YIELD ACCUMULATION IN IRRIGATED SUGARCANE .2. UTILIZATION OF INTERCEPTED RADIATION

Intercepted radiation is a major driving variable of crop production u nder high-input irrigated conditions. Quantitative information on the utilization of radiation in yield accumulation allows extrapolation be yond the current season and location, and when this information is inc orporated into crop growth simulation models, the effect of crop age o n the productivity of different cultivars can be examined under differ ent climatic conditions. This paper examines the differential performa nce of high-yielding sugarcane (Saccharum spp. hybrids) crops in terms of the amount of short-wave solar radiation intercepted (S-i) and the efficiency of use of intercepted radiation (RUE) in biomass productio n. Biomass accumulation during the 12- to 24-mo crop cycle was examine d for two experiments conducted in Hawaii, and three experiments condu cted in tropical Australia from 1991 to 1993. The analysis showed that (i) RUE was much less for growth after 12 mo than in the first 12 mo; (ii) maximum RUE. of sugarcane approaches 2.0 g MJ(-1); (iii) biomass accumulation beyond 12 mo was not-related directly to radiation utili zation; and (iv) cultivars differed in S-i, but differences in RUE cou ld not be unequivocally assessed due to the confounding effect of vari able recovery of trash in biomass estimates. It is concluded that stal l death and consequent biomass loss axe important factors contributing to yield variation in sugarcane crops growing for 12 to 24 mo, with a yield plateau occurring at variable crop ages during the second yeas of growth.