ASHS 2024 Conference

Evaluating Nitrogen Application Rates on Open-field Fresh-market Tomato Production in North Mississippi: Preliminary Results - Ibukun Ayankojo
Effect of Bacterial Biostimulant Applied at Different N Rates in Potatoes - Lakesh Sharma
Evidence of Downregulation in Atmospheric Nitrogen-Fixation Associated with Native Hawaiian Sugarcane - Noa Lincoln
Nitrate Leaching Potential of UAN and Organic Soybean Extract Fertilizers Applied to Lettuce - Dave Goorahoo
Evaluating the N Status of Tomato Supplied with Soluble and Controlled-release Urea Formulations - Laura Jalpa
Understanding Nitrogen Uptake Potential of Two Wetland Plants Under Varied Water Temperatures and Nitrogen Concentrations - Saroj Burlakoti
Understanding the Boron-Yield Relationship in Pistachio Orchards - Mukesh Mehata

Nitrogen (N) is an essential crop nutrient and is a major production requirement for vegetable crops, critical for optimum yield and fruit quality. An adequate supply of N improves plant growth and health, reduces plant susceptibility to diseases, and minimizes the risk of groundwater and surface water pollution. There is limited information on the N requirements for commercial vegetable production systems in Mississippi (MS). This project aims to establish the critical N application rate for open-field fresh-market tomato production in northeast Mississippi. The study was conducted at North Mississippi Research and Extension Center, Verona MS. The evaluated treatments (0, 73, 109, 145, 218, and 290 kg/ha-N) were arranged in a randomized complete block design with three replicates per treatment. For each treatment, the total required amount of nitrogen application was applied at a split rate of 50% preplant (ammonium nitrate, 33-0-0 and fertigation (Calcium nitrate, 15.5-0-0). Fertigation was applied weekly starting at 6 weeks after transplanting. Both potassium and phosphorus were the same for all treatments and applied at 100% pre-plant using 0-46-0 and 0-0-60 formulations respectively. Yield data were collected at fruit maturity and analyzed for statistical differences among treatments. Preliminary results suggest significant differences (p < 0.05) among treatments for leaf tissue N concentration. The total marketable yield and extra-large fruit categories were highest (p < 0.05) at 290 kg/ha-N compared to other treatments. The results also clearly demonstrated that the observed yield increase at a higher N rate (290 kg/ha-N) was attributed to increase in total fruit number at maturity and bigger fruit size. The observed yield for the unmarketable fruit category was highest at N application rate of ≤ 73 kg/ha. Based on the preliminary results obtained, the optimum N application rate for open-field fresh-market tomato production in northeast MS could be up to 290 kg/ha. However, more studies are currently being conducted to validate these preliminary results.

Nitrogen is a crucial macronutrient for potato production, as it plays a vital role in promoting photosynthesis, chlorophyll synthesis, and overall plant growth, ultimately contributing to higher crop yield. However, the shallow root system of potato plants and the sandy soil conditions in this region make applied nitrogen unavailable to the crop, resulting in reduced nitrogen use efficiency (NUE). An alternative and eco-friendly solution is to integrate microbial consortium inoculation in nutrient management plans. This approach entails the introduction of a mixture of beneficial microorganisms known as plant growth promoting rhizobacteria (PGPR), into the soil to promote plant growth. These N2-fixing microbes can increase soil N availability which could meet N demand of potato crop, hence can help in reducing N fertilizer input rate. Therefore, a commercial microbial biostimulant was applied with five different N rates 0, 78, 157, 235, and 314 kg ha-1. We found that microbial biostimulant did not increase tuber yield but improved NUE. Increasing N rate increased tuber yield, biomass and NUE significantly.

The study of nitrogen fixation in sugarcane has a long history that has demonstrated high potential but with substantial variation in results. This 32-month study sought to assess the response of nitrogen fixation associated with sugarcane (Saccharum officinarum L. cvs. ‘Akoki, Honua’ula, and ‘Ula) to available soil nitrogen. Plants were grown in large pots of perlite along with a fixing and a non-fixing plant control and administered liquid fertigation with varying amounts of isotopically enriched nitrogen. Assessment of nitrogen fixation utilized nitrogen isotope tracing and acetylene reduction assay in the target and control plants. Isotope enrichment and acetylene reduction assay both indicated that nitrogen fixation peaked under low nitrogen application, and declined with higher application rates, with agreement between the two methods. These results suggest that sugarcane engages in a downregulation of nitrogen fixation under high nitrogen availability, potentially explaining the high variation in published experimental results. This suggests that nitrogen management and fertilization strategy can impact the atmospheric inputs of nitrogen in sugarcane cultivation, and the potential to improve nitrogen application efficiency in cropping systems utilizing sugarcane.

In California, lettuce (Lactuca sativa) production generates over $1.8 billion in revenue. As a leafy green vegetable, Nitrogen (N) fertilizer applications can reach as much as 280 kg N/ha. The relative shallow root systems and frequent irrigation can enhance Nitrate (NO3) Leaching Potential (NLP) when the crop is grown on Sandy Loam soil. Because of economic, health, and environmental concerns, growers are exploring the option of using organically approved fertilizers such as water-soluble N derived from soy protein hydrolysate (GS) as an alternative to Urea Ammonium Nitrate (UAN). The objective of this study was to compare the NLP of equivalent rates of UAN and GS applied to a (1) soil-column study (Phase 1) and (2) greenhouse lettuce crop with 3 Irrigation regimes x 2 Fertilizers x 4 Rates as a factorial experiment replicated four times (Phase 2). In the Phase 1 study, approximately 2,150 ml of water containing a chloride (Cl) tracer and fertilizers at rates of 0, 56, 112, and 168 kg N/ ha were applied to a fixed volume of soil at a bulk density of 1.35 g/cm3. The chloride concentrations in the leachate from both fertilizer treatments were similar, and the water balance accounted for 95% of the solution applied. The concentration and amount of NO3 in the leachate collected from soil treated with GS were lower or at least equal to that obtained from the soils treated with UAN. In contrast, the amount of residual soil NO3 was significantly higher in the soil receiving the UAN, ranging from 2 to 4 times as the application rates increased from 56 to 168 kg N/ha, respectively, implying a relatively higher NLP for the UAN. In the case of the lettuce experiment (Phase 2), there were no significant differences in the chlorophyll content based on the choice of fertilizer or application rates. Lettuce yields, expressed on a dry matter basis, were not significantly (p=0.11) different for fertilizer type, with similar fertilizer rate response curves being obtained for both UAN and GS. Finally, the mean %N and %C in the lettuce leaves were 3.22% and 40%, respectively, regardless of whether the lettuce was grown with synthetic UAN or organically derived soybean hydrolysate (GS). These preliminary findings justify the need to investigate further the impact of higher irrigation rates and even saturated conditions on the NLP of vegetables subjected to the two fertilizers used in the current study.

