Decline in the growth of a sugarcane crop with age under high input conditions

In Australian sugarcane crops, growth in terms of radiation use efficiency (RUE) can appear to slow down well before final crops are harvested, despite conditions that are considered favourable for growth. In order to assess the extent and cause of this reduced growth phenomenon (RGP), 14 experiments conducted in Australia were examined. From these experiments, 34 treatments were selected where nutrients and water were likely to be non-limiting and consequently the yields obtained were likely to be limited only by temperature and radiation. Radiation use efficiency is defined as the measured amount of net biomass accumulated above ground per unit radiation intercepted. Accumulated biomass may have been lost through loss of stalks. In almost half of the treatments RUE significantly declined between approximately 223 and 665 days after crop start. The high incidence of RGP found in the analyses (a) challenges the previously held assumption that a constant value of RUE can be used to adequately describe biomass accumulation in sugarcane as a function of cumulative radiation interception and (b) suggests that relatively low growth rates during the later phases of the cropping season are frequently experienced throughout the Australian sugar industry. Reduced growth phenomenon resulted in actual biomass at final harvest being on average 21% less than potential yield, compared with 5% in crops that did not display a slowdown in growth. Mean maximum RUE in the plant crop was greater than in ratoon crops, at 1.37 and 1. 19 g MJ(-1), respectively. As there was no effect of location, cultivar, crop duration, ratoon crop class or fumigation treatment on RUE for the periods either before or after the onset of reduced growth, it would appear that the value of RUE is predominantly influenced by crop class. Despite the differences in RUE between the two crop classes, RGP occurred at a similar frequency in both plant and ratoon crops. In order to gain a greater mechanistic understanding of the factors likely to be associated with the onset of the RGP, the relative time of lodging, specific leaf nitrogen (SLN), number of stalks and seasonal temperature were all considered individually. Whilst declining SLN and increasing stalk loss were associated with reductions in growth during the later periods of crop growth, it is likely that lodging also contributed to the widespread slowdown in biomass accumulation, whereas photosynthetic stress, as a result of extreme temperatures, did not play a substantive role in reducing growth. (c) 2005 Elsevier B.V. All rights reserved.