Effect of a soil water balance controlled irrigation on the cultivation of Acer pseudoplatanus forest tree liners under non-limiting and limiting soil water conditions

Over the past years, we experienced more extreme weather conditions during the growing season, April till October, with prolonged droughts. Rain-fed production of high-quality forest trees was possible, but recent droughts proved to have an economic impact on the plant quality. Therefore, the hardy nursery sector demands irrigation thresholds and suitable tools including soil and plant sensors to schedule irrigation based on crop water demand. Two trials were conducted with Acer pseudoplatanus liners (1 + 0) grown in a sandy soil in 2022 and 2023 at Viaverda (Destelbergen, Belgium). A rain-fed treatment was compared with a sprinkler irrigation treatment in both trials. Irrigation doses were evaluated with a soil water balance model, which is based on reference crop evapotranspiration (ET0), rainfall, and soil hydraulic properties. The soil water balance model was calibrated based on the measurements of soil sensors and soil samples. Simultaneously, stem water potential at solar noon, tree length, and growth were measured. The irrigation treatment had a positive effect on the stem water potential of Acer in both trials with a less negative value, ±0.7 MPa, compared to the rain-fed treatment. Irrigation increased growth with 28.4% in 2022 and 5.8% in 2023 compared to the rain-fed treatment, resulting in trees of higher commercial quality that could even be classified into a superior grading range in 2022.