AGRI 31

• Phenotype = Genotype (G) + Environment (E) + (G x E)
• Genotype (G)


  Sets the limits for the phenotype
• Environment (E)


  Modifies the expression of the phenotype
• Yield = genetic factors + environmental factors + (GxE)
• Environmental Factors


  • Abiotic
  • Biotic
• Abiotic factors


  • Climatic (climate, weather)
  • Edaphic/Soil factors
  • Climatic stresses (drought, salinity, acidity, lahar, La Niña, El Niño, greenhouse effect, global warming)
• Biotic factors


  • Beneficial organisms (pollinators, decomposers, natural enemies)
  • Pests (arthropods, pathogens, weeds, vertebrate pests)
  • Allelopathy
• Climate


  The long-term weather pattern of an area, including temperature, precipitation, and wind or weather averaged over long period of time (seasonal pattern)
• Weather


  The atmospheric conditions in any area at any time, with regards to sun, cloud, temperature, wind and rain, etc. (deviation from pattern)
• "Climate is what you expect, weather is what you get"
• Components of climate


  • Sunshine
  • Temperature
  • Wind movement
  • Precipitation
  • Relative Humidity
  • Mist
  • Fog
• Climate is a major determinant of geographic distribution of natural vegetation and cultivated crops
• Climatic Factors


  • Solar radiation
  • Temperature
  • Wind movement
  • Precipitation
  • Relative Humidity
  • Mist and Fog
• Solar radiation


  Most important in agriculture
• Aspects of irradiance


  • Intensity (foot candles or lux)
  • Duration or daylength (hours/day)
  • Wavelength (Angstroms or nanometers or identified by its color)
• Biological window of light

  Biological effects
• Electromagnetic radiation spectrum of biological importance
• Photoenergetic effect


  Direct effect on Photosynthesis
• Photocybernetic effect


  Effect on development of plants
• Total Dry Matter correlated to intercepted radiation
• Light received above light compensation point affects growth and development
• Not all wavelengths are equally effective: Photosynthesis- red and blue, Photoperiodism- far red and red
• Solar constant


  Amount of solar radiation that reaches the outer limits of the earth's atmosphere
• Solar constant = 2.0 cal/cm2/min (15% fluctuation within the year)
• PAR


  Photosynthetically active radiation used by plants to fix CO2 during Photosynthesis
• Classification based on light intensity requirements

  • Heliophytes – sun-loving
  • Sciophytes – shade loving
• Albedo


  Reflected radiation/total incident light, reflects how fast and what degree surface is heated
• Albedo - 50-60% in polar regions, 20-30% in tropical equatorial regions, 80% reaches ground in the absence of cloud cover
• Daylength


  Varies with latitude, different between day and night and increases as latitude from equator increases
• Flowering and germination are affected by daylength
• Photoperiodism


  Plant response as conditioned by daylength
• Photoblastism


  Germination response with respect to daylength
• Classification of plants based on daylength

  • Short day plants
  • Long day plants
  • Day neutral
• Temperature


  Important in every chemical, physiological and biochemical processes in plants
• Temperature requirements


  • Minimum T- below which reaction = 0
  • Optimum T – reaction = maximum
  • Maximum T – above which reaction = 0
• Temperature depends on solar radiation, surrounding land masses/bodies of water, altitude - 0.6 decrease in temperature per 100m rise in elevation
• Classification of crops based on temperature requirement

  • Cool season- cole crops
  • Warm season- rice, banana
  • Tropical- coconut
  • Sub-tropical- citrus
• Temperature requirement for


  • Flowering – vernalization
  • Crop maturation
  • Germination
• Degree day


  Measurement of departure of the daily mean temperature above the minimum threshold temperature for the plant (base temp)
• GDD or heat units


  ∑ DT – BT