation of soil test results permits your nutrient levels to be placed into categories like low, adequate, or high based on the research and experience of the soil specialists. Recommendations are usually provided as pounds of fertilizer per 1,000 square feet. Ensure you understand the recommendations before applying the fertilizer; that is, determine whether the recommended amount of fertilizer is to be used in several separate applications or provided in one application.
What’s Included in any Soil Test Report?
The format of a soil test report will vary depending on where you get the test done, but the content itself is mostly the same regardless of where you go.
Here are the essential elements of any standard soil test:
- The amount of macronutrients- nitrogen (N), phosphorus (P), and potassium (K).
- The secondary macronutrients include sulfur (S), calcium (Ca), and magnesium (Mg).
- Micronutrients- copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), boron (B), chloride (Cl), nickel (Ni), and molybdenum (Mo) in the soil.
Other soil characteristics that may be covered in soil test results are organic matter (OM) content, soil pH, soluble salts (salinity), and cation exchange capacity (CEC).
Which Fertilizer Should I Use?
The easiest way to determine which nutrients your soil is lacking is by taking a soil sample for testing. Soil testing in the USA recommends the fertilizers needed for ideal plant growth. Soil tests also determine your soil pH and how much lime to apply, if any is required. Maintaining your soil pH is critical to ensuring that plants’ roots can take up the fertilizer you apply. Otherwise, you are wasting your time and money on fertilizer! Applying the correct amount also protects the environment from being polluted by excess nutrients. Soil tests should be done once a year for the first few years after planting anything new. After you have a couple of test results to compare from year to year, you can more easily predict future fertilizer needs based on your soil type.
How Do You Know How Much Fertilizer to Use When Looking at the Bar Graph?
Read the information below the bar graph under the heading “Recommendations.” Fertilizer and lime recommendations are customized for your soil sample based on the lab results reported in the bar graph. Keep in mind that these fertilizer recommendations are made on a per-year basis.
Why is Nitrogen Not Shown on the Bar Graph of the Soil Test Report?
Nitrogen recommendations are not based on a routine soil analysis. This is due to the many climatic, chemical, and biological factors that influence the amount of Nitrogen in the soil at any given time. Instead of soil analysis, nitrogen recommendations are based on research results from field experiments to determine the best application rate to attain optimum growing conditions for selected crops. All soil test reports provide standardized annual nitrogen recommendations based on current research.
What Nutrients Do Plants Need?
Out of the 18 nutrients known to be essential for plant growth, typically three are most often lacking in soils. These three nutrients are Nitrogen, phosphorus, and potassium, and every fertilizer product sold is required to have a guaranteed analysis of these nutrients in that order. The three numbers on the bag represent the percent of the total bag weight that contains these nutrients. For example, a 10-10-10 fertilizer contains a 10% of each nutrient by bag weight. So what’s in the rest of the bag? The remaining percentage is “filler,” which enables you to apply the fertilizer evenly over a large area. Each of these nutrients may be needed in different amounts depending on the types of plants you are growing and how your soil has been treated previously. Of all the nutrients, Nitrogen is the most limited and mobile in soils and must be reapplied annually.
Is More Fertilizer Better?
All fertilizer applications should be based on the amount of Nitrogen applied since this is the most essential nutrient. Nitrogen is also the easiest nutrient to misapply, and excess Nitrogen will increase over-growth, water demand, and plant susceptibility to insects and diseases. A good rule to follow is never applying more than 1 pound of Nitrogen every 1,000 square feet at any application. To quickly determine this maximum rate, you must divide 100 by the first number on a fertilizer bag (percent nitrogen). The result is the number of pounds of that product you’ll need to supply 1 pound of actual Nitrogen per 1,000 square feet. For example, if you use a 12-4-8 fertilizer, divide 100/12 = 8.3 pounds. Therefore, 8.3 pounds of 12-4-8 fertilizer would provide precisely 1 pound of actual Nitrogen over 1,000 square feet. Depending on the plant’s needs, this rate could be applied in every 4 to 6 weeks during a growing season.
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