Response of Drip‐Irrigated Sugarcane to Drought Stress1

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Abstract
Though drip irrigation is used on more than half of the irrigated sugarcane (Saccharum spp. hybrid) in Hawaii, the effects of drought stress on the growth and yield of drip‐irrigated sugarcane has not been investigated extensively. This study reports the effects of a single period of drought stress on the growth and metabolism of cultivar H62‐4671 during vegetative growth in drip‐irrigated fields during the 1st year of a normal 2‐year crop in five fields at Kekaha Sugar Company, Kauai, Hawaii. The plants ranged from 5.4 to 9.8 months of age at the beginning of the experiment.Water depletion from the soil profile, leaf water potential (ψΙ), leaf solute potential (ψΠ), leaf pressure potential (ψρ), stalk elongation, plant sugar, K, and amino acid concentrations were monitored at 1200 to 1400 hour during a 5‐ or 6‐week period of drought stress. In three of four fields, soil water extraction was limited by low soil water content after cumulative profile water depletion of approximately 120 mm.Stalk elongation was strongly correlated to ψΙ and cumulative soil water depletion. Stalk elongation of plants in drought‐stressed plots was less than 80%' that of plants in well‐watered plots after only 50 mm of cumulative soil water depletion. During drought the concentrations of potassium and reducing sugars in the leaf blade increased, but the concentrations of sucrose and free amino acids changed little. None of these metabolites changed in the stem apex.The results indicate that a serious reduction in stalk elongation occurs prior to a reduction in the rate of soil water depletion, a change in the false‐color infrared signature of the canopy, or large changes in ψΙ, ψΠ, leaf and meristem sugar, K, and amino acid concentrations. The results emphasize the importance of maintaining normal imgation intervals with drip‐irrigated sugarcane cv. H62‐4671.

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