ASHS 2025 Conference

Effect of Microalgae Application on Yield and Nutrient Composition of Arugula Sam Pratt1*, Shivani Kathi1, Steve Phillips2, and Justin Moss1 1Department of Horticulture and Landscape Architecture, Oklahoma State University, Stillwater, OK, 74078 2Department of Plant and Soil Sciences, Oklahoma State University, Stillwater, OK, 74078 *Presenting author- Samatha.pratt@okstate.edu Chlorella (Chlorella vulgaris) has been used as a biofertilizer in horticultural crop production in controlled environment production systems. However, research gaps exist in the application of chlorella biofertilizer in field-based production systems. The goal of this research is to assess the impact of microalgae biofertilizers on crop productivity and nutritional quality of arugula grown in open-field using certified naturally grown production practices. To understand the impact of microalgae biofertilizer on soil nutrient and organic matter content, soil testing was done before and after treatment. Treatments included 50% and 100% nitrogen fertilizer and chlorella applied through foliar, soil and foliar soil application. Chlorella application began a week after transplanting. Data was collected on number of leaves per throughout the study and fresh and dry weight at harvest. Plant samples were analyzed for nutrient composition of leafy greens (chlorophyll, carotenoids, and mineral nutrients composition). Results show that soil applied chlorella was more effective application method regarding the overall impact on yield. Continued research on the addition of Chlorella in crop production can offer additional nitrogen sources for low chemical input and organic based production systems.

Organic vegetable farmers use a wide variety of nitrogen (N) fertilizers from commercial products (made from animal and seed meals) to manures and composts. These organic N sources must undergo mineralization and nitrification to become plant available inorganic N (microbial processes). How much and when nitrogen becomes available can be highly variable dependent on product characteristics and local weather conditions, and this subsequent N availability can greatly impact yield. The objective of this study was to determine nitrogen mineralization, head timing, and overall yield from seven different organic fertilizer treatments on fall broccoli (Brassica oleracea ‘Castle Dome’). Studies were conducted over two years at the UGA Durham Horticulture Farm on certified organic land and organic fertilizers (with the exception of the control) were applied to provide a rate of 134 kg N ha-1. Fertilizers ranged from processed animal meals to composts and fresh poultry litter. Nitrogen mineralization was measured using in-situ soil cores and ranged from 0 (immobilization) to 100% of the N applied. Significant N was observed from the soil only treatment which provided on average 100 kg N ha-1 over the growing season. In both years, overall higher yields were observed with blood meal and lowest yields were observed with compost/control treatments. Fertilizer type impacted the timing of heading and overall harvest windows.

Nutrient and weed management are two of the biggest challenges in organic vegetable production systems. Anerobic soil disinfestation (ASD) is an effective method to manage the weeds and soil borne pathogens in organic production systems. In ASD, a carbon source is added to soil followed by watering to saturation and covering with plastic mulch to create anerobic soil conditions. Rendered animal and treated manure products have significant content of plant nutrients and carbon and can serve both as organic fertilizer and carbon source for ASD. A field experiment was conducted using three different carbon sources meat and bone meal (MBM; rendering product), MBM Sulfur and treated manure solids with objective to evaluate the effect of different carbon sources and their application rates on nutrient management and ASD in organic watermelon under traditional and novel charter next generation plastic mulch. We will be evaluating the treatment effect on soil cumulative anaerobicity, percent weed coverage, yellow nutsedge rhizome viability, plant vigor ratings, shoot and root biomass, periodic nutrient leaching, soil nitrogen and phosphorus content, plant tissue nutrient content (root and shoot), soil pH, soil C, N and P mineralization enzymes and soil microbial biomass. In results, MBM with sulfur at 150% recorded the highest cumulative anaerobicity and low weed coverage suggesting that it could be an excellent tool for soil nutrient management and weed control in organic production system.

