Comparisons Measured Evapotranspiration of Sugarcane from Large a N D Small Lysimeters

Evapotranspiration (E,) was estimated for plant, first ratoon and second ratoon crops in a sugarcane field by means of the water balance in a large plastic-lined lysimeter (405 m2) and three small weighed lysimeters (each 3,71 m2). For the first 230 days of the plant crop of the experiment the mean daily estimates of E , from the large and small lysimeters were 4,14 mm and 4,16 mm respectively. This good agreement was not maintained during the final 80 days of the experiment, when the sugarcane in the large lysimeter was lodged. The consumptive use of water by the crop immediately after lodging was apparently reduced to an extent which could be of practical significance in commercial production. The plant crop results were confirmed by the first and second ratoon data, although the agreement between large and small lysimeters deteriorated progressively. The productivity per unit of water (tons cane per hectare per 100 mm of E,) remained fairly constant throughout the experiment, but, if Class A pan evaporation is taken as a guide to the yield potential in different crops, then it appears that the yield of sugarcane declined in successive ratoons.