Development of mini-lysimeter system for use in irrigation automation of container-grown crops.

Development of more efficient and sustainable irrigation technology is critical to maintain horticultural production in a water scarce future. Sensor controlled irrigation is an emerging technology that has the potential to increase irrigation efficiency and reduce overwatering by using real-time data on container water status to control the timing and volume of irrigation events. This project presents a novel irrigation control system using lysimetry. We develop small scale lysimeters, referred to as mini-lysimeter, which provide a direct measure of actual evapotranspiration (ET) via a change in mass of containerized crops. As such, mini-lysimeter sensors have the potential to be an effective instrument for automatic irrigation scheduling. This paper presents the mini-lysimeter controlled irrigation system design in detail, including the mini-lysimeter sensors, data logger and control system configuration, and the hardware needed to integrate the control system into existing irrigation infrastructure. A proof of concept study is presented where mini-lysimeter (ML) controlled irrigation is compared to a traditional timer-based irrigation schedule. Results show that the ML controlled irrigation system can produce plants of equal size to traditional irrigation methods while using 26% less water on average. The outcome of this study indicates that the hardware presented here is reliable and robust enough to produce quality plants in a real nursery production setting, and this technology provides a novel approach to improving water efficiency in container nurseries.

Applying Plant Hydraulic Physiology Methods to Investigate Desiccation During Prolonged Cold Storage of Horticultural Trees.

Plant nursery production systems are a multi-billion-dollar, international, and horticultural industry that depends on storing and shipping live plants. The storage environment represents potentially desiccating and even fatal conditions for dormant, bareroot, and deciduous horticulture crops, like orchard trees, forestry trees, ornamental trees, and grapevines. When tree mortality is considered within a plant hydraulic framework, plants experiencing water stress are thought to ultimately die from hydraulic failure or carbon starvation. We hypothesized that the hydraulic framework can be applied to stored crops to determine if hydraulic failure or carbon starvation could be attributed to mortality. We used deciduous trees as model species because they are important horticultural crops and provide a diversity of hydraulic strategies. We selected cultivars from six genera: Acer, Amelanchier, Gleditsia, Gymnocladus, Malus, and Quercus. For each cultivar, we measured stem hydraulic conductance and vulnerability to embolism. On a weekly basis for 14 weeks (March-June), we removed trees of each cultivar from cold storage (1-2°C). Each week and for each cultivar, we measured stem water potential and water content (n = 7) and planted trees to track survival and growth (n = 10). At three times during this period, we also measured non-structural carbohydrates. Our results showed that for four cultivars (Acer, Amelanchier, Malus, and Quercus), the stem water potentials measured in trees removed from storage did not exceed stem P 50, the water potential at which 50% of stem hydraulic conductivity is lost. This suggests that the water transport system remains intact during storage. For two cultivars (Gleditsia and Gymnocladus), the water potential measured on trees out of storage exceeded stem P 50, yet planted trees from all weeks survived and grew. In the 14 weeks, there were no significant changes or directional trends in stem water potential, water content, or NSC for most cultivars, with a few exceptions. Overall, the results show that the trees did not experience detrimental water relations or carbon starvation thresholds. Our results suggest that many young deciduous trees are resilient to conditions caused by prolonged dormancy and validate the current storage methods. This experiment provides an example of how a mechanistically based understanding of physiological responses can inform cold storage regimes in nursery tree production.

Management of Grape Powdery Mildew with an Intelligent Sprayer and Sulfur.

