HIGH PRECISION WEIGHING LYSIMETERS FOR EVAPOTRANSPIRATION MEASUREMENTS OF SUGARCANE PRE-SPROUTED PLANTLETS

Abstract Sugarcane pre-sprouted plantlets (PSP) production system is an innovative method to enhance crop multiplication rate. Determination of crop evapotranspiration (ETc) is crucial for water requirement identification throughout the plant cycle for irrigation management. ETc can be satisfactorily measured by weighing lysimeters. The objective of the study was to construct and calibrate three low-cost weighing lysimeters to measure ETc of PSP. The built lysimeters had 0.6909 m2 area (1179 mm × 586 mm), with 400 mm depth supported by 3 load cells. Lysimeters calibration showed excellent precision measurements, due to high linear correlation (R2 = 1.0000) between electric signal and equivalent mass, high accuracy, confirmed by mean absolute error between 0.0272 and 0.0382 mm, mean square error between 0.0011 and 0.0024 mm2 and Willmott's index of agreement (d) equal to unit. Maximum hysteresis (0.1951 mm) and hysteresis at full scale (0.4492%) did not compromise the evaluations. Daily ETc measurements showed variation of 0.27 mm among lysimeters and were coincident with daily course of reference evapotranspiration (ETo). The cost of the equipment was low, except for the data acquisition system. Therefore, lysimeters presented low cost and were adequate to measure ETc of PSP in greenhouse-grown.

摘要 甘蔗预发芽幼苗（PSP）生产体系是提升作物繁殖速率的创新方法。精准测定作物蒸发蒸腾量（ETc），是识别作物全生育期需水量、开展灌溉管理的关键环节。称重式蒸渗仪可较为精准地测量ETc。本研究旨在构建并校准三台低成本称重式蒸渗仪，以测量PSP的ETc。所搭建的蒸渗仪面积为0.6909 m²（规格为1179 mm × 586 mm），深度400 mm，搭载3个称重传感器。蒸渗仪校准结果显示其测量精度优异：电信号与等效质量间呈极强线性相关（决定系数R²=1.0000）；平均绝对误差介于0.0272~0.0382 mm之间、均方误差介于0.0011~0.0024 mm²之间，验证了其高精度特性；威尔莫特一致性指数（d）为1，进一步证实了校准效果。最大滞后误差为0.1951 mm，满量程滞后率为0.4492%，均未对测量评估造成负面影响。每日ETc测量结果在三台蒸渗仪间的差值为0.27 mm，且与参考作物蒸发蒸腾量（ETo）的日变化趋势一致。除数据采集系统外，整套设备的购置成本较低。综上，该蒸渗仪成本低廉，适用于温室栽培条件下PSP的ETc测量。