Search Results

Controlled-release fertilizers (CRFs) are water-soluble pellets of homo- or heterogenous mineral nutrients covered with polymer or resin that become increasingly porous as temperature increases, releasing water-soluble fertilizer through diffusion. An experiment was carried out at the North Willamette Research and Extension Center located in Aurora, OR, USA (lat. 45°16′51″N, long. 122°45′04″W) with six fertilizer concentrations of a CRF fertilizer that was designed to last 6 to 7 months at 70 °F. During the experiment, the Pacific Northwest experienced a series of early-summer (June) heatwaves that caused an unanticipated and excessive release of mineral salts. Extreme weather adaptation strategies are necessary to sustain horticultural production in a period with increased temperature volatility.

This study reviews how mini-lysimeters have been used effectively to optimize irrigation control in container horticulture production. Lysimeters are devices that measure evapotranspiration (ET) from the water balance of a fixed soil volume. The primary components of lysimeter-controlled irrigation are load cell sensors, a multiplexer, a data logger, a controller, and solenoid valves. The two common mini-lysimeter systems are platform lysimeters and suspension lysimeters. In these systems, a bending-beam single-point load cell is fastened between two plates, and a container is placed directly on the top platform. Platform lysimeters are commonly used for smaller pot sizes, and suspension lysimeters have been used for large shade trees up to 2.8 m tall and weighing 225 kg. Mini-lysimeters have been used for decades to calibrate ET models and create on-demand irrigation control programs that replenish plant daily water use or maintain deficit conditions. Research has demonstrated that lysimeter-based irrigation can respond more effectively to seasonal and diurnal variations in water demand, increasing irrigation cycles when evaporative demand is high, and decreasing irrigation cycles when demand is low. A strength of these systems is that for containerized plants, such as nursery production systems, mini-lysimeters capture whole-plant water use, which presents a more holistic measure compared with soil moisture sensors or leaf moisture sensors.

The plant nursery industry in Oregon faces increasing challenges from climate change, particularly concerning the cultivation of shade trees grown in nursery production. Shade trees are multimillion-dollar agricultural commodity in Oregon, the number one producer of shade trees in the United States. Oak, maple, and sycamore are common examples of shade trees. Our hypothesis posited that despite being commonly cultivated together in shade-tree production blocks under similar management protocols, these trees employ distinct hydraulic strategies during growth. The aim of this research was to investigate the physiological response of Sunset Red Maple (Acer rubrum ‘Franksred’) and Red Oak (Quercus rubra) to variations in soil moisture and vapor pressure deficit (VPD). The research was carried out at the experimental field-grown nursery located at the North Willamette Research and Extension Center in Aurora, OR, USA. Stomatal conductance (g _s) and stem water potential (ψ_s) were measured to assess plant responses to soil moisture and VPD. When soil moisture was abundant, average Red Oak g _s was 0.26 ± 0.13 mmol·m⁻²·s⁻¹, twice as great as Red Maple, at 0.12 ± 0.09 mmol·m⁻²·s⁻¹. Red Oak g _s was 2.67 times greater than Red Maple g _s under soil moisture deficit. Similarly, at any given soil moisture content Red Oak ψ_s was significantly less negative (−6.22 ± 2.70 bars, n = 384) compared with Red Maple (−12.15 ± 4.45 bars, n = 384). In general, our results revealed distinct responses between the two species, with Red Maple exhibiting greater sensitivity to soil moisture and VPD compared with Red Oak. Furthermore, we observed an important correlation between VPD and maple g _s, with g _s, decreasing in response to increasing VPD whether soil moisture was abundant (R ² = 0.64) or lacking (R ² = 0.69), highlighting the importance of considering atmospheric moisture dynamics in plant water management strategies. These findings underscore the complexity of plant responses to drought and emphasize the necessity of informed water management practices for sustainable nursery production. This research contributes to our understanding of plant hydraulic physiology and provides valuable insights for sustainable nursery management practices, particularly in the face of climate change–induced droughts.