Stress Degree Days (SDD = Canopy Temperature - Air Temperature, Tc - Ta) measured around solar noon by infrared thermometry is an established thermal index used for precision irrigation scheduling.

• Irrigation scheduling: When canopy temperature exceeds air temperature due to stomatal closure, positive SDD values signal critical moisture stress requiring irrigation.
• Crop harvesting: Determined by physiological maturity, GDD, or grain moisture content.
• Recording of crop flowering: Governed by photoperiod and growing degree days (GDD).
• None of the above: Incorrect.

Karl Pearson's correlation coefficient 'r' is a normalized metric of linear association mathematically bounded strictly within the range [-1, +1].

• 0 and 1: Range for the coefficient of determination (r²) or probability, not correlation coefficient 'r'.
• 1 and 1: By Cauchy-Schwarz inequality, Pearson's 'r' always lies between -1 (perfect negative correlation) and +1 (perfect positive correlation).
• 1 and 0: Applies only to strictly negative relationships.
• None of the above: Incorrect.

Photosynthetically Active Radiation (PAR, 400-700 nm) is measured in terms of photosynthetic photon flux density (PPFD) using a specialized quantum sensor.

• Pyranometer: Measures total global solar radiation across the entire solar spectrum (300-3000 nm).
• Quantum sensor: Measures photosynthetically active radiation (PAR, 400-700 nm) in micromoles of photons per square metre per second.
• Precision pyranometer: Calibrated instrument for total broadband solar irradiance, not selective PAR.
• Piezometer: Hydrological instrument measuring water table hydraulic head.