Relating Calculated Leaf Area Index, Evapotranspiration, and Irrigation Method of Sugarcane

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Abstract
The determination of the considerable amount of water used in south Florida for crop production has been time‐consuming and expensive. The Standard Class A National Weather Service pan evaporation (SPE) has been used to estimate evapotranspiration (ET), but requires crop coefficients, ET/SPE, which vary with plant development stage, season, leaf area index (LAI), yield, and irrigation method. The objective of this study was to establish relationships among ET, SPE, LAI, yield of plant and two ratoon crops of sugarcane (Saccharum spp.), and two irrigation methods. Lysimeters were used for 3 yr (1980‐1982) on a Boca fine sand (loamy, siliceous, hyperthermic Arenic Ochraqualfs). Irrigation methods were drip irrigation and subirrigation systems. Total crop seasonal ET values were 1322 mm for drip irrigation, and 1275 mm for subirrigation. The sugarcane average yield under drip irrigation (143 t/ha) was significantly higher than that under subirrigation (119 t/ha), and was linearly related to the ET. The crop coefficient is curvilinearly related to the LAI. The relationship of ET/SPE to LAI was: 0.649 + 0.185 LAI − 0.025 LAI2 (R2 = 0.77) for both irrigation methods. The relationship of ET/SPE to LAI of the second ratoon under subirrigation was: 0.599 + 0.089 LAI − 0.011 LAI2 (R2 = 0.87).