Effects of drip irrigation and nitrogen fertigation on stand growth and biomass allocation in young triploid Populus tomentosa plantations

Abstract

A field experiment was conducted in 2017–2018 to investigate the effects of drip irrigation and N fertigation (DIF) on stand growth and biomass allocation in a triploid Populus tomentosa plantation in the North China Plain. The experiment, which included a 3 × 4 factorial structure (four levels of additional N fertigation in each of three levels of irrigation) and an untreated control, was laid out as a complete randomized block design with 5 replicates. Based on the proper model for the augmented factorial design, the results of ANOVA for stand basal area increment and stand total biomass in 2017 and 2018 showed that high irrigation (irrigation when soil water potential at soil 20 cm depth reached −20 kPa) significantly enhanced early stand growth, but additional N fertigation did not further improve early stand growth. The Dirichlet regression model was directly fitted biomass proportion data from destructively sampled trees to differentiate between developmental and treatment effects on biomass allocation. After correction for the tree-size effect, the high irrigation or the high-fertigation associated DIF regimes altered biomass allocation to some extent. Additional N fertigation did not affect early stand growth but affected biomass allocation, suggesting the monitoring of longer-term responses is necessary.