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

Location: Horticultural Crops Production and Genetic Improvement Research Unit

2023 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, remote images were collected from commercial fields of blueberry and raspberry and analyzed for normalized difference vegetation index (NDVI) and canopy temperature. The NDVI images provided clear information on plant canopy development and irrigation requirements at each site, while the thermal images were used to assess spatial variability in water status of the fields. Additional images are being collected this year to develop a crop water stress index (CWSI) for blackberry. In support of Sub-objective 1.B.1, a new trial on deficit irrigation was initiated in blackberry. Irrigation was scheduled automatically using a large weighing lysimeter, and treatments included irrigation and no irrigation after harvest. Deficit irrigation reduced water use by 54 percent (%) but had no effect on primocane growth during the first year of treatment. We are currently measuring yield and fruit quality in the plants from each treatment. In support of Sub-objective 1.B.2, field trials evaluating the benefits of pulse drip irrigation were completed in blueberry and raspberry. Both studies were conducted in mature, commercial fields located in Washington state. Soil at the sites were loam and silt loam, respectively. Plants in the blueberry field were managed organically and harvested for the fresh market, while those in the raspberry field were managed conventionally and harvested for the processed market. Within the first year of application, pulsing increased yield in blueberry by 2200 kg·ha-1 when irrigation was applied at a fixed rate (grower based) and by 3290 kg·ha-1 when irrigation was scheduled based on daily estimates of crop evapotranspiration. Pulsing also increased yield by 1230 kg·ha-1 in year 2 and 1210 kg·ha-1 in year 3 when irrigation was applied at a fixed rate in raspberry. Based on current market prices, increases in production with pulsed drip were equivalent to $11,680–21,160/ha in blueberry and $2,420–2,460/ha per year in raspberry. Higher production was due primarily to greater berry size in blueberry and to more and larger floricanes in raspberry. Overall, pulsed drip irrigation appears to be a promising method for improving production of blueberry and raspberry, but more research on the use of this practice on other soil types is needed. Manuscripts on the studies were prepared and submitted for publication. In support of Sub-objective 1.C, we repeated a trial on the response of highbush blueberry to humic substances. Plants were grown in a complete nutrient solution with four rates of humic acids, including 0, 100, 200, and 300 mg·L-1 of active ingredient (a.i.). The results confirmed our previous results and indicated that humic acids increased shoot dry weight by an average of 36% when plants were grown with 200-300 mg·L-1 a.i. A manuscript on the study was prepared for publication, and humic acids were tested in a new field trial on five commonly grown cultivars of blueberry, including ‘Aurora’, ‘Cargo’, ‘Duke’, Draper, and ‘Top Shelf’. In support of Sub-objective 2.A.1, all field experiments and winery addition experiments with varying nitrogen were completed, and the sensory analysis of all wines was also completed. The first manuscript from this trial focusing on Chardonnay was published. The second manuscript on Pinot noir is partially complete and has been sent to collaborators to complete their parts. For Sub-objective 2.A.2, we are still waiting to conduct the detailed high-performance liquid chromatography analysis as our collaborator has been unable to complete her laboratory renovation due to supply chain issues. The fruit remains frozen and will be analyzed this fall and winter. In support of Sub-objective 2.B, the second-year field data were collected for soil moisture profiles, plant growth and yield, and vine nutrient and water status. However, due to a frost event shortly after budbreak, there was so little fruit remaining on vines that we could not apply different crop levels to the vines. We continued to explore a solar panel device (similar to the ‘Paso panel’) to measure sunlight interception and showed that this approach was effective in estimating solar interception by the canopy. We also collected gas exchange measures, vine nutrient and water status measures and yield. Fruit quality metrics including degree Brix, pH, titratable acidity, and mineral nutrient levels in the must were also examined, but we did not make wines this year since one of our three main factors (crop load) could not be applied. This trial is ongoing, and the different crop levels will be applied this year. In support of Sub-objective 2.C.1, all data were analyzed and a manuscript using this data was completed. We also began preparing another manuscript which we hope to complete over the next few months. Work that was planned for Sub-objective 2.C.2 was discontinued as explained previously, and we completed a new greenhouse study using chambers added to potted grapevines where either roots could gain access to nitrogen in the chambers or only mycorrhizal hyphae. Results were promising although the system does not work well with soluble forms of N that leached across chambers irrespective of the mesh size. A new experiment using this chamber system with only organic N sources is being planned. In addition, we grew grass plants for 8 months in the greenhouse that were supplied with heavy nitrogen (N15) and produced a large quantity of N15 labeled residue for future experiments. For Sub-objective 2.C.3, we completed a greenhouse study where we manipulated nitrogen and phosphorus supply using a factorial design and analyzed the plant growth and nutrient uptake data. This experiment showed no interaction between nitrogen and phosphorus levels on arbuscular mycorrhizal fungi (AMF) function, and that AMF do not help vines obtain nitrogen from soil, even though high nitrogen reduced AMF colonization. Our results were not expected, and we are designing a new study to assess if AMF can help vines obtain nitrogen from organic sources of N. We also began new work to examine if potassium (K) applications in vineyards will alter AMF root colonization and planned a greenhouse trial to examine how varying levels of soil K influence AMF and if AMF influence K uptake and how this interacts with other nutrients. In support of Sub-objective 2.D, all research and analysis were completed, and another paper was published. In support of Objective 3.A, research evaluating factors altering horticultural crop root health continued as planned. In addition, we completed collaborative research optimizing detection methods for the boxwood blight pathogen and how temperature influences disease. Continued collaborative research evaluating effects of irrigation and plant spacing on the spread of the boxwood blight pathogen was begun. Continued collaborative research establishing how pathogens associated with root rot in nursery plants differ in sensitivity to fungicides. Continued collaborative research improving methods for producing reliable inoculum of root rot pathogens. In support of Sub-objective 3.A.1, and 3.A.2, research was completed establishing critical temperatures for growth, reproduction, and fungicide sensitivity of pathogens associated with root rot in nursery crops. In support of Sub-objective 3.A.3, research was completed to identify how substrate moisture alters the incidence and severity of root rot in nursery crop and identified whether research techniques used in studying root rot are representative of what occurs under nursery conditions. In support of Sub-objective 3.A.4, we completed trials to assess whether irrigation practices that reduce water availability can alter disease, analyzed data, and currently writing manuscript. In support of Objective 3.B, a trial evaluating effects salinity on growth and quality of basil grown in different production systems was finished. We collected and analyzed pathological and physiological data and began writing a manuscript. We also continued collaborative research quantifying fertilizer run-off from nursery crops and use of remote imaging for management of nursery plant nutrition and irrigation and how heat waves alter fertilizer efficiency. Lastly, we continued collaborative research assessing how stem hydraulics give insight into drought tolerance mechanisms in nursery crops and be used to develop informed irrigation practices. In support of Sub-objective 3.C.2, we continued a trial 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 at the end of second growing season and analyzed for total shoot dry weight, root development, and nutrients in the leaves and stems. Fruit was also harvested and analyzed for size, firmness, soluble solids, and titratable acidity. Yield and total dry weight of the plants were greatest when irrigation was triggered at -2kPa and applied using a new type of multi-outlet drip emitter, which was designed to apply water evenly over the surface of the growing medium and prevent formation of dry spots in the pots. Conversely, root development was greater with two standard emitters/pot when irrigation was triggered at -2 kPa and four standard emitters/pot when irrigation was triggered at -4 kPa. In general, roots were well distributed with four emitters/pot but tended to concentrate between emitters when plants were irrigated with two emitters/pot and concentrate near the soil surface when the plants were irrigated with the multi-outlet emitters. The trial is ongoing and will continue for another year.

