Research Project: Water and Nutrient Management for Sustainable Production of Small Fruit and Nursery Crops

Location: Horticultural Crops Production and Genetic Improvement Research Unit

2022 Annual Report

Objectives
Irrigation and nutrient management are key factors that impact sustainable and profitable production of high-quality small fruit and nursery crops. The goal of this project is to develop new approaches that integrate water and nutrient management methods with other environmental and cultural constraints to improve the quantity and quality of berry, wine grape, and nursery crops grown in the Pacific Northwest (PNW) while protecting the environment. Objective 1: Determine requirements for high-quality berry crop production through monitoring and management of water, nutrients, and soil. [NP 305, Component 1, Problem Statement 1B] • Subobjective 1A: Adapt and refine remote sensing technology to monitor water and nutrient deficits and determine irrigation and fertilizer needs in berry crops. • Subobjective 1B: Assess the feasibility of using deficit or pulsed-drip irrigation to increase water use efficiency and protect regional water quality in berry crops. • Subobjective 1C: Develop new fertigation and soil management practices to increase production and fruit quality in blueberry. Objective 2: Develop approaches to manage vineyard canopies, soils, and nutrients for improved grape production, plant health, and fruit quality. [NP 305, Component 1, Problem Statement 1B] • Subobjective 2A: Develop an integrated nitrogen (N) management approach encompassing N use in both the vineyard and winery to identify the most effective and efficient manner to manage N inputs to improve wine quality and protect water quality. • Subobjective 2B: Examine how canopy architecture, vine density, and crop load interact to identify the most efficient use of sunlight and soil water resources to improve production efficiency of Pinot noir. • Subobjective 2C: Understand how N management practices influence beneficial arbuscular mycorrhizal fungi (AMF) in grapevines to develop more sustainable methods for farming grapes. • Subobjective 2D: Determine the impact of rootstocks on root development and AMF colonization when challenged by the northern root knot nematode. Objective 3: Evaluate the impact of management practices for water and nutrients on tolerance to abiotic and biotic stress in specialty crops. [NP 305, Component 1, Problem Statement 1C] • Subobjective 3A: Develop new management practices and disease control measures to minimize pathogen damage and losses for woody nursery plants. • Subobjective 3B: Define salinity thresholds for specialty crops so growers can reduce losses of planting stock, mitigate salinity impacts on quality, and broaden the use of more salt tolerant species in systems considered marginal for production of other crops. • Subobjective 3C: Develop and evaluate water and nutrient management practices for specialty crops grown in soilless substrates.

Approach
Experiments will be conducted in the greenhouse and field on small fruit (blueberry, raspberry, strawberry, grapevines) and other specialty crops including nursery crops (Rhododendron, Vaccinium, Basil), and in growth chambers on root pathogens. For Obj. 1 we will develop remote sensing based crop coefficients and water stress indices for irrigation of blueberry and raspberry, and will test the following hypotheses: Deficit irrigation will reduce water use but have no effect on yield or fruit quality when it is applied at early stages of fruit development or after harvest in blueberry or raspberry; Pulsed-drip irrigation will reduce water use and increase yield and production relative to conventional irrigation in blueberry and raspberry; Application of P and B by fertigation will result in greater yield and fruit quality than granular or foliar fertilizers in blueberry; Biostimulants are most effective when applied at low rates and during peaks in root production. For Obj. 2 we will test these hypotheses: Maintaining low N status in the vineyard will enhance wine composition as compared to boosting N supply in the vineyard; Varying N supply to Pinot noir alters berry and wine phenolic composition to a greater extent than P or K; Altering the VSP trellis to increase canopy solar exposure at midday will increase productivity but not alter ripening or fruit quality in Pinot noir; Soil and foliar applied N in vineyards reduces AMF colonization and P uptake; Nitrogen inhibition of AMF colonization in grape roots increases with N dose; Nitrogen is a more potent inhibitor of AMF as vine P increases; Root development and AMF colonization differ among rootstock genotypes when northern root knot nematode is present. We will test the following hypotheses for Obj. 3: Critical temperatures for vegetative growth and zoospore formation of Phytophthora isolates will be similar within a species; fungicide sensitivity of Phytophthora is greatest at the optimal temperature for growth; Root rot induced by flooding is more severe than rot under moisture conditions common in nurseries; Reducing water availability minimizes root damage caused by Phytophthora in rhododendron; Increasing N increases root damage caused by Phytophthora in rhododendron; Crop tolerance to salinity will differ among production systems; Southern highbush blueberry plants have different substrate needs than northern highbush blueberry; Strategies to improve water distribution in substrates will increase growth and production in blueberry. Measurements and techniques used in these studies will include standard approaches to measure plant growth, biomass, and yield, plant water status (pressure chamber, porometer), photosynthesis (gas-exchange), fruit quality (refractometry, titratation, HPLC, sensory perception), root production and mycorrhizal colonization (soil cores, microscopy), soil pH and EC, soil water content (TDR, tensiometers), plant and soil nutrients (CNS analyzer, ICP), and pathogen growth (microbiological media) and root damage (visual ratings). We will also utilize multi-spectral cameras and drones to develop new methods to measure plant water status.

