【作者】 张晓；

【导师】 任图生；

【作者基本信息】 中国农业大学 ， 土壤学， 2014， 博士

【摘要】 蒸散由土壤水分蒸发和植物蒸腾组成,研究蒸散中蒸发蒸腾的比例对提高作物的水分利用效率具有重要意义。然而,目前蒸散分解研究中缺乏原位动态测定土壤水分蒸发的方法。近年来,基于感热平衡原理,三针热脉冲传感器被用于测定土壤水分蒸发,但多个三针热脉冲传感器安装的空间位置偏差会对测定结果带来较大误差,且不能得到4mm以上的土壤蒸发部分。本研究的主要目的是通过改进三针热脉冲传感器设计及减小热脉冲技术测量田间土壤热特性的误差,进一步提高感热平衡原理确定土壤水分蒸发的准确性并用于农田蒸散分解的研究中。第一部分描述了改进的多针热脉冲传感器设计及其用于测定土壤水分蒸发的结果。多针热脉冲传感器由7个温度针和4个加热针组成,相当于4个三针热脉冲传感器的组合,并且增加了1和2mm处温度的测量。多针热脉冲传感器能够准确地测定土壤温度动态,包括表层1和2mm的温度变化,能够得到土壤热特性并进一步根据土壤感热平衡原理计算土壤水分蒸发。与三针热脉冲传感器相比,多针热脉冲传感器减小了仪器安装过程带来的误差,将土壤蒸发的不可监测区域由0-4mm缩小至0-1.5mm。第二部分改进了热脉冲技术测定时土壤表层热特性的计算方法。田间土壤表层热特性的测定会受到土壤背景温度日变化的影响,土壤背景温度的增加(降低)会造成热特性的低估(高估)。2012年第258天11：00时,土壤背景温度增加造成6-12mm土层的容积热容量(C)和热导率(λ)分别被低估8%和13%。基于Jury and Bellantuoni (1976)方法,利用热脉冲发射前的土壤背景温度,线性外推得到热脉冲测定过程中土壤背景温度的变化,从而修正了土壤背景温度对热脉冲热特性的影响,但0-6mm土层的热特性在白天某些时间(如258天11：00-15：00)仍无法校准。与de Vries模型计算的热特性相比,校准土壤背景温度影响后的热脉冲热特性在6mm以下土层平均偏差较小,C的平均偏差在0.30MJ m-3℃-1以内,λ的平均偏差在0.22Wm-1℃-1以内。而6mm以上土层的热脉冲热特性仍存在较大误差,这是因为热脉冲技术测量6mm以上土层热特性时受到了土壤-大气界面的影响。利用脉冲无限线性热源-绝热边界条件模型代替脉冲无限线性热源模型来计算土壤热特性能够校准土壤-大气界面的影响,校准后的热脉冲热特性误差明显降低：0-6mm土层C和λ的平均偏差分别由0.46MJ m-3℃-1和0.54Wm-1℃-1降低至0.32MJ m-3℃-1和0.12Wm-1℃-1。第三部分利用感热平衡原理测定土壤水分蒸发,与茎流计和蒸渗仪方法结合对农田蒸散进行了分解。2012年8月1日至9月25日,行间位置的土壤累积蒸发比行内位置的土壤累积蒸发大10mm。因此,有必要考虑农田土壤蒸发的空间变异性。与蒸渗仪蒸散相比,感热平衡法和茎流计茎秆能量平衡法得到的蒸散明显偏高,日蒸散量为蒸渗仪蒸散量的1-1.5倍。感热平衡原理不需要土壤水热耦合运移参数或水力特性便可得到土壤水分蒸发速率和蒸发位置,有助于深入了解近地表蒸发和水汽传输过程,对提高农田水分利用率具有重要的理论意义和应用价值。更多还原

【Abstract】 The individual components of evapotranspiration include soil water evaporation and plant transpiration. Research on the proportion of evaporation and transpiration in evapotranspiration is important in order to increase water use efficiency. However, in the present study of evapotranspiration partitioning, few methods can monitor soil water evaporation in situ and continuously. Based on the sensible heat balance theory, three-needle heat-pulse sensors could be used to measure soil water evaporation, while, the positional deviation of three-needle heat-pulse sensors would cause great error and the evaporation above4-mm depth could not be determined. In view of the above problems, the main objective of this study was:improving the design of three-needle heat-pulse sensor and reducing the error of field soil thermal property measured by heat-pulse technique in order to increase the measurement accuracy of soil water evaporation by sensible heat balace theory and further applied to the evapotranspiration partitioning research.The first part described design of the improved multi-needle heat-pulse sensor and showed its field performance. The multi-needle heat-pulse sensor was constructed by seven temperature needles and four heater needles, equivalent of four three-needle heat-pulse sensors and with two more temperature needles at1and2mm depths. The multi-needle heat-pulse sensor can capture soil temperature dynamic, even at the top1and2mm depths. It can measure the soil thermal property and further determine evaporation rate based on the sensible heat balance theory. Compared with the three-needle heat-pulse sensor, the multi-needle heat-pulse sensor could decrease the errors caused by sensor installation and the undetectable zone was reduced from0-4mm layer to0-1.5mm layer.The second part improved the surface soil thermal property calculations during the heat-pulse measurements. When the heat-pulse technique was used to measure surface soil thermal property in the field, the results would be influenced by the diurnal changes of soil ambient temperature. The heat-pulse thermal properties would be underestimated (overestimated) when the ambient temperature increased (decreased). At11:00when the ambient temperature was increasing on Day258in the year of2012, the volumetric heat capacity (C) and thermal conductivity (λ) in the6-12mm soil layer were underestimatied by8%and13%, respectively. Following Jury and Bellantuoni (1976), the change of ambient temperature during heat-pulse measurements could be extrapolated linearly from the ambient temperature dynamic befor heat-pulse measurement, and used to calibrate the influence of ambient temperature changes. But thermal property couldn’t be calibrated at some daytime (e.g.11:00to15:00on Day258). Compared to thermal properties estimated by the de Vries model, the average deviation of heat-pulse thermal properties below6mm depth were small after calibrating the ambient temperature effect. The average deviation were within0.30MJ m-3℃-1for C and within0.22W m-1℃-1for λ, While, the thermal property errors were larger above6mm depth, because it was also influenced by the soil-air interface. The soil-air interface effect could be calibrated by using the Pulse Infinite Line Source-Adiabatic Boundry Condition (PILS-ABC) modle to calculate thermal properties instead of the Pulse Infinite Line Source (PILS) model. After calibrating by the PILS-ABC model, the average deviation was reduced from0.46to0.32MJ m-3℃-1for C and from0.54to0.12W m-1℃-1for μ in the0-6mm soil layer.The third part examined the field evapotranspiration partitioning using the sensible heat balance theory for soil water evaporation. From Aug.1th to Sep.25th in the year of2012, the cumulative evaporation at interrow location was10mm larger than the cumulative evaporation at within row location. Therfore, the spatial variability of evaporation in the corn field could be considered. Compared with the daily evapotranspiration by lysimeter, the daily evapotranspiration determined by heat-pulse technique and sap flow stem heat balance was obvious larger and most values were between1to1.5times of the lysimeter evapotranspiration.The sensible heat balace theory can determine soil water evaporation rate and location without known the soil water and heat transport parameters and hydraulic properties. It has potential to improve the understanding of evaporation and vapor movement in the shallow subsurface soil and increase the field water use efficiency.更多还原