Accomplishments
1. Temperature alters biology and fungicide sensitivity of prevalent Phytophthora causing root rot in Rhododendron. Phytophthora root rot causes major losses in nursery crops. There is speculation that increased temperatures from global climate change may increase disease risk from pathogens that thrive under these conditions. ARS researchers in Corvallis, Oregon, conducted a series of experiments to evaluate how temperature affects the biology and control of three soilborne Phytophthora species prevalent in the nursery industry. Our findings help define the temperatures at which these pathogens will be the most damaging and help delineate the temperatures at which fungicides should be applied for maximum efficacy. An important environmental goal for the nursery industry is to reduce environmental impact from chemical treatments; therefore, determining optimal temperatures for fungicide application not only reduces financial costs of production but also decreases environmental impact.

2. Effective mycorrhizal fungi isolates identified among fungi native to vineyard soil. Root symbiotic fungi known as arbuscular mycorrhizal fungi (AMF) are needed for grapevines to grow in soils with limited phosphorus, but grapevines are colonized by numerous species of AMF in the field. An ARS researcher in Corvallis, Oregon, and student at Oregon State University, compared how different native species of AMF promoted growth and nutrient uptake in grapevines. Results showed that two species were superior in promoting vine phosphorus uptake, and one of these also stimulated greater shoot growth than all the other fungi tested. One species did not colonize roots beyond a trace and had no impact on vine performance. Another species promoted greater uptake of manganese than the other fungi. The most effective isolates can be used to create AMF inoculum for specific production needs for vineyards.