Progress Report
In support of Sub-objective 1A, research was continued to investigate remote imaging techniques to monitor plant growth and water requirements in blueberry and raspberry. Two years of remote images were collected from commercial fields located throughout Washington state using a low-altitude, unmanned aerial system (UAS or drone) equipped with a multispectral and a thermal imaging camera. The images ae being processed and analyzed for normalized difference vegetation index (NDVI) and canopy temperature. The NDVI images are providing clear information on development of the canopy in the fields and for estimating irrigation needs at each site. Thermal images are also useful, particularly for assessing spatial variability in water status of fields. Growers can also use the images to determine whether they are scheduling irrigations properly or need to add more water to the field. In support of Sub-objective 1B, field trials are in progress to evaluate new practices for reducing irrigation water in berry crops, including deficit irrigation and pulsed drip irrigation. Results to date indicate that deficit irrigation during early stages of fruit development or after harvest had minimal effect on yield or fruit quality in blueberry. Pulsed drip irrigation, on the other hand, increased soil water availability relative to conventional irrigation in raspberry and, by the second year, increased total production by 7%, or 1,230 kilograms per hectare (kg/ha). Production followed a similar trend the following year and increased by 1,210 kg/ha with pulsing. A similar trial was initiated in a mature, commercial blueberry field. Within the first year of application, pulsing increased yield by 2,200 kg/ha when irrigation was applied at a fixed rate (grower based) and by 3,290 kg/ha when irrigation was scheduled based on daily estimates of crop water use. Higher production was due primarily to greater berry size. Overall, pulsed drip irrigation appears to be a promising method for improving blueberry and raspberry production on light, well-drained soils. In support of Sub-objective 1C1, field trials were conducted to investigate the value of fertigating with phosphorus (P) and boron (B) fertilizer in highbush blueberry. The trials were completed, and manuscripts of the results were prepared. Results indicate that fertigation and granular applications of P fertilizer increased the concentration of P in soil solution within the root zone, but neither had any effect on yield, berry weight, or berry firmness. Questions remain on whether blueberry requires less P than recommended, or if alternative sources or rates of P fertilizer are needed. Leaf B was significantly affected by the fertilizers and within the first year was sufficient with fertigation or foliar applications, but low in the granular treatments and no different than those with no B. Applying B by fertigation or as a foliar spray appears to be preferable over the use of granular B fertilizers. In support of Sub-objective 1C2, a greenhouse trial was conducted to test the response of highbush blueberry to different rates of humic substances. Six cultivars were chosen for the study, including ‘Duke’, ‘Draper’, ‘Legacy’, ‘Top Shelf’, ‘Cargo’, and ‘Last Call’. Each cultivar was grown in a complete nutrient solution with four rates of organic acids. While dry weight differed among the cultivars, humic substance increased shoot dry weight by an average of 33% and 38% in each cultivar when plants were grown with 250 and 500 mg·L-1 active ingredient (a.i.), respectively, but had no effect on shoot dry weight at a lower rate or on root dry weight at any rate. In support of Sub-objective 2A1, field treatments with varying nitrogen were applied with grower collaborators, and vine growth, nutrient status in leaf blades and petioles, vine water status and gas exchange measurements were completed. Crop yield parameters were measured, and fruit was harvested and delivered to collaborators to make wine and monitor fermentations. Sensory analysis was completed by collaborators. For Sub-objective 2A2, spectral analysis to characterize broad groups of phenolics was completed. In support of Sub-objective 2B, first-year field data were collected for soil moisture profiles, plant growth and yield, and vine water status. We also tested and began using a solar panel device with similarity to the ‘Paso panel’ to measure sunlight interception and showed that this approach distinguished between the main plot canopy width treatments. In addition, numerous measurements of gas exchange were made over the season and these data were compared with other new project sites where we have been trying to estimate how much