Biomass accumulation in sugarcane: unravelling the factors underpinning reduced growth phenomena.

Constant radiation use efficiency throughout the entire sugarcane crop cycle is often assumed for crop yield forecasting and management purposes. However, several examples are known where the linear relationship between cumulative intercepted radiation and biomass accumulation becomes uncoupled at some stage, with the latter declining by 21% in one reported case. This slowdown in growth is commonly referred to as the reduced growth phenomenon (RGP). In certain instances, this phenomenon appears to be related to the timing of crop initiation and harvesting. Summer-initiated sugarcane crops do not always resume expected growth rates after the transition from winter to spring, despite conditions being favourable for vigorous growth. Possible factors underlying the failure of sugarcane crops to realize full yield potential are reported and interrogated in this review. The potential involvement of lodging, flowering, and tiller mortality have been reviewed and the data suggest that, while such factors may contribute, they are unlikely to be the major causes of sugarcane RGPs. Similarly, reports indicate that temperature cannot account for reduced growth, as rates remain low despite the onset of favourable conditions in spring. In contrast, a decline in specific leaf nitrogen, potential initiation of sugar-mediated source-sink feedback inhibition of photosynthesis, and increased rates of maintenance respiration that occur during sugarcane development and maturation appear to be likely factors contributing to RGPs. An evaluation of areas of sugarcane biology and agronomy that would benefit from further research towards overcoming yield restriction imposed by reduced growth phenomena is provided.