ICAR AICE-JRF/SRF Soil Organic Carbon & Carbon Sequestration: practice questions

1 · Soil carbon pools and turnover · medium

Which description of mineral-associated organic matter (MAOM) is correct?

1. Charcoal particles from fires that make up most of the carbon in every agricultural topsoil
2. Fresh fragments of roots and straw that decompose within a single growing season in all soils
3. Living earthworms and fungi, which together hold most of the soil's organic carbon at any time
4. Small organic molecules bound to fine mineral particles, persisting for decades to centuries

2 · Practices that build soil carbon: residues, cover crops, reduced tillage, grazing, agroforestry · medium

Which practice usually gives the largest SOC gain per hectare on former cropland?

1. Applying lime to correct acidity
2. Switching from mouldboard to chisel plough
3. Removing all straw for bedding
4. Conversion to permanent grassland or forest

3 · Saturation, equilibrium and the time course of sequestration · medium

Using Hassink's (1997) equation C_sat = 4.09 + 0.37 x (% particles < 20 micrometres), what is the maximum fine-fraction carbon for a soil with 40% of particles below 20 micrometres?

1. 4.24 g C/kg
2. 18.89 g C/kg
3. 14.80 g C/kg
4. 178.4 g C/kg

4 · Permanence and reversal risk · medium

Why are soil carbon losses after disturbance often faster than the earlier gains?

1. Losses are counted twice in national inventories, which doubles their apparent speed
2. Disturbance raises the decay rate at once, while gains depend on slowly accumulating inputs
3. Losses are measured in CO2 while gains are measured in carbon, which makes losses look larger
4. Gains require nitrogen fixation by every soil microbe, which takes centuries in all climates

5 · Soil carbon models: RothC, Century/DayCent · easy

Which set lists the pools of the RothC model?

1. Active, slow and passive only
2. POM, DOC, CO2 and CH4
3. Leaf, stem, root and grain
4. DPM, RPM, BIO, HUM and IOM

6 · Soil carbon models: RothC, Century/DayCent · medium

What does DayCent add to the Century model?

1. A daily time step and simulation of trace gases such as N2O and methane
2. A laboratory protocol for dry combustion of soil carbon samples
3. A monthly time step and the removal of all nitrogen and phosphorus cycling
4. A purely statistical approach that replaces all process descriptions

7 · Soil carbon models: RothC, Century/DayCent · medium

Which long-term experiment, begun in 1843, has been central to developing and testing the RothC model?

1. Broadbalk at Rothamsted
2. Sanborn Field in Missouri
3. Askov in Denmark
4. Morrow Plots in Illinois

8 · The 4 per 1000 initiative and national soil-carbon programmes · medium

Which is NOT a standard scientific criticism of treating 4 per 1000 as a literal global target?

1. Building SOC needs nitrogen and phosphorus
2. Gains slow over time and can be reversed
3. Many soils are already near their equilibrium or saturation level
4. Soil carbon cannot be measured by any laboratory method

9 · The 4 per 1000 initiative and national soil-carbon programmes · medium

Which FAO-hosted partnership produced the Global Soil Organic Carbon Map (2017)?

1. The Global Methane Pledge
2. The Adaptation Fund
3. The Global Soil Partnership
4. The Green Climate Fund

10 · Inorganic carbon and enhanced rock weathering · medium

Why is CO2 capture by weathering of carbonate rock regarded as only temporary, unlike silicate weathering?

1. Carbonate weathering produces methane, which escapes from the soil within days
2. Carbonate rocks contain no calcium, so no bicarbonate can form
3. Carbonate weathering happens only in deserts, where no water exists
4. Over ocean timescales carbonate precipitation releases the CO2 again