Matching crop nitrogen (N) demand and supply is necessary to increase crop N use efficiency (NUE) and reduce environmental impact. Proximal optical sensors such as the Soil Plant Analysis Development (SPAD) meter have been found to be useful in monitoring the crop N status, providing insight into the effects of N fertilization practices in cropping systems. High N rate applications are common in conventional tomato production, where loss of N, more specifically NO 3 - , from the rootzone can decrease water quality. Thus, optimal N management of fertigated vegetable crops requires frequent and rapid assessment of the crop N status to quickly adjust application of N when required. A two-year field study was conducted in north Florida to evaluate the crop N status based on N fertilization practices associated with soluble urea and polymer coated controlled-release urea (CRU) for fall and spring tomato (‘HM 1823’) grown in sandy soils under a plastic-mulched bed system. In addition to a no N fertilizer treatment, three urea N sources [one soluble source and two polymer-coated CRU sources with different N release durations of 60 (CRU-60) and 75 (CRU-75) days] were applied at three N rates (140, 168, and 224 kg ha -1 ), where 224 kg ha -1 is the recommended N rate for tomato production in Florida. Soluble urea was split applied weekly over the 13-week growing season, whereas CRUs were applied at the full rate once at preplant. For all seasons, biweekly SPAD meter readings were taken and sampling periods coincided with the vegetative, flowering, fruit set, fruit growth, and harvest growth stages. Overall, minimal differences in tomato N status were observed among the tested N rates and N sources, indicating that all N fertilizer practices tested maintained similar N use. Thus, irrespective of the N source, this study found that tomato N demands could be met at a 38% reduction of the recommended N rate, potentially enhancing NUE in tomato production systems cultivated on sandy soils in north Florida.

Excessive use of commercial fertilizers in nursery production results in substantial fertilizer runoff, leading to surface and groundwater contamination. Therefore, to prevent contamination and comply with regulations, irrigation return flow (runoff water) is generally collected in a retention pond before it can be safely discarded or released. Nitrogen, applied as nitrate compounds is among the highest used fertilizer and is prone to leaching and runoff. Employing a phytoremediation strategy to remediate irrigation return flow (runoff water) has the potential to lower nitrate concentrations in water before release. In this study, we assessed the suitability of growing Helianthus maximiliani (maximilian sunflower) and Asclepias speciosa (showy milkweed) in a floating treatment wetland system (FTW) and evaluated the nitrate uptake capacity of these plants grown in three different nitrogen concentrations i.e., 10, 20, and 30 mg/L and two water temperatures of 75°F and 85°F. Increasing water temperature increased growth index for both species and increased dry weight for Asclepias speciosa. However, for Helianthus maximiliani, increasing temperature had a lesser effect on total dry weight. The accumulation of nitrate nitrogen in plant tissue was higher in Helianthus maximiliani at the nitrate nitrogen concentration of 20 mg/L under both temperature treatments. However, in Asclepias speciosa, the accumulation of nitrate nitrogen in plant tissue was higher at the high temperature treatment of 85⁰F and 20 mg/L nitrate nitrogen concentration. The nitrate nitrogen uptake from both plants in this study indicated suggests that Helianthus maximiliani ‘maximilian sunflower’ and Asclepias speciosa ‘showy milkweed’ can be grown as FTW and be used to remove nitrogen from a nursery retention pond.

Iron (Fe) and Zinc (Zn) are two micronutrients which are crucial for human health and proper functioning of the circulatory, endocrine, immune, nervous, and reproductive systems. Deficiencies in dietary Fe and Zn can result in numerous illnesses and disorders and are among the most prevalent micronutrient deficiencies worldwide. There is an urgent need for improving the dietary intake of these micronutrients and a promising, quick, and effective improvement strategy is agronomic biofortification. Microgreens are an ideal and versatile choice for meeting nutritional needs. They are nutrient-dense, have low phytic acid content, can be produced for a range of species, and have a relatively short growth cycle – making them a convenient biofortification target crop. Previous studies’ attempts towards the simultaneous biofortification of Fe and Zn have indicated their antagonistic interactions during uptake, where the increase of one mineral led to a decreased uptake of the other. However, limited information is available about the opportunity of enriching microgreens with both nutrients using fertigation. Therefore, in this study we aimed to assess the optimal combination of Fe and Zn fertilizer concentrations, provided via fertigation, to maximize their simultaneous accumulation in radish and sunflower microgreens without impairing yield and quality. Using a completely randomized block design setup, a factorial combination of FeSO4 (0, 20, and 40 mg/L of Fe) and ZnSO4 (0, 10, and 20 mg/L of Zn) was tested. Across both species, it was observed that fertigation using the treatment combination of 40 mg/L FeSO4 and 20 mg/L ZnSO4, (Fe40-Zn20), resulted in a substantial increase of both micronutrient levels. Compared to the untreated control, the Fe40-Zn20 treatment increased Fe and Zn accumulation by about 200% and 900%, respectively, in radish microgreens, and about 180% and 600% in sunflower microgreens. Additionally, this treatment resulted in minimal yield reduction. Fresh and dry biomass decreased by approximately 23% and 9%, respectively, in radish microgreens, and 38% and less than 1% in sunflower microgreens. Although increasing both Fe and Zn content proves to be a challenging endeavor, this study revealed evidence of an optimal combination of selected Fe and Zn sources and application rates that, via fertigation, was effective in their simultaneous enrichment in two microgreen species.