Wine grapes are an important agricultural commodity in the Pacific Northwest, where grape powdery mildew (GPM) is one of the main disease problems. The efficacy of various sulfur concentrations and output volumes from an air blast sprayer retrofitted with the Intelligent Spray System (ISS) were evaluated for the management of GPM. The ISS consists of a LiDAR sensor, Doppler speed sensor, embedded computer, flow controller, and individual pulse-width-modulation solenoid valves at each nozzle. GPM cluster severity ranged from 55 to 75% across all trials in the study when the ISS was used at its default spray rate of 62.5 ml/m3 with micronized sulfur at 6 g/liter, which was significantly higher than all other fungicide treatments but lower than nontreated controls. Similarly, leaf incidence values were highest on nontreated vines, followed by micronized sulfur at 6 g/liter applied at 62.5 ml/m3, with all other fungicide treatments being significantly lower in all trials. Using the ISS at the 62.5 ml/m3 rate and a rotation of locally systemic fungicides resulted in the lowest observed GPM leaf incidence and average cluster severity of 11% in both 2019 and 2020, the lowest cluster severity of all fungicide treatments tested. GPM control with the ISS and micronized sulfur was equivalent to a constant-rate air blast treatment at 6 g/liter when the spray rate of the ISS was increased to 125 ml/m3 or the concentration of sulfur was increased to 24 g/liter. In those cases, the amount of sulfur applied to vines was at or above the minimum label rate from bloom until the end of the season, or the entire season, respectively. This study has shown that sufficient disease control cannot always be expected when pesticides are mixed at the same rate as would be used for a constant-rate sprayer in a variable rate sprayer, especially when contact fungicides such as sulfur are used. With appropriate adjustments, the variable-rate ISS can be a useful tool to reduce pesticide quantities, water needed for mixing, and as a result labor, because fewer trips to refill for a given spray event are needed.

Canopy spray application technology in specialty crops: a slowly evolving landscape.

Many specialty crops are susceptible to insects and diseases, and as such are reliant on regular canopy pesticide applications to achieve quality attributes required for salability. The majority of specialty crop producers continue to use antiquated pesticide application technologies for directed canopy spraying such as the radial air blast sprayer that has been associated with chemical wastage and off-target drift of around 40% and 15% of total applied spray volume, respectively. However, precision sprayers are available that result in remarkable improvements to these parameters. The wide-scale adoption of precision sprayers by specialty crop producers remains low. Reasons for the continued dominance of old technologies include risk averseness of farmers and regulatory bottlenecks. However, as farm labor becomes more expensive, less available, and consumers and regulations favor sustainably produced products, motivations to improve spray application efficiency are increasing. While there are many opportunities and future directions application technology may take, sensor-controlled sprayer technology that applies a proportionate amount of spray will likely be the primary technology of precision sprayers going into the future. © 2020 Society of Chemical Industry.

The Nebulous Ecology of Native Invasions.

In the Anthropocene, alien species are no longer the only category of biological organism establishing and rapidly spreading beyond historical boundaries. We review evidence showing that invasions by native species are a global phenomenon and present case studies from Southern Africa, and elsewhere, that reveal how climate-mediated expansions of native plants into adjacent communities can emulate the functional and structural changes associated with invasions by alien plant species. We conclude that integrating native invasions into ecological practice and theory will improve mechanistic models and better inform policy and adaptive ecological management in the 21st century.

Investigating the impacts of recycled water on long-lived conifers.

Recycled wastewater is a popular alternative water resource. Recycled water typically has higher salinity than potable water and therefore may not be an appropriate water source for landscapes planted with salt-intolerant plant species. Coast redwoods (Sequoia sempervirens) are an important agricultural, horticultural and ecological species assumed to be salt intolerant. However, no studies have analysed how salinity impacts coast redwood growth. To determine salt-related growth limitations, as well as susceptibility to particular salt ions, we divided 102 S. sempervirens 'Aptos Blue' saplings evenly into 17 salinity treatments: a control and four different salts (sodium chloride, calcium chloride, sodium chloride combined with calcium chloride, and sodium sulfate). Each salt type was applied at four different concentrations: 1.0, 3.0, 4.5 and 6.0 dS m(-1). Trees were measured for relative growth, and leaves were analysed for ion accumulation. Results showed that the relative stem diameter growth was inversely proportional to the increase in salinity (electrical conductivity), with R(2) values ranging from 0.72 to 0.82 for different salts. Analysis of variance tests indicated that no particular salt ion significantly affected growth differently than the others (P > 0.1). Pairwise comparisons of the means revealed that moderately saline soils (4-8 dS m(-1)) would decrease the relative height growth by 30-40 %. Leaf tissue analysis showed that all treatment groups accumulated salt ions. This finding suggests reduced growth and leaf burn even at the lowest ion concentrations if salts are not periodically leached from the soil. Regardless of the specific ions in the irrigation water, the results suggest that growth and appearance of coast redwoods will be negatively impacted when recycled water electrical conductivity exceeds >1.0 dS m(-1). This information will prove valuable to many metropolitan areas faced with conserving water while at the same time maintaining healthy verdant landscapes that include coast redwoods and other long-lived conifers.