3. Fertigation increases potassium in blueberries. Potassium (K), the second most abundant nutrient in plants, is removed in large quantities during harvest, leaf fall, and pruning of perennial fruit crops. ARS researchers in Corvallis, Oregon, investigated different methods of applying K to cultivated blueberries, including fertigation, which is the practice of applying liquid forms of fertilizer through the irrigation water. Work was conducted in a mature blueberry field irrigated by drip. Within one year, fertigation resulted in nearly twice as much K in the soil as the non-fertigated treatments and, as a result, increased K in the shoots and leaves on the plants. Findings from this work indicate that fertigation with K is more effective than applying granular fertilizers and may be useful at sites where leaf and soil K levels are below the recommended range for blueberry.

4. More efficient and sensitive method for detection of the boxwood blight pathogen. Boxwood blight is a serious plant disease affecting the $141 million U.S. boxwood industry. Symptoms of the disease start out as leaf spots and stem lesions and are usually followed by rapid leaf blight and significant defoliation, particularly during wet and warm weather. However, when the weather is dry, the symptoms may be very mild and difficult to detect. As a consequence, a greater number of plants must be screened in order to detect boxwood blight when symptoms are mild. ARS researchers in Corvallis, Oregon, and a researcher at Oregon State University, developed a protocol to extract and amplify the DNA of the boxwood blight pathogen from large amounts of plant tissue. The protocol is specific for the boxwood blight pathogen and is more sensitive than previous methods. This protocol will help detect the pathogen in a large-scale boxwood blight survey being conducted in Oregon nurseries.

5. Inoculating mycorrhizal fungi in vineyards in the Columbia River Basin is not necessary. Grape growers in the arid Columbia River Basin region lack information regarding how to best manage arbuscular mycorrhizal fungi (AMF), including knowing whether or not to inoculate vines when planting or replanting vineyards and what factors may influence AMF in established plantings. ARS researchers in Corvallis, Oregon, and a colleague from Washington State University, examined AMF root colonization, soil and vine nutrient levels, and nematode populations in 32 wine grape vineyards and conducted a seasonal study in a vineyard with high populations of the northern root-knot nematode pest. Results indicated that root colonization by AMF was just as high in one to two year-old vineyards as in much older vineyards. Lower root colonization by AMF was most closely linked to high soil and plant nitrogen levels, and to high levels of the northern root-knot nematode. These findings show that wine grape growers in the region do not need to inoculate vines with AMF when planting or replanting vineyards but should carefully manage nitrogen inputs and control the northern root-knot nematode to ensure healthy and functional AMF in roots.

6. Water footprint of blueberries. A “water footprint,” defined as the amount of water necessary to produce a unit of a particular product, is a means to evaluate utilization of freshwater resources for human activities, including agriculture. In collaboration with faculty at the University of Buenos Aires in Argentina and the University of Concepción in Chile, an ARS researcher in Corvallis, Oregon, determined the water footprint for producing blueberries. Three widely grown cultivars were evaluated, including ‘Star’, ‘Emerald’, and ‘Snowchaser’. The annual footprint of each, which included water utilized from rain, drip irrigation, and sprinklers for frost protection, differed among the cultivars and ranged from 25-69 gallons of water to produce a pound of berries in ‘Star’, 35-118 gallons of water to produce a pound of berries in ‘Emerald’, and 64-487 gallons of water to produce a pound of berries in ‘Snowchaser’. ‘Snowchaser’ bloomed at the beginning of winter and therefore required more water for frost protection than ‘Emerald’ and ‘Star’, while ‘Star’ lost most of its leaves during the winter, flowered late, and consequently used the least amount of water among the cultivars. Irrigation designers can use this information to quantify water requirements for each cultivar and allocate water for irrigation and frost protection accordingly.

7. 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 a researcher at Oregon State University, determined that Oregon isolates of C. pseudonaviculata are capable of growing faster and causing more severe disease at temperatures cooler than those reported previously. Results are important because they suggest that a lower optimal temperature might need to 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.

8. 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 management 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 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 infection in the first place.

9. Experimental methods for inducing Phytophthora root rot 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 container 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 a researcher at Oregon State University, determined that rhododendron root rot was similar in flooded plants in containers and plants irrigated to mimic nursery conditions. These results are important because they ensure that research conditions are representative of the amount of damage that occurs in nurseries.

