Calculating maximum theoretical yield in rice
Abstract Simple quantitative relationships can be useful in highlighting the characteristics that are key to taking yield towards its theoretical limit. Likewise, calculating maximum yields can be useful in suggesting attainable goals for plant breeders and agronomists. For this purpose we define how the core physiological drivers of yield combine to produce maximum yield. We make simplifications to produce three main equations that trace yield from solar energy through crop photosynthesis and biomass and then using harvest index to maximum grain yield. We focus our investigation on three types of canopy, taking as a starting point the C3 semidwarf elite rice cultivar IR72. We define an ideotype with a canopy of very erect leaves and large leaf area called Vela and consider it both as a C3 and a C4 photosynthetic canopy. We calculate the maximum daily photosynthetic rates and yields of the three canopy types for tropical and subtropical conditions. Owing to the effects of temperature on quantum yield and maintenance respiration, the conversion of photosynthate to shoot biomass is 40% larger in the subtropics than the tropics. In the tropics, the predicted maximum yields are 12.9 t ha −1 (semidwarf), 14.4 t ha −1 (C3 Vela) and the 17.9 t ha −1 (C4 Vela). In the subtropics those yields are: 20.1 t ha −1 , 22.4 t ha −1 and 25.0 t ha −1 , respectively. The key factors taking rice yields towards their ultimate limit are canopy architecture, quantum yield, maintenance respiration, and minimizing loss of photosynthetic capacity as lower leaves senesce and nitrogen is recycled to grain after peak photosynthesis has been reached.