Evaluation of Native Azaleas for Container Production in the Mid-Atlantic - William Errickson
Facilitating Pollinator Conservation in Agriculture: Understanding Grower Needs in Obtaining IPM Certification - Madison Love
Relationship between Soil Water Content, Quantum Efficiency, Stomatal Conductance and Stem Water Potential in Salvia guaranitica ‘Black and Blue’ - Lindsey Trinkle
Effect of Coconut Coir and Biochar Media on Ornamental Plant Growth and Nutrient Leaching - Saroj Burlakoti
Physiological and Morphological Characteristics of Marigold Exposed to Different Ratios of Blue Light and Red Light - Anju Chaudhary
Responses of Three Ornamental Species to Saline Water Irrigation - Zirui Wang
Field Performance of Penstemon Species under Deficit Irrigation - Zirui Wang
Responses of Calamagrostis ×acutiflora under Deficit Irrigation - Zirui Wang

Deciduous azaleas (Rhododendron spp.) are native to the Eastern United States and have potential for increased adoption in the ornamental nursery and landscape market. However, plant availability is currently limited and trials on the growth and performance of each species are lacking. Furthermore, seed propagation is the common production method for native azaleas, which can result in phenotypic variation and a longer period of time to produce a saleable product, relative to vegetative propagation. Under optimum growing conditions, native azaleas can be low-input plants with minimal insect and disease issues. However, they can also be susceptible to summer heat stress and require well-drained soils and partial-shade similar to their indigenous growing environments in order to thrive. To determine which species may be most well-adapted to typical container nursery production practices, container trials were established to evaluate nine different species of native azaleas, including R. arborescens, R. atlanticum, R. austrinum, R. canescens, R. cumberlandense, R. flammeum, R. periclymenoides, R. prunifolium, and R. vaseyi, grown in both full sun and 50% shade conditions. Seed-grown one-year old liners of each of the nine different species were established in one-gallon containers and evaluated for growth rate and physiological characteristics, such as leaf chlorophyll content and normalized difference vegetation index (NDVI), comparing plants grown in full sun vs. 50% shade. In year two, bloom dates and number of blooms per plant in full sun vs. 50% shade were compared. R. atlanticum demonstrated the greatest potential for commercial production, especially when grown under 50% shade conditions, based on growth rate and average number of blooms per plant. These results suggest that R. atlanticum may be a reliable species of native azalea for growers to commercially produce for this growing market segment, while other species may still have potential, albeit with additional attention to their specific production requirements.

Due to global concerns over the decline in pollinator populations, Walmart U.S. has initiated a policy requiring all produce and floral products sold in stores to be sourced from vendors who have obtained an Integrated Pest Management (IPM) certification from an approved third-party organization by 2025. The certification process for growers entails comprehensive documentation of operational practices, pesticide use and mitigation, and evaluation of on-farm pollinator habitat. However, this process is cumbersome for growers to conduct alone, necessitating assistance from a third-party such as Extension agents and staff. Furthermore, identifying and expanding existing pollinator habitat is often unfamiliar to growers, presenting a significant barrier in the application process and hindering the expansion of pollinator habitat. This project seeks to assess the needs of growers in navigating the IPM certification process and understanding the barriers they face. Future work will include the development of accessible consulting services that supports North Carolina growers throughout the certification process while also equipping them with necessary skills and knowledge to enhance and expand pollinator habitat.

Perennials are an important component in north-central Texas landscapes, providing color and foraging for local pollinators. However, severe summer drought and a rapidly growing urban environment forces limitations on water availability for landscape irrigation. Therefore, we need to evaluate the impact of deficit irrigation on landscape plant performance. Salvia guaranitica ‘Black and Blue’ is a perennial known to perform well in north-central Texas summers, and it attracts numerous pollinators, including bumblebees, butterflies, and hummingbirds. Twelve beds were created in four blocks, with three beds per block and one plant planted per bed. Within each block, irrigation was applied at one of three levels, 60% of evapotranspiration (ET), 30% of ET and no irrigation. Soil moisture monitors [time domain reflectometry (TDR), 10HS, Onset Computer Corp., Bourne, MA] and a handheld moisture meter (TDR, Fieldscout 350, Spectrum Technologies, Aurora, IL) were used to measure water content by volume (Θv). Quantum efficiency (ΦPSII) and stomatal conductance (gs) were measured using a fluorometer/porometer (LI-600, LiCor Corp., Lincoln, NE), and stem water potential of each plant was measured using a pressure chamber (Model 615, PMS Instrument Company, Albany, OR) on a weekly basis. Surprisingly, soil moisture levels in the 30% treatment (0.10 m-3·m-3) were the lowest, with 60% at 0.25 m-3·m-3) and no irrigation at 0.14 m-3·m-3. Quantum efficiency was similarly lower in 30% (0.60), compared to 0.72 and 0.69 for the 60% and unirrigated plots, respectively. Stomatal conductance was similar across all treatments. Stem water potentials were highest in plants receiving 30% (800 kPa), compared to 380 kPa in 60% and 360 kPa with no irrigation. Across all treatments, plant performance was correlated to soil water content, (ΦPSII P=0.03, r=0.24; gs P=0.05, r=0.22; kPa P=0.003, r=-0.33). Based on this study, Salvia guaranitica ‘Black and Blue’ should be irrigated at 60% of ET for best plant performance during summer heat and drought.

