Soil Testing: How To Take Samples And Read Results

Agricultural productivity depends on the farmland quality, and a soil test can timely report a problem in crop growth conditions. Field suitability analysis helps choose the appropriate crops or decide on land use for farming.

Regular soil testing is ultimately important not only for growers but can provide valuable field insights to all agribusiness players, including agri-coops, crop insurers, banks, input suppliers, or commodity traders. Nonetheless, designated laboratories describe only the current field properties. So, while analyzing soil test results for decisions on field amelioration, it’s better to combine lab reports with historical data from satellite imagery analytics.

What Is Soil Testing?

It is the farmland analysis for multiple parameters like chemical content, toxicity, pH level, salinity, earth-dwelling biota, etc. Such tests also provide information on chemical contamination, humic or organic content, electric conductivity, cation exchange capacity, and other physical and chemical properties.

Types Of Soil Tests

The analysis type depends on the explored components or properties of the field ground that may beneficially or adversely impact crop development. The most frequently-used types analyze and measure:
  • mineral content,
  • pH level,
  • soil moisture,
  • salinity,
  • pesticides and chemical contamination,
  • structure and texture, etc.

Soil Nutrient Testing

Valuable information on nutrients content allows accurate fertilization to support plant needs within precision agriculture implementations. This is why the chemical test for soil nutrients is the most common.

Primarily, soil tests report on the content of nitrogen (N), phosphorus (P), and potassium (K), which are the most important nutrients for crops. Secondary nutrients to examine are calcium (Ca), sulfur (S), and magnesium (Mg). An extended test also includes minor elements like iron (Fe), manganese (Mg), boron (B), molybdenum (Mo), and others.

To test soil nutrient content, a sample is added to an extractant solution and mixed (typically by shaking). Then, the liquid content is filtered and analyzed for chemical elements’ presence and concentrations (converted to dry matter). The obtained number is the soil-test index .

Why is it important to test soil for nutrient levels? Availability of correct amounts of nutrients at certain phenological stages is vital for plants. A nutrient imbalance like nitrogen deficiency severely impedes plant growth, while high concentrations cause plant wilting, fertilizer burns, or abnormal development.

Soil Acidity Test (pH)

Proper pH in the field is essential for plant productivity, and either too high or too low pH will adversely affect crop growth. Testing pH of soil, one calculates its hydrogen ions. pH values may range from 0 to 14. The neutral value is 7, lower levels are for acidity, and higher than 7 mean alkalinities. Acidic or alkaline fields are treated correspondingly. For example, pH can be raised with lime, and an accurate pH test helps determine its required quantity.

How to test pH level in soil? Various kits allow measuring pH right in the field, but more accurate results are provided by state or private laboratories.

Soil Salinity Test

In saline fields, plants suffer from osmotic stresses due to poor water absorption. Soil salinity testing helps understand the suitability of lands for agricultural activities. Field salinity can be analyzed through:
  • evaporation of total soluble salts (TSS) from the ground-water extract;
  • measuring the electric conductivity (EC) of a saturated paste extract or a distilled water-earth dilution .
An electric conductivity soil test is performed in the field or a designated laboratory.
An EC soil test can also show the quantity of crop-available nitrogen in some non-saline lands.