Characteristics of spring maize sap flow and its environmental influencing factors in typical mollisol area

Clarifying the variations of sap flow rate of spring maize in the typical mollisol area and its main control factors is of great significance to explore water consumption from transpiration and regulate field water management. In this study, we installed the wrapped sap flow sensors and TDR probes to continuously monitor the sap flow rate of spring maize during filling-maturity stage and soil water and heat conditions of topsoil. In combination with meteorological data collecting from a nearby automatic weather station, we analyzed the correlation between the sap flow rate of spring maize and environmental factors at different time scales. The results showed that the sap flow rate of spring maize in typical mollisol area had an obvious fluctuation of high diurnal and low nighttime. The instantaneous sap flow rate peaked at daytime, with a value of 139.9 g·h^-1, but being weak at nighttime. The starting time, closing time, and peak values of spring maize sap flow were significantly inhibited in cloudy and rainy days, compared with that in sunny days. On hourly scale, the sap flow rate was significantly correlated to solar radiation, saturated vapor pressure deficit (VPD), relative humidity, air temperature, and wind speed. On daily scale, only solar radiation, VPD, and relative humidity were significantly correlated with sap flow rate, with the absolute values of correlation coefficient being all above 0.7. Due to high soil water content during the observation period, the sap flow rate was not significantly correlated with soil water content and soil temperature of 0-20 cm layer, with the absolute values of correlation coefficient being less than 0.1. Under the condition without water stress, solar radiation, VPD, and relative humidity were the top three influencing factors of sap flow rate in this region, on both hourly scale and daily scale.