The growing demand for container ornamental plants opens new opportunities for nurseries to expand their business. However, expecting to improve plant quality, growers often overapply fertilizer and water. Excessive fertilizer application and overwatering can result in nutrient leaching and runoff. In addition, growers heavily rely on unsustainable sphagnum moss as a medium for growing their plants. Replacing sphagnum moss with coconut coir may increase production sustainability, and incorporating biochar may have potential to adsorb excess nutrients, thus lowering fertilizer concentration in leachate. In this study, we explored the suitability of using various mixtures of coconut coir and biochar for growing goldenrod, lavender, and chrysanthemum plants for two growing seasons. Results indicated that utilizing pine bark and coconut coir did not hinder plant growth and development compared to a traditional mixture of pine bark and sphagnum moss for any of the plants studied. Also, inclusion of 10% biochar did not enhance growth, nor did it reduce nitrate nitrogen and phosphorus concentration in container leachate. Biochar did not reduce nutrient leaching in this study. However, coconut coir was found to be a suitable substitute for sphagnum moss in container nursery production.

Light plays a crucial role in regulating various aspects of plant growth, development, and metabolism. The absorption spectra of photosynthetic pigments are primarily concentrated in the blue (400-500nm) and red (600-750nm) regions of light, making these wavelengths particularly influential in plant morphogenesis and photosynthesis. Varying the ratios of blue to red light can produce distinct morphological and physiological outcomes in plants. Blue light enhances photosynthetic activity and promotes more compact and robust growth, while red light encourages rapid growth and flowering. These specific combinations can be optimized for desirable traits in ornamental plants. This research aims to evaluate the effects of different combinations of blue and red light on the physiological and morphological characteristics of marigold (Tagetes erecta) ‘Crackerjack’. Seeds were sowed in Metromix 820 potting mix and placed on a misting bench for germination. After germination, seedlings were subjected to three different light spectra: 10% blue and 90% red LEDs (10¬B90R), 25%blue and 75% red LEDs (25B75R), and 50% blue and 50% red LEDs (50B50R) maintained using a spectrometer (StellarNet Inc.). A 90% shade cloth was used in each treatment to prevent the effect of outside light. The photosynthetic photon flux density (PPFD) was maintained at 150 µmol.m-2.s-1 and the photoperiod was maintained at 12 h light and 12 h dark. After four weeks, various physiological and morphological parameters were assessed in five destructively harvested seedlings per treatment. We found that seedlings grown under the 25B75R treatment exhibited greater height in comparison to those under the 50B50R spectrum but similar to seedlings under 10¬B90R. Stomatal conductance (gs) and photochemical efficiency (Fv/Fm) were higher under 50B50R than in 25B75R but comparable to those in 10¬B90R. Additionally, the SPAD and NDVI values, which indicate chlorophyll content and overall plant health, were highest under the 50B50R treatment. However, leaf area, total fresh weight, and total dry weight showed no significant differences among the treatments.

Deficit irrigation plays a crucial role in water conservation in urban landscapes. Calamagrostis ×acutiflora (feather reed grass) is an ornamental grass known for its neat clumps, golden plumes, and fast growth. It is gaining popularity in urban landscapes across arid and semi-arid regions in the United States. However, little is known about its responses to deficit irrigation. A field study was conducted in 2022 and 2023 at the Utah Agricultural Experiment Station’s Greenville Research Farm in North Logan, UT, to assess the effect of irrigation frequencies on the growth of feather reed grass. Reference evapotranspiration (ETo) data from a weather station in the Utah AgWeather System, Utah Climate Center, Logan, UT, was used to determine the irrigation frequency for each treatment. Four hundred plants were transplanted into the field plot, with twenty plants in each of the twenty 2 by 2-meter plots. Eighty plants within four plots were randomly assigned to one of five irrigation treatments, controlled based on 80%, 60%, 40%, 20%, and 0% ETo. Two harvests were conducted on 30 Sep 2022 and 3 Nov 2023, during which plant height, number of tillers, and biomass were recorded. Plants height, number of tillers, and biomass for both years exhibited a linear and quadratic increase as the irrigation frequencies increased from 0% to 80% ETo. In addition, the linear relationship between irrigation treatments and grass height became less distinct in 2023, although grasses irrigated at 80% ETo were taller compared with those at lower irrigation levels. Based on the results, an irrigation frequency of 40% to 60% ETo is recommended for feather reed grass to maintain optimal growth.

Water-efficient landscaping can reduce water consumption without compromising the aesthetical appearance of urban landscapes. Penstemon, with more than 250 species available in a spectrum of colors, is a popular choice in xeriscape designs and water-wise gardening due to its ability to thrive in dry conditions while providing attractive visual appeal. However, limited field trials have explored the responses of penstemon under deficit irrigation. This study, conducted at the Utah Agricultural Experiment Station’s Greenville Research Farm, North Logan, UT, USA, from 30 Jun to 31 Oct 2023, was to investigate the overall appearance and canopy temperature responses of three penstemon species: Penstemon barbatus (Cav.) Roth ‘Novapenblu’ (Rock CandyTM blue penstemon), Penstemon pinifolius (pineleaf beardtongue), and Penstemon strictus (rocky mountain beardtongue), under three irrigation frequencies. Reference evapotranspiration (ETo) was utilized to control irrigation frequencies. Eight plants of each penstemon species were randomly assigned to one of three deficit irrigation treatments, calculated based on 80% ETo (high), 50% ETo (moderate), and 20% ETo (low). A monthly evaluation of overall appearance was conducted. Top-view infrared images of plant canopies, from which canopy temperature can be calculated, were captured using a thermal camera. Results revealed that higher irrigation frequency led to better overall appearance, with some variability observed among species and months. Moreover, increased irrigation frequency correlated with lower canopy temperatures, displaying species-specific responses. Further observation is needed to compare the responses of P. strictus, P. pinifolius, and P. barbatus under field conditions.

