Research Methods
About Earthworm Biomass Calculations
More about the biomass calculation spreadsheet
There are several steps in the calculation for determining AFDgrams of biomass of your earthworm. The first is to calculate the natural log (LN = e = 2.7182818) of the length measurement, then by putting that value into the equation below, you calculate the natural log value of the earthworm’s biomass:
LN(biomass) = [2.2853 x LN(length)] – 11.9047
Finally, to convert the LN(biomass) value back to a more useable unit (AFDgrams of biomass) reverse the process of taking the natural log we used above by finding an exponent for the value of LN (e = 2.7182818) that equals the calculated LN(biomass) value, and that exponent if the “calculated AFDgrams of biomass”. For example, in the first row of our example spreadsheet …e0.005 = -5.30
Confused?! That’s why it’s nice to have mathematicians and computer spreadsheets that help us make all these complex calculations!
To make the calculations manually
- Measure the length of your preserved earthworms to the nearest millimeter (mm).
- Using a calculator or spreadsheet, find the natural log of the earthworm length measurement. In this example, ln(50) = 3.91.
- Insert the natural log of the length into the allometric equation:
ln(AFDB)=[2.2853xln(length)]-11.9047
In our example, ln(AFDG) = (2.2853 x 3.91) – 11.9047. So the natural log of the earthworm’s ash-free-dry biomass is ln(AFDG) = -3.14.
To convert the ash-free-dry biomass value back to a more familiar form (grams), you “exponentiate the natural log” with ln(AFDG), which is fancy lingo for raising the value of the natural log (2.7182818) to a power equal to your ln(AFDG). Stick with me here…
In our example, where the natural log of the earthworm’s ash-free-dry biomass is… ln(AFDG) = -3.01; you would raise 2.7182818 to the power of -3.01 to get ash-free-dry grams of earthworm, like this…
2.7182818^(3.14)= 0.043 AFDgrams of earthworm biomass