Soil Respiration

Question 1

What is soil respiration?

Answer 1

a measure of biological activity and decomposition

it is the rate of CO2 released

Question 2

How does respiration work?

Answer 2

while SOM is decomposed, the organic nutrients contained in OM (ex. P, N, S) are converted into inorganic forms that are available to plants = aka mineralization

respiration is also called carbon mineralization because of this

Question 3

What is the other name for soil respiration?

Answer 3

carbon mineralization

Question 4

What are the steps of respiration?

Answer 4

plants draw CO2 from the air and H2O from the soil to make carbs

carbs are exuded by plant roots to feed soil organisms

carbon-rich soils hold more water

soil organisms die and release CO2

plants absorb the CO2 released by dead organisms being decomposed

plants produce oxygen

cycle begins again

Question 5

*4 sources of CO2?

Answer 5

1. Microbial respiration:
   the aerobic decomposition of SOM to obtain energy for their growth
2. plant roots
3. faunal respiration
4. dissolution of carbonates in soil solution (ie. concrete)

Question 6

Define soil respiration vs. microbial respiration?

Answer 6

Soil respiration is from ALL living organisms

microbial respiration is only from soil microorganisms

Question 7

What are 3 reasons soil respiration is so important?

Answer 7

1. it is an indicator of soil health and it reflects the capacity of a soil to support life
2. describes the level of microbial activity, SOM content and its decomposition
3. an indication of nutrient cycling - the conversion of nutrients in OM into inorganic forms available to plants

Question 8

6 factors that affect respiration?

Answer 8

1. biologically activity varies daily and seasonally
2. climate: temperature and precipitation have a big impact on microbial activity
3. sandy and silty loams have favourable respiration rates (high porosity, good aeration, high available water capacity)
4. in clay soils, much of the SOM is protected from decomposition by clay particles and colloids that limit respiration and mineralization of N
5. sandy soils have low SOM and low water availability which can limit soil respiration and mineralization of N
6. moisture: respiration will increase with moisture, but saturation will slow microbial activity

Question 9

T or F: Soil respiration occurs best at 60% or less water-filled pore space

Answer 9

True, once over 60%, pores are too saturated and not enough space for oxygen

Question 10

At which percentage of water-filled pores does respiration become denitrification?

Answer 10

after 80% water-filled pores soil respiration will decline to a minimum level and most aerobic organisms will begin denitrifying NO3 instead of O2

Question 11

What are the negative impacts of flooded or saturated soils?

Answer 11

incomplete mineralization of SOM can occur resulting in the formation of compounds that are harmful to plant roots (ex. methane and alcohol) - this will affect plant respiration which can kill plants

Question 12

What processes will occur if soils become flooded/saturated and cannot respire O2?

Answer 12

Denitrification and sulphur volatilization will occur which can cause GHG emissions and acid deposition

Question 13

T or F: a soil microbiome exists in healthy soils because there is a massive amount of CO2 being released from healthy soils, but most of it will be taken back in through the plants

Answer 13

TRUE

Question 14

When does excessive respiration and OM decomposition occur? why? does this create a stable or unstable system?

Answer 14

occurs after tillage due to the destruction of aggregates that previously protected SOM and increased soil aeration
creates an unstable system

Question 15

What does a low respiration rate indicate?

Answer 15

that there is little or no SOM and therefore little or no microbial activity

can also indicate that the soil properties that contribute to respiration (ex. temperature, moisture, aeration) are limiting biological activity and SOM decomposition

Question 16

What does a low N level, but a high respiration rate indicate?

Answer 16

the N is being immobilized like for example when there is an addition of residue with a high C:N ratio

Question 17

What are 7 causes of low respiration rates?

Answer 17

too much water
low porosity
not enough water
depleted SOM
too much SOM
reduced soil aggregation = compaction or tilling
limited nutrient availability

Question 18

T or F: in favourable conditions, the rate of respiration is always limited by the supply of SOM

Answer 18

TRUE

Question 19

3 management techniques to avoid low respiration rates?

Answer 19

1. excessive tilling or burying residue
2. removing residues
3. applying high N fertilizers (speeds up SOM loss)

Question 20

• 10 practices that can improve SOM (and indirectly improve respiration)

Answer 20

1. conservation tillage/no till
2. consistent application of manure and other OM
3. diverse crop rotations with high residue and deep roots
4. leaving behind crop residue
5. cover crops
6. maintaining living roots
7. irrigation in dry conditions or drainage in wet conditions
8. controlled traffic movement - limiting compaction
9. managing pH and soil salinity
10. avoiding fertilizers that kill microbes

Question 21

What are the 3 ways we can measure soil respiration?

Answer 21

1. Draeger-tubes
2. automated chamber systems
3. Solvita colour tests

Question 22

T or F: there is more CO2 in soil air than there is in the atmosphere?

Answer 22

TRUE

Question 23

3 reasons maintaining soil health is so important for sequestering carbon?

Answer 23

1. respiration of CO2 is a direct measure of soil biological activity
2. crops consume large quantities of CO2 daily
3. soil produces and releases an amount of CO2 that is comparable to how much it takes in