The optimal tensiometer installation position for scheduling border irrigation in Populus tomentosa plantations

Soil matric potential (SMP) is usually monitored by a tensiometer for managing irrigation in forest plantations, so determining where to install the tensiometer is important for improving irrigation efficiency. However, such work has never been conducted for border irrigation, which is commonly used in the intensive cultivation of forest plantations. In a border irrigated Populus tomentosa plantation on sandy loam soil, we monitored the daily changes of SMP at eighteen different positions in soil wetting volume (WV) [expressed in Px y (x means distance from the trunk in cm, y means soil depth in cm)], transpiration (T), and stem growth rate (GR) in a growing season. The fine root distribution was also investigated in two successive growing seasons. The result of time stability analysis showed that, among the eighteen positions, the annual absolute mean relative difference (RD) and the standard deviation of the RD of SMP at P25 40 were not the lowest, but its root mean square error of the SMP relative deviation reached the lowest in the growing season. The root water uptake at P10 10 had the highest influence on T rate (R2 = 0.220, P