shaded leaves close stomates compared to leaves in the sun, and how much these shaded leaves may contribute to vine transpiration with little carbon gain. We also collected data on fruit quality metrics including brix, pH, titratable acids, and mineral nutrient levels in musts. In support of Sub-objective 2C1, root samples were collected, cleared, and stained for mycorrhizal colonization assays, and nutrient status of the vines was determined. Work that was planned for Sub-objective 2C2 was discontinued since our results last year showed that young vines grown in the greenhouse did not respond similarly to the field-grown vines to added soil versus foliar nitrogen applications. Therefore, a new line of inquiry and a new method to test how mycorrhizal fungi may influence nitrogen uptake was developed and a preliminary greenhouse experiment was begun to test our methods. This research involved building polyvinyl chloride (PVC) chambers with access holes and the use of different nylon or fiberglass mesh sizes to either allow roots access to nitrogen in the chambers or only mycorrhizal hyphae to gain access to nitrogen. The plants are currently being grown using this new system to see if the mesh and chamber system works as designed. In addition, we began preparing grass residues labeled with heavy nitrogen so that we can trace root and mycorrhizal nitrogen uptake from both inorganic and organic forms when placed in soil. In support of Sub-objective 2D, all the field, root and mycorrhizal data were analyzed, and a portion of the results have been published. A draft manuscript of the remaining results from this work was prepared and is currently being reviewed by co-authors of the project. In support of Sub-objective 3A, research evaluating factors altering horticultural crop root health continued as planned. Collaborative research identifying how temperature alters pathogenicity in the boxwood blight pathogen (Calonectria pseudonaviculata) is complete. Collaborative research continues to evaluate effects of irrigation and plant spacing on spread of the boxwood blight pathogen. Collaborative research also continues to establish how pathogens associated with root rot in nursery plants differ in sensitivity to fungicides and on improving methods for producing reliable inoculum of root rot pathogens. In support of Sub-objectives 3A1 and 3A2, research continued to establish critical temperatures for growth, reproduction, and fungicide sensitivity of pathogens associated with root rot in nursery crops. Trials which identified optimal, minimum, and maximum temperatures for growth and zoospore formation are complete. ARS researchers analyzed data from growth sporulation studies and starting trials to assess temperature effects on fungicide sensitivity. In support of Sub-objective 3A3, research continued to identify how substrate moisture alters the incidence and severity of root rot in nursery crops. Trials which identified whether research techniques used in studying root rot are representative of what occurs under nursery conditions are complete. ARS researchers analyzed data, wrote a manuscript, and published results. In support of Sub-objective 3A4, the researchers completed trials to assess whether irrigation practices that reduce water availability can alter disease, analyzed data, and are currently writing a manuscript. In support of Sub-objective 3B, ARS researchers initiated a trial evaluating effects of salinity on growth and quality of basil grown in different production systems. They collected and analyzed pathological and physiological data and continued collaborative research quantifying fertilizer run-off from nursery crops and use of remote imaging for management of nursery plant nutrition and irrigation. Collaborative research developing techniques to assess drought tolerance mechanisms in nursery crops was initiated. In support of Sub-objective 3C2, a trial was initiated to evaluate the effects of irrigation frequency (pulse length) and number of wetting points (number and distribution of emitters per pot) on growth, mineral nutrition, yield, and fruit quality of highbush blueberry in substrate. A subset of plants from each treatment were harvested destructively at the end of first growing season and analyzed for total shoot dry weight, root development, and nutrients in the leaves and stems. Leachate pH and electrical conductivity were also measured and used to monitor salt accumulation and to make adjustments to the fertilizers. Plants were cropped in year two, and fruit were harvested and analyzed for fruit size, firmness, soluble solids, and titratable acidity. The trial is ongoing and will continue for at least one more year.

