Physiology and productivity of sugarcane with early and mid-season water deficit

An analysis of the physiological consequences of water deficit during the f irst half of the season on sugarcane productivity, can aid the evaluation o f yield expectations under rainfed systems and the opportunities for saving irrigation water early in the season. Four field experiments were conducte d at Ayr in the semi-arid tropics of Australia. irrigation was withheld at different stages of crop development to investigate timing and severity of water deficit on crop development, biomass accumulation and partitioning of biomass to millable stalk and sucrose, both during the season and at final harvest. Deficits imposed during the tillering phase, while having large i mpacts on leaf area, tillering and biomass accumulation, had little impact on final yield. This was primarily due to the length of time required to im pose significant water deficit when the canopy is small, the comparatively small amount of biomass accumulation lost through water deficit, and the ab ility of the crop to produce leaves and tillers at a rapid rate during subs equent well-watered conditions. On the other hand, water deficit imposed wh en the canopy was well-established (leaf area index >2) had a more deleteri ous impact on final yield of total biomass, stalk biomass, and stalk sucros e. Reductions in millable stalk biomass, could be solely explained by reduc tions in total biomass. Similarly, >97% of the variation in final cane or s ucrose yield could be explained by variation in stalk biomass. While there were transient effects of water deficit on stalk sucrose and dry matter con centration, significant impacts at final harvest did not occur until stalk biomass levels fell to ca. 50% of that of the well-watered control. (C) 199 9 Elsevier Science B.V. All rights reserved.