玉米农田行尺度土壤热特性变异特征及其对土壤含水量和温度的响应

农田土壤热特性受地表能量平衡、土壤特性和作物生长的影响，存在显著的时空变异性，而目前缺乏关于作物行尺度土壤热特性变异特征的研究。本研究采用定位试验，利用热脉冲技术监测了玉米农田行尺度四个位置处（1/2行间、1/4行间、棵下和棵间）两个深度（2 cm和4.5 cm）土壤热特性的时空变异规律，并分析了土壤温度和含水量对土壤热特性的影响。结果表明，在试验期间，热导率、热容量和热扩散率的变化范围分别为0.66—2.22 W/(m?K)，1.46—4.49 MJ/(m3?K)和4.07×10-7—6.88×10-7 m2/s。降雨之后，热导率和热容量增加，且随着时间推移逐渐降低。2 cm深度的土壤热特性的波动较大，棵下位置土壤热导率和热容量值最大，波动最为明显；土壤热扩散率在1/2行间位置最大。在4.5 cm深度，各位置土壤热特性变化趋势基本一致，土壤热导率和热容量值在1/2行间位置最大，土壤热扩散率在棵间位置最大。综合两个土层数据得出1/4行间位置的热导率和热容量更具代表性。本研究中土壤热特性对土壤含水量的响应规律较为明显，随着土壤含水量增加，热导率和热容量线性增加，热扩散率则表现出先增加后降低的规律。在测定的土壤温度范围内，热扩散率随土壤温度增加呈上升趋势。该研究可以为农田水热管理提供理论依据。

WANG Yueyue1, REN Tusheng2*

Soil thermal properties are the key parameters for studying various soil physical processes, which can affect the soil energy balance and mass exchange on the surface of farmland. Even in the same field, there are great differences in soil physical, chemical and biological properties in different position, resulting in a certain temporal and spatial variability in soil thermal properties. The soil water and heat characteristics have been explored in regional and field scale, while there is currently a lack of research on the temporal and spatial variation of soil thermal properties at row scale. The objectives of this study are to explore spatial and temporal variability of soil thermal properties in row scale, and to determine the relationship between soil thermal properties and soil temperature, soil water content in maize field. The experiment was conducted in a maize field, on the 39th day after maize planted, soil thermal properties and soil water content were measured in situ at four positions (under the maize plant (U), interrow with one-fourth row spacing (1/4 R), in the middle of interrow (1/2 R), in the row between two maize plants (1/2 IR)) and two depths (2 cm and 4.5 cm) using multi-needle heat-pulse probes and time domain reflectometry (TDR) technique. The results showed that soil thermal conductivity, heat capacity and thermal diffusivity ranged from 0.66 to 2.22 W/(m?K), 1.46 to 4.49 MJ/(m3?K) and 4.07×10-7 to 6.88×10-7 m2/s, respectively. After rainfall, soil thermal conductivity and heat capacity were increased rapidly, then decreased gradually. The fluctuation of soil thermal characteristics was large at the depth of 2 cm soil depth, especially at the position under the maize plant. At 2 cm soil depth, the values of soil thermal conductivity and heat capacity were the largest at the position under the maize plant, while the soil thermal diffusivity at the position in the middle of interrow was the largest. At 4.5 cm soil depth, the change trend of soil thermal characteristics at each position was basically the same. Soil thermal conductivity and heat capacity at 1/2 R were the largest, and the soil thermal diffusivity was the largest at 1/2 IR. Combined the soil thermal characteristics data of two depths, the thermal conductivity and heat capacity were more representative at the location of 1/4R. In this study, soil water content was the key factor affecting soil thermal conductivity and heat capacity. We found that soil thermal conductivity and heat capacity increased with the increase of soil water content, while soil thermal diffusivity increased at first (when soil water content lower than 0.15 cm3/cm3) then decreased. In the range of soil background temperature measured during the experiment period, no obvious relationship between soil thermal conductivity and soil background temperature was discovered, soil volumetric heat capacity decreased slightly with increasing temperature at 4.5 cm soil depth, while the soil thermal diffusivity increased with the increase of soil temperature. Therefore, the temporal and spatial variability of soil thermal properties should be considered when monitored at row scale in field. The results can provide an important theoretical basis for farmland hydrothermal management.