12 Soil Carbon and Respiration
Soil respiration is the net release of CO2 from all living organisms in the soil, including bacteria, fungi, protists, earthworms, plant roots, etc. The rate of soil respiration has many different applications. It can be used assess soil health, with higher respiration rates indicating a more active, and thus healthy microbial community. It can also be used as part of a C balance to determine if soil under particular management practices is a net source or sink of C, which has direct application to carbon credits. Respiration rates can also be influenced by the quality of the substrate being consumed by the soil microbes. In this lab you will conduct tests to determine the relative soil health of two soils that have been managed differently for over a decade. The tests include a CO2 burst or a basal respiration test to determine the relative respiration rates, and a slake test to determine the stability of the soil aggregates. You will also work with your classmates to complete the Carbon Cycling problem set.
Learning Objectives
- Define soil health.
- Describe how soil health indicators are used to track changes in soil health over time.
- Describe how soil health indicators are used to compare two different management practices.
- Explain how soil organic matter influences aggregate stability.
- Perform carbon cycle calculations for a Kansas farm.
Materials
- Two or more soil samples that have been oven-dried at 35-40°C (for the CO2 burst test)
- Two or more moist soil samples that have been recently collected (for the basal respiration test)
- Soil roller
- 30 cc (cm3) soil scoop and striker rod
- Plastic beaker
- Mesh screen
- Pipette set to 9 mL
- Water
- Solvita® CO2 burst test paddle
- Test jar with lid
- Solvita® low-CO2 test paddle
- Incubator (optional)
- Solvita® Digital Color Reader and/or reference color charts
- Two or more soil peds that are approximately the size of a golf ball
- Coarse wire mesh or machine cloth
- Two, 1 L sedimentation columns
- Soil Carbon Cycling Problem Set
Recommended Reading & Viewing
- Soil Respiration Overview (CropWatch – Youth, 2013e)
- Soil Health Demonstration: Slake Test (Montana NRCS, 2020)
- Soil Respiration (USDA-NRCS, 2009)
- Soil Respiration (USDA-NRCS, 2014b)
- Solvita® Soil CO2 Respiration Updated Protocol Improvement (Woods End Laboratory, 2019)
Prelab Assignment
Using the recommended reading and videos and the introduction to this lab, consider the questions listed below. These definitions/questions will provide a concise summary of the major concepts addressed in the lab. They also useful study notes for exams.
- Define soil health
- Define soil respiration
- Define carbon sequestration.
- Name three ways in which C is lost from the soil.
- Which of those three losses of C from the soil is the most significant?
- What practices might reduce or even reverse this loss in soil C, and thus maintain or improve soil health?
- Describe how soil organic matter impacts