ASRB ARS / NET / SMS / STO Climate Change Impacts on Agriculture & Food Systems: practice questions

1 · Temperature, heat stress and crop phenology · easy

A maize crop experiences Tmax = 32 °C and Tmin = 18 °C on one day. Using the simple averaging method with a base of 10 °C and no upper cap, how many growing degree days accumulate?

1. 7
2. 14
3. 25
4. 15

2 · CO2 fertilisation, C3 and C4 responses and nutritional quality · hard

Why did FACE experiments give smaller crop yield increases from elevated carbon dioxide than earlier enclosure studies?

1. Enclosures altered microclimate, rooting and light, inflating responses that FACE avoided
2. Enclosures measured biomass only, and biomass never increases under elevated carbon dioxide
3. FACE plots received less carbon dioxide than their target, so the true response was never measured
4. FACE used only C4 crops, which respond weakly, whereas enclosures used only C3 crops throughout

3 · Climate and pests, diseases and weeds · hard

In a maize field, rising carbon dioxide alone would be expected to favour which weeds most?

1. C3 broadleaf weeds, because their photosynthesis responds to CO₂ more than the C4 crop does
2. Parasitic weeds only, because they draw extra CO₂ directly from the host crop's vascular system
3. C4 grass weeds, because their photosynthesis responds to CO₂ much more than C3 plants do
4. No weeds, because elevated CO₂ suppresses germination of all weed seeds in the soil seed bank

4 · Livestock heat stress and feed availability · hard

Using the NRC (1971) formula THI = (1.8T + 32) − (0.55 − 0.0055RH)(1.8T − 26), with T in °C and RH in per cent, compute the THI for a dairy shed at 32 °C and 60 per cent relative humidity.

1. 72.2
2. 88.3
3. 89.6
4. 82.6

5 · Sea-level rise and salinisation of coastal farmland · medium

Using the Maas–Hoffman model Yr = 100 − b(ECe − a) with FAO-29 values for rice, a = 3.0 dS m⁻¹ and b = 12 per cent per dS m⁻¹, what relative yield is expected at ECe = 6 dS m⁻¹?

1. 64 per cent
2. 36 per cent
3. 79 per cent
4. 28 per cent

6 · Sea-level rise and salinisation of coastal farmland · medium

Using the Maas–Hoffman model Yr = 100 − b(ECe − a) with FAO-29 values for wheat, a = 6.0 dS m⁻¹ and b = 7.1 per cent per dS m⁻¹, what relative yield is expected at ECe = 9 dS m⁻¹?

1. 36.1 per cent
2. 78.7 per cent
3. 21.3 per cent
4. 28.0 per cent

7 · Methods: field experiments, FACE, statistical and process models · easy

What is the 'chamber effect' in open-top chamber experiments?

1. The noise made by chamber fans, which is known to slow the growth of seedlings
2. The effect of a chamber's colour on the flowering date of plants nearby outside
3. The release of CO₂ by chamber walls as they age in sunlight over several seasons
4. Altered temperature, humidity and wind inside that confound the treatment

8 · Methods: field experiments, FACE, statistical and process models · medium

Why are late or staggered sowing dates used as a low-cost experiment on heat effects, and what is their drawback?

1. Later sowing exposes crops to hotter periods, but day length changes too
2. Later sowing removes all pests, but it needs the crop to be grown in sealed chambers
3. Later sowing exposes crops to more CO₂, but it requires an expensive enrichment ring
4. Later sowing doubles the rainfall received, but it cannot be done for any cereal crop

9 · Methods: field experiments, FACE, statistical and process models · medium

What is the main advantage of field infrared heaters over enclosures for warming experiments?

1. They warm only the soil, so above-ground processes are left completely unchanged
2. They have no side effects, perfectly reproducing future climate in all respects
3. They raise carbon dioxide at the same time, so two factors are tested at once
4. They warm the canopy in the open without altering wind and light by enclosure

10 · Crop simulation models for impact assessment · easy

What is the minimum set of daily weather inputs needed by most crop simulation models?

1. Maximum and minimum temperature, rain and solar radiation
2. Soil pH, organic carbon and bulk density only
3. Monthly mean temperature and the annual rainfall totals only
4. Wind speed, cloud type, air pressure and sunshine colour