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Agronomy QUESTION #2112
Question 1
The concept of 'radiation use efficiency' (RUE) in crop production is defined as:
  • The ratio of photosynthetically active radiation (PAR) incident on the crop canopy to the total solar radiation received
  • The amount of above-ground dry matter produced per unit of intercepted photosynthetically active radiation (IPAR), expressed as g dry matter MJ⁻¹ IPAR — a key parameter linking canopy light interception to biomass production in crop simulation models✔️
  • The percentage of total solar radiation converted to grain yield (economic RUE)
  • The ratio of actual evapotranspiration to potential evapotranspiration under the current crop canopy
Correct Answer Explanation
RUE = Above-ground biomass (g) / Intercepted PAR (MJ). It is a conservative parameter for a species under non-stressed conditions: C3 cereals ~1.0–1.5 g/MJ; C4 crops (maize, sorghum) ~1.5–2.0 g/MJ. RUE is the slope of the linear biomass-IPAR relationship in Monteith's framework. Stresses (N deficiency, drought, heat) reduce RUE. Grain yield = RUE × IPAR × HI — making RUE central to yield analysis.