Accomplishments
1. Nitrogen fertilization in the vineyard produces unique wines and boosts productivity in Chardonnay. Nitrogen is a key nutrient to manage in both the vineyard and winery because it alters vine productivity and influences wine quality by altering yeast metabolism. Nitrogen is often added in the winery when berry nitrogen is low to ensure successful fermentation, which is assuming that winery nitrogen addition produces the same type of wine as compared to fertilizing the vineyard. ARS researchers in Corvallis, Oregon, and researchers at Oregon State University, tested whether vineyard nitrogen fertilization using either soil or foliar applications would produce similar wines as adding nitrogen in the winery over three growing seasons. Boosting fruit nitrogen by fertilizing the soil produced the most unique wines with greater tropical fruit aromas, while adding nitrogen in the winery did not result in a similar wine, even if fruit nitrogen levels and fermentation rates were similar. The researchers also showed that soil fertilization with nitrogen increased vine growth and yield, but foliar nitrogen did not increase vine productivity. These findings allow grape growers and winemakers to better manage nitrogen inputs in the whole wine production system to produce the desired style of wine and maintain or increase vine productivity.

2. Biochar improves growth and fruit production in blueberry. Blueberry fields are often amended with bark or sawdust prior to planting, but many growers are seeking alternatives because cost of these materials has increased considerably in recent years. One possibility is to use biochar, a carbon-rich material produced by burning wood or other biomass under low oxygen conditions. ARS researchers in Corvallis, Oregon, and collaborators at Oregon State University, determined that amending the soil with biochar nearly doubled blueberry plant growth and fruit production while reducing costs by more than $500 per acre over the usual practice of incorporating sawdust into planting beds. The biochar used in the study was manufactured from mixed conifers during conversion of wood debris to bioenergy at a 30 megawatt power plant. These findings indicate that using biochar as soil amendment is not only cost-effective but a good way to improve soil health and increase early returns in blueberry.

3. Optimizing inoculum production methods for infesting soil with Phytophthora species that cause root rot in nursery plants. Phytophthora root rot causes significant losses in many horticultural crops and research on this pathogen requires consistent and predictable production of viable pathogen inoculum. A common method used to produce inoculum of this pathogen can take six weeks to produce and often results in variability among batches of inoculum that can waste valuable resources and delay research progress. ARS researchers in Corvallis, Oregon, identified inoculum moisture content that reduces inoculum viability and used results to develop a new method that produces more reliable inoculum in a shorter time. This research is important to other researchers because it helps explain variability in soilborne Phytophthora inoculum production and storage and provides a new method for producing inoculum more quickly.

4. Salinity damage depends on the source of the salt in blueberry. Excess salinity is a common problem for production of blueberries in arid and semiarid regions. Options to reduce salinity are available, but information on how it limits the plants is needed. ARS researchers in Corvallis, Oregon, and collaborators at Oregon State University, examined ion-specific effects of different salts on plant growth in blueberry and identified thresholds for salinity damage from sodium chloride and calcium chloride, both of which can be prevalent in soils and irrigation water. They determined that sodium chloride reduced growth more than calcium chloride, while calcium chloride resulted in greater leaf damage due to toxic levels of calcium in the tissue. Results from this research will be useful for developing better salinity management practices for commercial blueberry production.

5. Grapevine rootstocks reduce the establishment of the northern root-knot nematode in new vineyards. Plant-parasitic nematodes, microscopic roundworms, feed on the roots of grapevines and can reduce vine productivity and fruit quality. These pests are difficult to control and new control methods are needed. ARS researchers from Corvallis, Oregon, and researchers from Washington State University, examined whether reducing irrigation water applied to a young vineyard or the use of different rootstocks could reduce the numbers of the root-knot nematode. Modifying irrigation practices did not reduce the number of nematodes in grape roots or soils, but growing rootstocks was an effective way to control this nematode pest. These findings will be used by grape growers to aid in plant selection at planting to minimize the impact of nematodes on vine productivity.

6. Experimental methods for inducing Phytophthora root rot that are representative of nursery conditions. Soil moisture influences how Phytophthora pathogens cause root rot in nurseries. Most research experiments with these pathogens flood the soil of plants in containers with water to ensure that root rot develops. However, the degree of flooding used in experiments does not usually occur in nurseries where plants are either maintained in containers that can drain freely or they may periodically sit in a shallow pool of water if drainage is poor. ARS researchers in Corvallis, Oregon, and researchers at Oregon State University, determined that rhododendron root rot was similar in flooded plants in containers as in plants irrigated to mimic different nursery conditions. These results show that prior research using flooding to induce Phytopthera root rot is representative of the amount of damage caused by this pathogen that can occur under actual nursery conditions.

7. Several Phytophthora species cause rhododendron root rot in nurseries. Rhododendrons are an important component of the ornamental nursery industry, but are prone to Phytophthora root rot, despite decades of research. One Phytophthora species, P. cinnamomi, was previously thought to be the primary pathogen causing rhododendron root rot, and although recent research suggests there are several other Phytophthora species that may cause root rot, little is known of their virulence and risk to the industry. ARS researchers in Corvallis, Oregon, and researchers at Oregon State University, determined that at least three other Phytophthora species isolated from Oregon nursery plants can cause similar disease severity as P. cinnamomi, but not all species are equally virulent. This research provides valuable information for other researchers and industry in developing more effective disease control measures.

