Crops Flashcards
How much of land surface is managed for crops and pasture?
~40% - Foley et al., 2005
What are some the climatic factors that affect plant growth in a given location and the impact they have on the crop?
- Sesaonal rainfall patterns - length of growing season
- Intensity of rainfall - water requirement of crop
- Humidity - transpiration efficiency
- Temperature - rate of development of crop - higher = bad for total crop yield
- Day length (photoperiod) - timing of flowering
Give a way in which cropping systems can be matched to the climate
Day length - constant at equator - variable everywhere else
- Initiation of flowering is sensitive to daylength
- Hence flowering can be matched with the duration of rains to maximise water use and ensure lower soil moisture levels towards the end of the season - reducing the crop’s susceptibility to disease
- Can be affected by climate change
Give an example of a case study - matching cropping systems to climate
Rice:
- Upland/dryland rice: no standing water at any time - more stable yield
- Flood-prone; irrigated - common in valleys
Choice depends on rainfall, water storage, soil porosity, slope and different varieties of rice in each system
How can heat stress affect French maize? Hawkins et al., 2013
- Increasing importance of hot days in determining yield
- Decreasing importance of precipitation - because irrigation has increased
- Levelling off - could be due to increase number of hot days - or due to fundamental limit to plant yield
Summarise plant nutrients
- 17 essential nutrients
- Nutrients: Carbon, Hydrogen and Oxygen make up most of plant tissue (95%) - but are taken in from air and so are rarely limiting for growth
- Other 14 are taken up from soil - more likely to restrict growth if lacking
- 6 required in large amounts - Macroelements
- Other 8 required in small amounts - micronutrients
What are the 6 main macroelements?
Organic:
- Nitrogen - organic - must be fixed - cant get from atmosphere
Inorganic:
- Phosphorus - becoming scarce
- Potassium
- Calcium
- Magnesium
- Sulphur
What impact does agriculture have on the earth system?
Eutrophication:
- Nutrient enrichment of water - oxygen depleted in water = death of animals + algae blooms = water pollution
Synthesis of fertilizers:
- E.g., Haber-Bosch process - synthesis of ammonia - high temps + high energy - requires fossil fuels
How has our use of fertilizers and pesticides changed over time?
- Linear increase in both fertilizers and pesticides over time
- Intensification of use - may become unsustainable?
How much global GHGs come from food systems?
- 19-29%: mixture of Agriculture and land cover change - deforesting to crow crops / cattle
How are crop and the climate modelled?
Coupled crop-climate models:
- Can use offline crop models to assess impact of climate on crops
- Or, to understand feedbacks from crops onto weather and climate - need to couple the processes
- May also be impact of coupling on yield - e.g., capture diurnal cycle better and its influence on crops (e.g., temp/precipitation)
How has the change in suitability of land for agriculture changed over time?
- Central USA, Europe, Middle East, deserts in Africa and northern Australia have become less suitable
- But northern - high latitudes have become more suitable - northern Russia, Canada, Scandinavia etc
- But overall: the increases we are seeing are in the land that is marginally/moderately suitable and the increase in highly suitable is only very small
How is using water an unsustainable practice?
- ‘Mining’ water from aquifers is considered a non-renewable resource
- Unsustainable agriculture irrigation is different in different parts of the globe
How can extreme events affect crops - give example?
Extreme high temps:
- T>34 degrees - threshold for rice - even a few days above can be detrimental - reduce yield
- These large climate events that affect yield can then have a massive impact on price - biophysical and socioeconomic impact
What is time of emergence climate signal and how can it be modelled?
- 21 CMIP5 models, all 4 RCPs
- Calculate precipitation change in time in ensemble and uncertainty due to inter-model spread and inter-ensemble member spread
- Time of emergence (ToE): time at which the signal of climate change emerges from the noise of natural variability - key variable for climate predictions
- Look to see when climate has changed - and see impact on each major crop: Wheat, Soybean, Rice, Maize - tells us when the crops will be grown out of the environment they are used to
- And whether we can keep up with this process - tells us that crop breeding is not keeping pace with climate change
