LFL: Soil Carbon Laboratory Incubation
Soil cores are taken at 10 areas per plot at a depth of 10 cm usually after tillage. One step forward is taken in the row and the core is sampled from the resulting footprint. Five soil cores (1.9 cm diameter cylinder wet tip hand probe) are taken in a zigzag pattern up between rows 2 & 3 and five soil cores are taken in a zigzag pattern down between rows 4 & 5 using the footprint method. The cores are taken on either side of the row. The cores are placed directly into a plastic zip lock bag and placed on ice in a cooler.
The soils are immediately taken to the laboratory and placed in a cooler at 4 ° C until analysis can be performed.
The composite soil samples are mixed, sieved through a 6 mm sieve and sub-sampled for carbon mineralization determination. The sub-samples are allowed to air dry and then placed in a plastic bag for further analysis and/or storage.
For carbon incubations, 50 g are weighed into a plastic specimen cup and adjusted to 70% water holding capacity. The cups are placed in quart size wide mouth canning jars, 10 ml of water added to the bottom of the jars (to maintain humidity) and then sealed with the accompanying ring/lid. The lid has a holed drilled in the center and a septa placed in the hole to accommodate gas sampling.
The jars are pre-incubated in a darkened controlled temperature room at 25 ° C for 5-7 days. The CO2 content in the headspace of each jar is measured at various timed intervals using an infrared gas analyzer. The jars are flushed with CO2-free air when CO2 concentrations are expected to exceed 6% prior to the next sampling.
Reference: Assessment Methods for Soil Carbon. 2001. Chapter 14. Lal, R., Kimble, J. and Follett, R. (eds). CRC Press Boca Tatton, FL.