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 < 0.01) and GR (R2 = 0.112, P < 0.05). The fine roots distribution changed greatly with the stand development, but its pattern within the WV was relatively consistent in different years. There were three dense fine roots zones located around P10 10, P40 10, and P10 50. Consequently, it was suggested to place tensiometers at two positions, i.e., P25 40 and P10 10, with the former being used for estimating irrigation amount and the latter for triggering irrigation. This recommended tensiometer placement strategy will not only help to improve the irrigation efficiency in P. tomentosa plantation but also provide a reference for the irrigation management in stands of other tree species.

Automated summary

Monitoring soil matric potential and root distribution in a border irrigated Populus tomentosa plantation can help optimize irrigation management strategies, leading to improved irrigation efficiency.