Water scarcity is a pressing issue in Utah and the Intermountain West, leading to a growing interest in exploring alternative water sources for landscape irrigation. However, alternative water often contains elevated levels of salts, such as sodium chloride (NaCl), which can negatively impact plant growth and appearance. This study investigated the effect of saline solutions on the aesthetic value, growth, and stomatal conductance of three ornamental species: Hibiscus syriacus ‘JWNWOOD4’ (Pink Chiffon® rose of sharon), Viburnum carlesii ‘Spiro’ (koreanspice viburnum), and Vitex agnus-castus ‘SWVACSD’ (lilac chastetree). Plants were irrigated weekly with a nutrient solution at an electrical conductivity (EC) of 0.9 dS·m-1 and saline solutions at 5.0 or 10.0 dS·m-1 for eight weeks. Visual quality was rated weekly using a reference scale ranging from 0 to 5 (0 = dead, 5 = excellent without foliar salt damage). Half of the plants per treatment per species were destructively harvested on 16 Aug (first harvest), and the remaining plants on 4 Sep (second harvest). Plant growth parameters and stomatal conductance were recorded at harvests. Foliar salt damage, such as leaf discoloration and necrosis, was prominently observed in plants, particularly in Viburnum carlesii subjected to elevated EC irrigation. Higher stomatal conductance was consistently observed in all plants irrigated with nutrient solution compared to those under saline irrigation. Interestingly, the salinity treatment did not significantly affect the growth of Vitex agnus-castus, indicating its high salt-tolerance. Notably, Viburnum carlesii displayed higher sensitivity to salinity stress compared to the other two ornamental species. These findings highlight significant variations in responses among the ornamental plant species under saline irrigation at varying EC levels, emphasizing the necessity of employing appropriate alternative water usage strategies.

Nutsedge Management Through Soil Steaming - Shaun Broderick 
Early Season Soil Tarping Impacts on Weed Pressure and Onion Production in Eastern South Dakota - Hannah Voye 
Associations Among Crop/Weed Management Practices and Environmental Factors Highlight Challenges Facing U.S. Snap Bean Production  - Martin Williams 
Impact of Early Season Tarping on Soil Conditions and Weed Populations in North Central United States Vegetable Production Systems - Carly Strauser
Applying Advanced Lighting Practices for Vegetable Propagation - Rose Seguin
Evaluating the Effect of Three Algae Extracts Application on Three Crops Growth and Yield in Hawaii - Amjad Ahmad
Using the Feekes Growth Stage Scale to Predict the Carbon to Nitrogen Ratio of Cereal Cover Crops - Eric Brennan
Evaluating the effect of fertilization and controlled-water deficit on growth and yield of compact vegetable plants - Michael Fidler

Soils host weeds, pathogens, and insects that can cause crop damage and reduce yield. Many methods have been developed to reduce these pressures within the soil, including soil solarization, chemigation, anaerobic soil disinfestation, and soil steaming. We have utilized soil steaming to reduce weed seeds and soil infestation in high tunnel and field tomato (Solanum lycopersicum) production. While it successfully reduces most weed species and southern blight (caused by Athelia rolfsii) in tomatoes, the emergence of nutsedge (Cyperus spp.) in soils with established populations can increase after steaming. Our research goal was to evaluate the efficacy of various soil preparation methods prior to steaming to allow the steam to penetrate the soil and target nutsedge directly. Except where noted, the field was first chisel plowed, disced, and then shaped into 2-foot-wide by 6-inch-tall beds. We compared 8 preparation methods for controlling nutsedge: a no-till control, herbicide control using S-metolachlor and halosulfuron-methyl, 6-inch-tall bed size, 12-inch-tall bed size, chisel plowed row, black plastic mulch, 4-inch-deep trenches on no-till, and 6-inch-deep trenches on no-till. Four trenches were cut into the soil with a soil trencher for each plot. Four replicates were included in a completely randomized design. Half of each bed was steamed until temperatures reached 160 °F, 4 inches deep, except for the herbicide beds and mulched beds, which were left unsteamed. Four sets of temperature probes were placed 12, 8, 6, and 4 inches deep in the soil and temperatures and used to monitor temperature changes in steam soils over time. Nutsedge coverage was visually estimated by placing a 1 by 6-foot rectangular PVC frame in each row over a representative section. 12-inch-tall beds had nearly 100% nutsedge coverage, while 6-inch-tall beds had nearly 50%. Herbicides reduced nutsedge coverage to 29%, and the plastic mulch reduced coverage to 8%. The steamed no-till, 4-inch trench, 6-inch trench, and chisel-plowed beds had no nutsedge emergence through the trial. The 6-inch-tall beds had lower temperatures at 6 and 8 inches deep than the other methods, which could account for the observed increases in nutsedge emergence post steaming. The time-consuming nature of soil trenching would make it impractical for most horticultural production settings; however, the chisel plow and no-till could be readily adopted. Determining effective methods to prepare the fields for soil steaming to reduce or eliminate nutsedge will make soil steaming a more viable method for organic farmers facing nutsedge pressures.

