12.3 Agricultural production

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Solar radiation is linked to agricultural productivity via biomass production and allocation to harvested parts (e.g. grain). Radiation is considered here only in relation to canopy photosynthesis. Biomass is obviously derived from photosynthesis, but is less than total carbon assimilation due to a large respiratory loss (see Case study 12.2). Carbon lost via respiration is a fairly constant proportion of photosynthesis, and thus variation in canopy photosynthesis is sufficient for present purposes to explain variation in biomass. How then does interception of photosynthetically active radiation (PAR) affect biomass production and allocation to crop yield? Three steps are considered: (1) variation in incident PAR during crop growth, (2) interception of PAR by a crop canopy and (3) efficiency of PAR conversion into biomass and yield.