Technical Report No. 37
CONSUMPTIVE USE OF WATER BY SUGARCANE IN HAWAII
Paul C. Ekern
July 1970
ABSTRACT
Water use by sprinkler irrigated sugarcane under flat-bed culture was measured in four 100 ft2 by 5 ft deep hydraulically weighed lysimeters at the Kunia substation of the Hawaiian Sugar Planters’ Association. Nine-week-old one-eye cane transplants were set into a 5-foot grid in Molokai Low Humic Latosol on 27 October, 1968. Water use approached a 1:1 ratio with a conventional class A pan by late March, 1969 for a 3.5 leaf area index. Average values were 0.25 in/day for the midsummer months. The cane was ratooned on 10 May, 1969 and water use was reduced to a 0.33 fraction of pan evaporation. The cane regrew rapidly and water use was again equivalent to pan evaporation by July, 1969. Neither gypsum resistance blocks nor the neutron probe gave acceptable measurements of water withdrawal from Molokai Low Humic Latosol. Clear day net radiation over the canopy with a mid-day reflectance of 0.21 was: net radiation = (1- reflectance) sunlight -0.15 ly/min. Consumptive use by cane or pan often equaled or exceeded the net radiation, indicating strong positive advection of heat from the surroundings. During the early stages of cane growth, percolate from heavy winter rains contained as great as 225 ppm nitrate, but as the cane matured, the percolate had less than 1 ppm nitrate though the content of other solutes such as chloride, sulfate, and silica remained high.