毛乌素沙地杨树防护林内紫花苜蓿蒸散耗水规律的研究

Evapotranspiration of Medicago sativa L.under poplar shelterbelts in Maowusu Sandy Area

本文利用验证后的Penm an-M on te ith模型,计算了内蒙古毛乌素沙地新疆杨防护林内紫花苜蓿的蒸散耗水,结果表明:(1)通过Penm an-M on te ith模型计算得到的蒸散量与涡度相关法实测值平均相对误差为14.73%(R2=0.84),说明利用Penm an-M on te ith模型计算林草复合模式内牧草蒸散量是可行的;(2)不同生育期内紫花苜蓿蒸散量差别较大,具体表现为:返青-分枝阶段、现蕾-开花阶段蒸散量较小,分别为5.03 mm和44.95 mm;分枝-现蕾、开花-结荚阶段蒸散量较大,分别为71.10 mm和101.74 mm;其中耗水最大的生育期为开花-结荚阶段,占整个生育期总耗水量的45.66%。在空间上表现为:随着距主防护林带距离增加,紫花苜蓿蒸散量逐渐增大,最大蒸散量出现在距离林带约115 m处(约7倍树高),为234.41 mm,之后,受另一侧防护林的影响,蒸散量逐渐减少。整个生育期防护林内紫花苜蓿总蒸散量为222.83 mm,对照地紫花苜蓿蒸散量为269.02 mm,与对照相比,防护林内紫花苜蓿比林外蒸散量降低了17.2%。防护林内和对照紫花苜蓿生物量干重分别为3287.28 kg/hm2和2959.93 kg/hm2,林内比对照增产11.1%。

Based on the validated Penman-Monteith model, the evapotranspiration of Medicago sativa L. , grown in the poplar shelterbelts in Maowusu Sandy area, Inner Mongolia, West China, was calculated. The results were as follows. （1） compared with the observational data of eddy-covariance method, the relative error of Penman-Monteith model was 14.73% （R^2 = 0.84）, which showed that Penman-Monteith model was reliable to estimate evapotranspiration of pasture in the shelterbelts ; （2） evapotranspiration of alfalfa in different phonological periods was variable. Evapotranspirations at survival-branching stage, branching-buddlng stage, buddingflowering stage, and flowering-producing stage were 5.03, 71. 10, 44. 95 and 101. 74 mm, respectively. The maximum of evapotranspiration was found at flowering-producing stage, accounting for 45. 66% of the total amount. The spatial variation of alfalfa evapotranspiration was demonstrated with the pattern of ＂low- high-low＂. The further distance it is away from the shelterbelts, the more water alfalfa consumed. The maximum of evapotranspiration occurred at 115 m distance （about 7 times of the tree height） away from the shelterbelts with the amount of 234.41 mm; later on, evapotranspiration decreased gradually due to the impact of the other shelterbelt. Evapotranspirations of alfalfa in shelter belts and monoculture were 222.83 mm and 269.02 mm, respectively. By contrast with monoculture pasture, evapotranspiration of alfalfa in shelterbelts decreased by 17.2%. The biomass （dry weight） values of alfalfa in shelterbeits and by monoculture were 3287.28 kg/hm^2 and 2959.93 kg/hm^2, respectively, which showed that alfalfa in shelterbelts produced 11. 1% biomass more than that by monoculture.