Cereals and other non-legume cover crops can help vegetable farms to reduce nitrogen leaching to ground water during rainy winter periods. A cover crop’s carbon to nitrogen ratio is an important metric that can help farmers better understand the nitrogen release dynamics from soil-incorporated cover crops. Cover crops with a lower C:N ratio (15:1) typically mineralize nitrogen when they are incorporated into the soil, whereas those with a higher C:N (25:1) usually immobilize nitrogen. But farmers need simple, reliable, field-based methods to predict a cover crop’s C:N ratio. Therefore, we evaluated the relationship between the Feekes growth stage scale and the C:N ratio of rye (Secale cereale L., ‘cv. Merced’) and triticale (X Triticosecale Wittmack, cv. ‘Pacheco’) cover crops in the Central Coast region of California. Over a hundred field samples of rye and triticale shoots were collected at various developmental growth stages from organic and conventional vegetable farms and planting date trials, across multiple soil types, planting times, row spacings, and plant densities. The Feekes scale was correlated with the C:N ratio of cover crop shoots of rye (r2=0.63) and triticale (r2=0.76). The transition from Feekes 9 (when the ligule of the flag leaf is visible) to Feekes 10 (‘boot’ stage) is roughly when the C:N ratio went from below to above 20:1. Regression plots were developed that illustrate the relationship between the Feekes scale and the C:N ratio. These results have practical implications for a new ground water protection regulation (Ag. Order 4.0) in California’s central coast region that incentivizes winter cover crops that are grown until the C:N ratio is 20:1 or more.

Snap bean production has decreased by ~30% recently due to an increase in imports and changing consumer preferences towards more fresh and frozen products. A major production concern is weed species that escape control, since they cause yield losses and can contaminate harvest loads. Coupled with changing weather patterns, snap bean processors and growers will have to adjust to these and future challenges. Field surveys were conducted to identify associations among crop/weed management practices and environmental factors on snap bean yield and weed density. From 2019-2023, snap bean fields throughout the major U.S. production regions were surveyed for weeds at harvest. Management records for each field were obtained from growers. Information on soil and weather conditions of each surveyed field also was obtained. In total 358 production fields were surveyed in the Midwest (Illinois, Iowa, Minnesota, Wisconsin), Northeast (Delaware, Maryland, New York. Pennsylvania), and Northwest (Oregon, Washington) regions. To determine associations among management and environmental variables on crop yield and weed density, the machine learning algorithm random forest was utilized. The models had 24 and 22 predictor variables for crop yield and weed density, respectively, and both were trained on 80% of the data with the remainder used as a test set to determine model accuracy. Partial dependence plots were used to visualize the change in response variables based on the most important predictors. The crop yield model had pseudo-R2 values of 0.56 and an accuracy of 74%. Higher average temperatures during early season growth, higher soil organic matter content, and planting midseason (June-July) predicted an increase in average crop yield. Meanwhile, excessive precipitation early in the season, high sand content of the soil, high temperatures at crop flowering and row cultivation predicted a decrease in crop yield. The weed density model had pseudo-R2 values of 0.55 and an accuracy of 81%. While row cultivation was associated with lower snap bean yield, it corresponded to a decrease in weed density, suggesting row cultivation had less-than-ideal selectivity between the crop and weed. Moreover, multiple spring tillage operations prior to planting predicted an increase in average weed density, implying that excessive tillage may favor emergence of weeds in snap bean. Over the coming decades, climate change-driven weather variability is likely to influence snap bean production, both directly through crop growth and indirectly through weeds that escape control practices that also are influenced by the weather.

Weed management is one of the biggest challenges vegetable growers face. Plastic mulch, herbicides, tillage, and hand-weeding are common ways vegetable growers manage weeds. These methods can be labor intensive, require specialized equipment, and cause environmental harm. Tarping is an alternative weed management method. Silage tarps or high-tunnel plastics are commonly used tarping materials; these are multi-functional tools that can be used for several years. Tarping facilitates stale seedbed weed management techniques by modifying the soil microclimate and promoting weed germination. After weed germination, opaque tarps can terminate weeds via occultation (lack of sunlight), whereas clear tarps terminate weeds by creating extreme temperatures. More information is needed for the type and timing of early-season tarp application for optimal weed control. The research was conducted at the Iowa State University Horticulture Research Stations in Ames, IA. This study examined three types of tarps: black, white, and clear, at three different durations: two, four, and six weeks prior to planting compared to a non-tarped control. Clear tarp and control treatments were cultivated at the time of tarp removal prior to planting. Soil temperature was recorded at 5 centimeters depth for 6-week tarp treatments. Early-season clear tarping did not elevate temperatures enough to terminate the majority of weeds. However, black and white tarps created a weed-free planting bed. Average soil temperatures underneath the clear tarp were the warmest (21.8ºC), followed by black tarp (15.1ºC). White tarp treatments (11.7ºC) had a lower average soil temperature than treatments with no tarp (14.8ºC). Two weeks following tarp removal, six-week clear tarp treatments had a higher percent weed cover than black and white tarp treatments measured using Turf Analyzer, a digital photo analysis software. Differing soil temperatures did not significantly impact soil microbial biomass carbon. The two-week white tarp had significantly higher soil microbial biomass nitrogen than all other treatments except four-week clear tarp. There was no effect of tarp type or duration on onion crop yield. These results indicate that the use of white and black tarps can be a feasible alternative weed management method in North Central vegetable production systems.

Propagation greenhouses produce a wide range of crops, each presenting unique responses to light quality and quantity. With dynamic LED lighting solutions now available and proven to be viable over large acreages, propagators can tailor their lighting protocols to each crop with regards to zone management, photoperiod, spectrum and intensity. The effects of light quality and quantity on plant morphology and growth are well documented and while the exact impact is not generalizable across all crops and varieties, certain themes hold true. For example, high levels of blue light are generally associated with compact plants and thick, waxy leaves. In contrast, high levels of far-red light can cause etiolation in multiple species through the shade avoidance response but enhances photosynthesis and growth when combined with red light. Given the high importance of crop morphology in propagation, dynamic Dynamic LED lighting has been used to develop advanced lighting protocols in the propagation of fruit, vegetable and ornamental crops. In the production of cucumber transplants, applying high levels of blue light and a long photoperiod effectively slows the growth of cucumber transplants at the end of the propagation cycle, a strategy which proved useful to a propagator looking to delay transplant delivery per the client’s request. Concretely, the combination of high blue levels and a long photoperiod slowed crop growth, prevented tendril development and restricted plant stretching. Further, the use of high-blue treatments over young leafy greens effectively reduced plant height by 2-3 cm and produced stronger plants. Another trial focused on the production of strawberry tray plants found that a balanced light spectrum produced more stolons (i.e., daughter plants) while a blue-enriched spectrum produced significantly more leaves. In the production of ornamentals, dynamic lighting can be used to reduce the greenhouse’s reliance on plant growth regulators (PGRs), enhance leaf or petal coloration and trigger bud formation. In red-leafed varieties, controlled light-induced plant stress through spectral and/intensity adjustments have proven effective at stimulating the production of red pigments and enriching the leaves’ hue. Results from various commercial and research trials demonstrate benefits of dynamic LED lighting in the propagation of horticultural and ornamental crops alike. This presentation presents data from the aforementioned case studies among others.