8. Cool temperatures can increase severity of boxwood blight. Production of boxwood, the most valuable broadleaf evergreen shrub produced by the U.S. nursery industry, is threatened by boxwood blight pathogen, Calonectria pseudonaviculata. The disease is reportedly more severe when environmental conditions are warm, humid, and rainy, yet there is conflicting evidence on the role of temperature and moisture on pathogen biology and disease spread. ARS researchers in Corvallis, Oregon, and researchers at Oregon State University, determined that Oregon isolates of C. pseudonaviculata can grow faster and cause more severe disease at cooler temperatures than those reported previously. Results are important because they suggest that a lower optimal temperature should be included in the current risk model used by industry to predict pathogen infection and in future boxwood blight resistance assays used by researchers and breeders.

9. Irrigation management in nurseries has little impact on root rot control after the pathogen has infected the plant. Phytophthora root rot causes significant losses in nursery crops, and disease tends to be more severe in heavily irrigated or waterlogged conditions. Altering irrigation may be useful in developing integrated disease management practices, particularly when pathogen populations are low. ARS researchers in Corvallis, Oregon, determined that root rot severity increased when more pathogen was present; however, reducing irrigation did not lessen the amount of root rot. Instead, severe root rot often led to increased soil moisture as the roots became progressively compromised in their ability to take up water. Results are important to growers because they indicate that reducing irrigation after infection has occurred does little to control root rot. Instead, root rot control efforts should focus on preventing initial infections.

Review Publications
Sales, B.K., Bryla, D.R., Trippe, K.M., Scagel, C.F., Strik, B.C., Sullivan, D.M. 2022. Biochar as an alternative soil amendment for establishment of northern highbush blueberry. HortScience. 57(2):277-285. https://doi.org/10.21273/HORTSCI16257-21.
Bryla, D.R., Scagel, C.F., Lukas, S.B., Sullivan, D.M. 2021. Ion-specific limitations of sodium chloride and calcium chloride on growth, nutrient uptake, and mycorrhizal colonization in northern and southern highbush blueberry. Journal of the American Society for Horticultural Science. 146(6):399-410. https://doi.org/10.21273/JASHS05084-21.
Prado-Tarango, D.E., Mata-Gonzalez, R., Hovland, M., Schreiner, R.P. 2021. Assessing commercial and early-seral arbuscular mycorrhizal fungi inoculation to aid in restoring sagebrush steppe shrubs. Rangeland Ecology and Management. 79:87-90. https://doi.org/10.1016/j.rama.2021.08.001.
Mestas, A., Weiland, G.E., Scagel, C.F., Grunwald, N.J., Davis, E.A., Mitchell, J.N., Beck, B.R. 2022. Is disease induced by flooding representative of nursery conditions in rhododendrons infected with P. cinnamomi or P. plurivora? Plant Disease. 106(4):1157-1166. https://doi.org/10.1094/PDIS-06-21-1340-RE.
Weiland, G.E., Ohkura, M., Scagel, C.F., Davis, E.A., Beck, B.R. 2022. Cool temperatures favor growth of Oregon isolates of Calonectria pseudonaviculata and increase severity of boxwood blight on two Buxus cultivars. Plant Disease. https://doi.org/10.1094/PDIS-04-22-0769-RE.
East, K.E., Zasada, I.A., Schreiner, R.P., Moyer, M.M. 2021. Irrigation and rootstocks to manage northern root-knot nematode during wine grape vineyard establishment. Plant Health Progress. 23(1):49-56. https://doi.org/10.1094/PHP-06-21-0097-RS.
Tian, T., Ruppel, M., Osborne, J., Tomasino, E., Schreiner, R.P. 2022. Fertilize or supplement: The impact of nitrogen on vine productivity and wine sensory properties in Chardonnay. American Journal of Enology and Viticulture. 73(3):148-161. https://doi.org/10.5344/ajev.2022.21044.
Weiland, G.E., Scagel, C.F., Grunwald, N.J., Davis, E.A., Beck, B.R., Mitchell, J.N. 2022. Irrigation frequency and volume has little influence on Phytophthora root rot in container-grown rhododendron. Journal of Environmental Horticulture. 40(2):67-78. https://doi.org/10.24266/2573-5586-40.2.67.