基于单作物系数法的温室秋季生菜蒸散量估算及验证

Estimation and verification of autumn lettuce evapotranspiration in greenhouse based on single crop coefficient method

【目的】基于单作物系数法估算温室秋季生菜蒸散量。【方法】通过2021—2022年温室秋季生菜试验,根据各生育期影响因素修正FAO-56推荐作物系数值,即生育前期根据ET0值和灌溉频率修正,生育中期和生育后期根据气象因素和株高修正,并采用单作物系数法对温室生菜蒸散量进行估算,以称重式蒸渗仪实测蒸散量ETcm为标准值对蒸散量估算值ETcs进行验证。【结果】不同试验年度逐日ET0均呈逐渐降低变化趋势,介于1.18~2.44 mm/d。温室生菜作物系数修正值(Kc adj)和实测值(K_(c loc))均在生育前期最高,2 a均值分别为0.74±0.13和0.76±0.13;进入快速发育期后二者均呈降低趋势,并在生育中后期逐渐稳定在0.5~0.6。各生育阶段的Kc adj较FAO推荐值(Kc FAO)更接近实测值(K_(c loc)),Kc adj和K_(c loc)相对误差介于-6.7%~5.4%。应用修正单作物系数法估算温室秋季生菜ETcs与实测ETcm的日均值分别为1.310 mm/d和1.283 mm/d,决定系数(R^(2))、平均绝对误差(MAE)、均方根误差(RMSE)、一致性指数(d)分别为0.975、0.176 mm/d、0.222 mm/d、0.955。【结论】修正单作物系数法能够较为准确的估算温室秋季生菜蒸散量。

【Objective】The variation in evapotranspiration is an important parameter in irrigation design.In this paper,we propose and verify a modified single crop coefficient method to calculate the evapotranspiration of greenhouse lettuce.【Method】The experiment was conducted in autumn from 2021 to 2022 in a greenhouse grown with lettuce.The crop coefficient was calculated using the formula recommended by FAO-56,with the calculated crop coefficient for initial growth stage being modified based on ET_(0) and irrigation frequency,while for other growing stages it was modified based on meteorological factors and plant height.The modified single crop coefficient was then used to calculate the evapotranspiration of the lettuce,with the calculated results being validated against measured data from weighing lysimeters.【Result】The mean reference crop evapotranspiration(ET_(0))of the lettuce varied between 1.18 to 2.44 mm/d,but showed a decreasing trend from 2021 to 2022.The modified crop coefficient and measured crop coefficient both peaked at the initial stage,with their associated two-year average being 0.74±0.13 and 0.76±0.13,respectively.As the crop grew,both crop coefficients asymptotically decreased to 0.5~0.6 in the middle and later growing stages.The modified crop coefficient was closer to the measured crop coefficient than that calculated from the formula recommended by the FAO-56,with the relative error between them ranging from-6.7%to 5.4%.The mean estimated and the measured evapotranspiration of the lettuce in autumn were 1.310 mm/d and 1.283 mm/d,respectively.The determination coefficient,the mean absolute error,root mean square error and the index of the agreement between the measured and estimated evapotranspiration were 0.975,0.176 mm/d,0.222 mm/d and 0.955,respectively.【Conclusion】The modified single crop coefficient is more accurate than that calculated from the formula recommended by the FAO-56 for estimating the evapotranspiration of greenhouse lettuce.