Yield accumulation in irrigated sugarcane. I. Effect of crop age and cultivar

Because the duration of growth for commercial sugarcane (Saccharum spp. hybrids) production can vary from 9 to 36 mo, determining the optimum age at crop harvest is important to profitability. To account for variable climate across seasons and locations, there is a need to understand the physiology of yield accumulation and quantitatively describe the effects of crop age on productivity. Few field studies have been conducted to determine the factors responsible for yield variation in different cultivars of sugarcane at different crop ages, and the physiology of yield accumulation has rarely been examined on a dry matter basis with all yield components, including tops, millable stalk, trash, and roots. This paper compares above- and belowground biomass accumulation with crop age in two current cultivars grown in field experiments under drip irrigation in Hawaii from 1991 to 1993, and reanalyzes earlier experiments conducted in Hawaii in the 1930s and 1940s to examine historical changes in the pattern of yield accumulation in sugarcane. The key findings from this analysis are that (i) differences in yield accumulation during the first 12 mo of growth were not necessarily reflected in final yields at harvest at 18 to 24 mo; (ii) yield accumulation was less efficient in the second year of growth for current cultivars, but not necessarily so for older cultivars; (iii) belowground biomass decreased from 17% of total biomass at 6 mo to 11% of total biomass from 12 to 24 mo; (iv) there was no indication that older cultivars were less productive than current cultivars; and (v) yields rarely increased beyond 18 mo of age