Making Sense of Lab Data
You’ve gotten some numbers back from the soils lab – what now? As a student, researcher, farmer, or soils enthusiast you must convert and interpret these numbers into something meaningful. First, take a look at your numbers and see if they make sense!
Below is a data set for two soil types, followed by a further description of the samples and soil series. Take some time to review the values and determine if they match the soil description. Look for relationships between the soil properties and also how values compare for the mineral soil (Crescent) vs. the organic soil (Lumbum). Some things you might think about are:
- How do CEC and exchangeable/extractable cations relate?
- Why might values be higher for the Lumbum soil? Do other parameters give any clues?
- There is a significant difference in organic matter content between the two soils – can you see this reflected in other measures?
- These soils seem very different, but the electrical conductivity (EC) is the same – how can this be?
- How might pH affect the other values? Why are there 2 different pH measures and which one would you choose?
- What does “available” P mean and why might you measure it?
- How do the laboratory measurements complement the soil descriptions (e.g., texture, drainage)?
Examples of selected soil properties for two soil types commonly present in the Lower Fraser Valley, BC.
Calculating field values:
A common unit when talking about soil at the field-scale is kg per hectare. The concentration determined by lab analysis can be converted to these units if you have a soil bulk density value.
Example: Available P for Crescent soil, converting mg/kg to kg/ha
You need to know:
Bulk density for Crescent soil = 1.1 g/cm3 = 1100 kg/m3
Volume of one hectare furrow-slice that has depth of 15 cm = 1500 m3
Key things to remember when interpreting laboratory results:
- Relate your data back to your site characteristics.
- When doing further calculations and interpretation, remember to use the appropriate number of significant digits.