Food- and nutritional-security are among the highest concerns for Hawaii residents. The state imports about 85% of the consumed food and there’s roughly two-week worth of food locally at any given time. Local food production is costly due to high inputs cost. Algae extracts are known to supports plants' flowering and fruiting, increasing plant nutrient uptake, enhancing resistance and recovery from plant stress events, and increasing nutrient use efficiency and fertilizer assimilation. Three different algae extracts (Afrikelp, Acadian, and Kelpak) were evaluated for their effect on growth and yield of bush bean, bell pepper, and tomato in a randomized complete block design (RCBD) with 5 blocks. The algae extracts were applied 5 times during each growing season. The algae extracts were applied at dilution rate of 1:100 with a week between applications for the bush bean crop and two-week intervals for bell pepper and tomato crops. The results showed a highly significant (p < 0.01) increase in the three crops yield under all algae extracts compared to control (water only) treatment. The results also showed there was a significant (p < 0.05) difference between the algae extracts with highest yield recorded under Afrikelp extract compared to Acadian and Kelpak. The yield increase reached between 150-300% compared to control treatment.

Onions are a globally popular kitchen staple, not only for their flavor, but also their nutritional value. According to the Agricultural Marketing Research Center, onions are the fourth most consumed fresh vegetable in the United States. To bring this valued crop to our kitchen tables, quality onions must be produced in high quantities to meet consumer demands. Since they are especially susceptible to weed competition due to their minimal canopy cover, weed management is an important consideration for onion production. One weed management tool is soil tarping. This study evaluated the impact of two types of tarping (solarization and occultation) and duration of tarping (6-, 4- and 2-weeks) on weed control in Patterson and Candy onion production. Field experiments were conducted during the 2023 growing season in Brookings, South Dakota. Solarization was conducted using clear tarps secured with sandbags and buried edges. Tarps were placed in April and May at respective weeks before removal on May 30. Immediately following tarp removal, each plot was tilled, and rows of onion transplants were planted. Occultation was evaluated using white side up and black side up silage tarps, both applied at respective weeks before removal and onion planting. Each treatment plot filled a twenty-four by ten-foot area. A randomized complete block design with four blocks and ten treatment plots per block including a control with no tarp was established. Response variables for data collection included weed type, height, and biomass as well as onion yield. All tarping treatment plots resulted in less weed pressure than the control at tarp removal. Broadleaf weed count collected during the growing season was different among tarp treatments (p=0.03). Data collected June 12 showed 6-week clear tarp to have 67% less broadleaf weed count per acre than the control, and 74% less than the 4-week black tarp. There was no difference in onion yield due to tarping treatment. This may have been due to biweekly weeding events that evened out treatment effect on weeds over the growing season. There was, however, a difference in yield between Candy and Patterson onion cultivars (p=0.02). Candy averaged a marketable count of 19 of 48 planted onions while Patterson averaged a marketable count of 36 of 48 onions planted. Soil tarping may be an effective option for farmers to reduce early season weeds in onion production, however, it should be used alongside other management strategies to obtain a viable yield.

Sales of compact vegetable bedding plants for the home-gardening market segment are increasing. However, production guidelines for these new crops are limited. Our objective was to assess the effect of fertilizer use and controlled-water deficit (CWD) on plant growth during production, and after-production effects on fruit yield. ‘Siam’ tomato and ‘Basket of Fire’ pepper plants were grown in a greenhouse for 4 and 6 weeks, respectively, using 10-cm containers. Half of the plants received a water-soluble fertilizer once a week, and the other half were irrigated with tap water only, relying on the starter fertilizer charge in the substrate (EC = 0.9 mS·cm−1). Plants were irrigated when the substrate volumetric water content (VWC) reached 0.15, 0.30, 0.45, or 0.60 m3·m–3. After the experiment, plants were transplanted into 20-cm containers, top-dressed with controlled-release fertilizer (CRF), and grown for another 10 weeks to evaluate carryover treatment effects. Plants that did not receive fertilizer were shorter and had a lower shoot dry mass (SDM) than those that were fertilized, regardless of species. Shoot height of tomato followed a quadratic trend in response to CWD, which peaked at 0.45 m3·m–3, whereas SDM linearly increased with increasing VWC. No growth responses to CWD were measured for pepper. However, plants of both species that did not receive fertilizer looked chlorotic and had a lower chlorophyll concentration than those that were fertilized (15 and 32 µmol·m–2 for tomato and 15 and 27 µmol·m–2 for pepper, respectively). Plant greenness increased after applying CRF, suggesting that applying fertilizer right before shipping could increase quality of these plants when grown with limited or no fertilizer to control growth. After the carryover phase, differences in plant growth were maintained, and differences in yield was measured between fertilized and non-fertilized plants (56 and 48 fruits for tomato and 153 and 112 fruits for pepper, respectively). Our results show that growth and yield of compact tomato and pepper plants are affected to a larger extent by fertilizer use than by substrate VWC.