10. Optimizing fertilizer practices under different irrigation management regimes improves end product quality of Rhododendron nursery plants. Sustainable nursery crop production requires optimization of two major inputs, fertilizer and water, to achieve growers' economic and environmental goals. Achieving these goals requires information on how plants respond to the combined effects of these inputs. ARS researchers in Corvallis, Oregon, and researchers at Mississippi State University, investigated how fertilizer and irrigation management during container production of rhododendron influenced plant growth, flowering, and nutrient uptake after transplanting into the landscape. The results indicate that manipulating fertilizer and irrigation frequency and volume can be used to alter nursery stock qualities and improve subsequent performance in the landscape. Nursery production strategies that improve plant survival, growth, and productivity after transplanting can substantially improve the value of nursery crops.

11. A new model for optimizing irrigation in hazelnuts. Knowing the exact amount of water required by a crop is essential for irrigation planning and for improving the efficiency of irrigation water use. In collaboration with faculty at the University of Concepción in Chile, an ARS researcher in Corvallis, Oregon, developed a new model for estimating the water requirements in hazelnut. The model was evaluated for three growing seasons in orchards irrigated by drip or micro-sprinklers. Results were highly correlated with measurements obtained from nearby weather stations and indicated the model accurately calculated daily and seasonal water use under a variety of growing conditions. This model will be useful for optimizing irrigation in hazelnuts and other perennial cropping systems.

Review Publications
Leon-Chang, D.P., Bryla, D.R., Scagel, C.F. 2023. Response of northern highbush blueberry to fertigation and granular applications of phosphorus fertilizers. Acta Horticulturae. 1357:51-58. https://doi.org/10.17660/ActaHortic.2023.1357.8.
Pannunzio, A., Holzapfel, E., Cirelli, A., Texeria, P., Souto, C., Bryla, D.R. 2023. Agricultural water footprint for southern highbush blueberry produced commercially with drip irrigation and sprinkler frost protection. Agricultural Sciences. 14(1):114-128. https://doi.org/10.4236/as.2023.141008.
Leon-Chang, D.P., Bryla, D.R., Scagel, C.F., Strik, B.C. 2022. Influence of fertigation and granular applications of potassium fertilizer on soil pH and availability of potassium and other nutrients in a mature planting of northern highbush blueberry. HortScience. 57(11):1377-1386. https://doi.org/10.21273/HORTSCI16747-22.
Souto, C., Lagos, O., Holzapfel, E., Ruybal, C., Bryla, D.R., Vidal, G. 2022. Evaluating a surface energy balance model for partially wetted surfaces: Drip and micro-sprinkler systems in hazelnut orchards (Corylus avellana L.). Water. 14(24). Article 4011. https://doi.org/10.3390/w14244011.
Scagel, C.F., Weiland, G.E., Beck, B.R., Mitchell, J.N. 2023. Temperature and fungicide sensitivity in three prevalent Phytophthora species causing Phytophthora root rot in rhododendron. Plant Disease. https://doi.org/10.1094/pdis-11-22-2670-re.
Schreiner, R.P., Tian, T. 2022. Performance of taxonomically diverse native isolates of mycorrhizal fungi in symbiosis with young grapevines. HortScience. 57(9):1135-1144. https://doi.org/10.21273/HORTSCI16648-22.
Bi, G., Scagel, C.F., Bryla, D.R. 2022. Nitrogen rate, irrigation frequency and volume differentially influence growth, flowering, and nutrient uptake of container-grown rhododendron during the following growing season. Horticulturae. 8(7). Article 647. https://doi.org/10.3390/horticulturae8070647.
Ohkura, M., Scagel, C.F., Weiland, G.E. 2023. Rapid and scalable DNA extraction and real-time PCR assay from boxwood tissue for the detection of Calonectria pseudonaviculata, causal agent of boxwood blight. Plant Disease. 107(5):1279-1283. https://doi.org/10.1094/PDIS-06-22-1453-SR.
Mestas, A., Weiland, G.E., Scagel, C.F., Davis, E.A., Mitchell, J.N., Beck, B.R. 2023. Greater rate of nitrogen fertilizer application increases root rot caused by Phytophthora cinnamomi and P. plurivora in container-grown rhododendron. Plant Pathology. https://doi.org/10.1111/ppa.13776.
Schreiner, R.P., Moyer, M.M., East, K.E., Zasada, I.A. 2023. Managing arbuscular mycorrhizal fungi in arid Columbia Basin vineyards of the Pacific Northwest United States. American Journal of Enology and Viticulture. 74(1). Article 074002. https://doi.org/10.5344/ajev.2023.23005.