Analysis of the factors influencing surface temperature in summer maize field

Chinese. 农田表面温度变化规律及其特征的研究，对于采用该指标进行农田墒情监测具有重要的实践指导意义。以华北平原夏玉米农田尺度为研究对象，采用涡度相关技术和热红外遥感技术，研究了夏玉米全生育期内不同环境条件下农田能量平衡各分量及气温环境因素与农田表面温度的关系。在不存在土壤水分胁迫情况下，夏玉米不同生育阶段日变化过程中，气温与农田表面温度的相关程度不同，叶面积指数(LAI)较低时二者高度相关，随着生长发育LAI的增加，二者相关程度降低且分散程度增大；净辐射和潜热通量的大小是确定农田表面温度高低的主要能量因子，二者相关程度随着生育期LAI的增减呈抛物线变化趋势, 晴天日农田郁闭时，农田表面温度与能量平衡各分量之间的相关程度达到最高。季节变化过程中，日平均表面温度和瞬时表面温度与日平均气温和瞬时气温间呈高度相关。夏玉米生长大喇叭口期至乳熟期，0～100 cm土层土壤相对含水量超过65%以上时，晴天或云天日表面温度与气温差值相差不大，基本稳定，平均为-5.3℃。农田表面温度的高低是由作物生长势和外界的辐射、土壤水分状况等因素共同作用确定。

English. The variation regularity and characteristics of surface temperature in field are important for monitoring soil and crop water status. Energy flux and surface temperature at field scale were differently measured using the eddy covariance technique and remote sensing in summer maize field in the North China Plain, the effect of energy balance components and air temperature on the diurnal and seasonal variation of surface temperature was analyzed during the whole growth and development period of maize. The relationship between surface temperature and air temperature in diurnal pattern was remarkable different for the difference of leaf area index (LAI) under no-water stress. It was a good linear correlation between them at 0.01 level under small LAI, but complex during full cover period. Net radiation and latent heat flux were the main energy factors influencing surface temperature, the variation of correlation degree between them showed a parabola curve with LAI increasing and decreasing, and there was a highest correlation between surface temperature and energy balance components during full cover period under clear day(α=0.01). There was a close correlation between average daily surface temperature and average daily air temperature, transient surface temperature and air temperature in the seasonal pattern. The value of the surface-air temperature difference was about -5.3℃ under clear day when the soil water content was above about 65% of field capacity in depth of 0 cm-100 cm. In conclusion, surface temperature is determined by many factors, such as crop growth potential, radiation and soil water conditions and so on.