Leveraging the inherent genetic diversity conserved in plant resource collections is key to new crops, new cultivars, and adapted germplasm with improved traits that provide food security for a growing population, remain productive amidst rapid climate change, meet shifting consumer demands, and enhance sustainability and efficiency. The USDA National Plant Germplasm System manages large and genetically diverse plant collections representing crop plant species and many of crop wild relatives (CWR) that have significant impacts on crop production. In this Special Topic Session hosted by the Federal Partners Interest Group, scientists of the Agricultural Research Service (ARS) will discuss the current efforts and future perspectives on the restoration and utilization of germplasms and CWR at the USDA with a special focus on fruit, nut, and beverage crops.

Coordinator(s)

• Lisa Tang, USDA-ARS Appalachian Fruit Research Station, Kearneysville, WV, United States

Moderator(s)

• Lisa Tang, USDA-ARS Appalachian Fruit Research Station, Kearneysville, WV, United States
• Matthew Mattia, USDA-ARS U. S. Horticultural Research Laboratory, Fort Pierce, FL, United States

Speaker/Participant(s)

• Lisa Tang, USDA-ARS Appalachian Fruit Research Station, Kearneysville, WV, United States
  Introduction of the Federal Partners special session (5 mins)
• Gayle Volk, USDA, Fort Collins, Colorado, United States
  The USDA-ARS National Plant Germplasm System Strategic Plan: A roadmap to conserve and utilize U. S. plant genetic resources (15 mins)
  Summary: The USDA-ARS National Plant Germplasm System (NPGS) conserves more than 620, 000 accessions of plant genetic resources of crops and crop wild relatives which annually distribute 200, 000+ samples globally. As directed by the 2018 Farm Bill, an NPGS Strategic Plan was developed to address the backlogs in maintenance, characterization, and to enhance utilization. This presentation will provide information about the impacts of the NPGS and details about the NPGS Strategic Plan, which, when funded, will result in: 1) More plant germplasm maintained disease-free, securely backed up, and readily available; 2) Expanded knowledge of the intrinsic genetic variation and high-value traits in NPGS collections; and 3) New plant germplasm with valuable traits acquired, safeguarded and developed. This presentation is authored by Gayle M. Volk (USDA), Marilyn L. Warburton (USDA), Moira Sheehan (Cornell University), Christina Walters (USDA), Stacey Estrada (USDA), Glenn Hanes (USDA), Jim McFerson (USDA), and Peter K. Bretting (USDA-retired).
• Chris Gottschalk, USDA-ARS Appalachian Fruit Research Station, Kearneysville, WV, United States
  Into the wild: utilization of wild crop relatives the USDA ARS apple pre-breeding program (15 mins)
  Summary:
• Nahla Bassil, USDA-ARS National Clonal Germplasm Repository, Corvallis, OR, United States
  Crop wild relatives of temperate fruits at the Corvallis Genebank: Uses and prospects (10 mins)
  Summary:
• Michael Hardigan, USDA-ARS, Corvallis, OR, United States
  Crop wild relatives of temperate fruits at the Corvallis Genebank: Uses and prospects (10 mins)
  Summary:
• Tracie Matsumoto, USDA-ARS Daniel K. Inouye Pacific Basin Agricultural Research Center, Tropical Plant Genetic Resources and Disease Research Unit, Hilo, HI, United States
  Sub-Tropical/tropical Fruit, Nut, and Beverage Clonal Repository in Hilo, Hawaii (15 mins)
  Summary: The National Clonal Germplasm Repository for Tropical Fruit, Nut and Beverage Crops is located in Hilo, Hawaii and is a part of the National Germplasm Repository System and USDA ARS DKI PBARC Tropical Plant and Genetic Resources Unit. The repository is responsible for collecting, maintaining, evaluating, and distributing germplasm of tropical/subtropical fruit and nut crops. Crops include Pineapple (Ananas), Breadfruit (Artocarpus), Starfruit (Averrhoa), Peach palm (Bactris), Pili nut (Canarium), Papaya (Carica and Vasconcellea), Coffee (Coffea) Longan (Dimocarpus), Litchi (Litchi), Macadamia (Macadamia), Acerola (Malpighia), Rambutan and Pulasan (Nephelium), and Guava (Psidium). In addition to the field and greenhouse collections, we are actively investigating new methods to propagate and effectively manage the collections. We work to characterize the collection for resistance to pest and diseases and genetically characterize the germplasm to determine potential gaps for future collections.
• Qingyi Yu, USDA-ARS Daniel K. Inouye Pacific Basin Agricultural Research Center, Tropical Plant Genetic Resources and Disease Research Unit, Hilo, HI, United States
  Exploring germplasm diversity to understand the domestication process of papaya (15 mins)
  Summary: Papaya (Carica papaya L.), originating and domesticated in southern Mexico and Central America, is widely cultivated in tropical and subtropical regions due to its nutritional benefits and the commercially significant proteolytic enzyme, papain. While wild papaya yields small, seedy fruits with minimal edible flesh, domesticated papaya varieties can weigh over five pounds. Wild papaya populations are exclusively dioecious, whereas cultivated papaya is predominantly gynodioecious, although certain dioecious cultivars exist. In this study, we conducted whole-genome resequencing of 86 diverse papaya accessions, comprising 63 cultivars and 23 wild accessions. To identify regions undergoing selection during domestication and improvement, we scanned for areas exhibiting a drastic reduction in nucleotide diversity in cultivars compared to wild accessions. Our results suggest that papaya domestication involved selecting fruit quality traits such as taste and flesh color. Moreover, we re-sequenced the male-specific region of the Y (MSY) in 24 wild males and the hermaphrodite-specific region of the Yh chromosome (HSY) in 12 cultivated hermaphrodites. The Yh sequence is highly similar to one Y haplotype (MSY3), exclusive to wild dioecious populations in the north Pacific region of Costa Rica. The low MSY3-Yh divergence suggests that hermaphrodite papaya resulted from human domestication.