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
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