Resource use efficiency in agriculture

Light
1. Upper Limits of Food production
  1. Radiation use efficiency is the limiting factor
2. Principles of canopy structure
  1. Canopy structure determines (1) how much radiation is absorbed and (2) photosynthetic efficiency of the canopy as a whole
  2. Canopy light interception depends on
    1. Canopy size (surface area)
    2. Canopy geometry
  3. Natural systems are irregular and heterogeneous because of:
    1. Several interacting layers of different species occupying different niches down the canopy in time and space
    2. Large proportion of intercepting elements are non-photosynthetic
  4. The Extinction Coefficient (k) and Beer’s Law can be used to define canopy architecture and link f and L
  5. Leaf Area Index (L) and Fractional Interception (f) can be used to describe vegetation capture system and there is a functional relationship between f and L for different canopy architectures
  6. Complex and irregular canopies require more sophisticated techniques to be measured
3. Canopy structure and photosynthesis
  1. The higher the leaf area index the lower the the extinction coefficient (k) of the species / variety
  2. Upright canopies
    1. Disadvantage
      1. higher exposed ground resulting in water loss, ground evaporation and weed risk compared to flatter leaves that cover more ground.
      2. achieve canopy closure later
    2. Advantage
      1. Have more leaf area at a higher rate of photosynthesis
      2. higher productivity efficiency because there is a large sunlight area exposure
  3. By comparing light response curves at each point in the canopy we can determine the proportion of the canopy that is light limited or light saturated.
  4. Leaves with a low extinction coefficient for radiation can have a very high leaf area in a light-limited state and therefore a higher canopy photosynthesis rate - it doesnt saturate.
  5. Present
    1. Individual leaves display a curved response of photosynthesis to PAR – leaf response curve
    2. Canopies of vegetation display a generally linear response (`Conversion coefficient’) - integration of individual leaf curves
Radiation use efficiency
1. canopy photosynthesis is closely linked to radiation use efficiency (RUE)
2. Environment effectors
  1. Nitrogen
  2. Temperature
  3. Water
3. Photosynthesis determines how productive a crop can be thus It is the amount of light that a canopy intercepts that is most strongly related to biomass and yield potential.
4. Measuring
  1. 1. Measuring light response curves for individual leaves = controlled environment cabinet that is the first step to assess photosynthesis within a canopy
  2. 2. Measuring whole canopies in controlled-environments = allow us to control physical factors (temperature, CO2, humidity, soil moisture) whilst allowing leaves within a canopy of vegetation to interact as if in a natural environment
  3. 3. Measuring canopy responses in the real world = although it is not in a controlled environment it is in a more realistic situation
5. Conversion is required in order to adjust the biomass (g m-2) of a species for the chemical energy values (kJ g-1) of its different constituents (carbs, lipids and protein)

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Resource use efficiency in agriculture

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	Erstellt von Ibi Qemlas vor etwa 9 Jahre