This study presents the evaluation of ten organic cover crops on soil fertility and macronutrient accumulation within their biomass. Field trials were conducted at the organic farm of Tennessee State University using a randomized complete block design with four replications under National Organic Program (NOP) management practices. The cover crops assessed includes barley, crimson clover, daikon radish, field peas, hairy vetch, mammoth red clover, medium red clover, tillage radish, white clover, and winter rye. Each plot measured 16 ft x 7 ft within a whole plot size of 190 ft x 63 ft. Cover crops were sown using a seed drill, adhering to USDA and SARE recommended seed rates. Soil Samples were collected at a foot depth both before and after cover crops termination to analyze the variations in soil properties such as pH, phosphorus, potassium, calcium, magnesium, zinc, iron, manganese, boron, sodium, and organic matter. Aboveground biomass was clipped from 1ft2 quadrants across all replications, dried at 60oC for 72 hours. Samples were grinded to a fine powder using a 1100-watt Ninja blender and analyzed for nitrogen and carbon content using Near-Infrared Spectroscopy (NIRS). Results indicated that most of the cover crops increased soil organic matter, phosphorus, sodium, magnesium, and iron. In contrast, declines were observed in soil pH, potassium, manganese, calcium, boron, zinc. Significant differences were observed in the nitrogen and carbon accumulation among cover crops. Hairy vetch showed the highest nitrogen (4.24%) and carbon (46.62%) content, while barley and daikon radish had the lowest nitrogen (1.55%) and carbon (40.66%) content, respectively. The carbon to nitrogen (C:N) ratio ranged from 11:1 to 30.1:1, with legumes generally exhibiting lower ratios (11:1 to 15.3:1) demonstrating higher decomposition and quicker nutrient release. In contrast non-legumes had the higher ratios (25.4:1 to 30.1:1), suggesting slower nutrient release. These findings highlight the short-term impacts of different organic cover crops on soil fertility and nutrient cycling. The variation in macronutrient accumulation and C:N ratios provides practical insights for the growers in selecting appropriate cover crops to enhance soil health and support sustainable agricultural systems.

The increasing demand for sustainable agricultural practices has driven the adoption of organic farming and increased demand for organic transplants. However, transplant growth is often lower in organic fertilizers compared to conventional fertilizers. This is most likely caused by low nutrient availability in organic fertilizers. On the other hand, increasing organic application rates has the potential to induce salinity stress/toxicity. We hypothesize that biostimulants can complement organic fertilizers in crop production by enhancing nutrient uptake and increasing crop tolerance to abiotic stress and thus close the yield gap between organic and conventional fertilizers. In this study, we tested three biostimulants: humic acid and molasses (MicroLife Soil and Plant Energy) and two microbial based biostimulants with different beneficial microorganism populations (MicroGrow CM and MicroGrow Supreme). Four organic fertilizers were tested with biostimulants, two of which were animal-based fertilizers: Sustane (4-6-4, turkey manure) and Drammatic (2-4-1, derived from fish scrap) and two of which were plant-based fertilizers: Nature Safe (7-7-7, corn steep liquor) and Pre-Empt (fermented sugarcane molasses). After applying to peat-based substrate, we analyzed the leachate nutrient availability weekly. Both fertilizer and biostimulant affected available nutrient concentrations in substrate. Additionally, transplant performance was evaluated to determine the effect of biostimulant and organic fertilizer combination on transplant growth, mineral nutrition, and physiological responses. Transplant growth varied across the different combinations of biostimulants and organic fertilizers tested, suggesting potential interactions between these factors. Some biostimulant treatments, particularly in combination with specific organic fertilizers, showed a trend towards improved early growth compared to the organic fertilizers alone. These results showed synergistical effects between biostimulants and organic fertilizers, indicating the positive role of biostimulants in organic transplant production.

Increased concerns over the last several decades on environmental quality have stimulated farmers to accept organic farming as an alternative to inorganic agriculture. Muscadine (Vitis rotundifolia var. Summit) is native to the southeastern United States and has been cultivated for over 400 years. Muscadine and its products are highly nutritious and a good source of antioxidants and dietary fiber that have positive effects on health. Muscadine was grown on Memphis Silt Loam soil (Typic Hapludalph, silty, mixed, thermic). Three treatments of organic manures (cow-C; poultry-P; cow poultry-CP) with gypsum and pine mulch were applied in a CRD. Control received inorganic fertilizers and traditional cultural practices. Dolomitic lime was applied every 2 to 3 years to balance the soil pH of the soil and the pine needle was continuously applied as a thick mulch to bring down the soil pH to neutral and also to prevent moisture evaporation from basins where fresh animal waste was applied. This thick layer of pine needle mulch helped avoid irrigation even during the hottest summer. While strictly following the protocol, soil samples were collected and analyzed at Cornell Soil Health Lab, Cornell University, Ithaca, NY, after 17 years of continuous organic research with the same treatments. The experimental design for data analysis was a completely randomized design with three replications for each treatment. Leaf area index (LAI), percent canopy cover, stem diameter, and yield were higher in organic plants. There was no significant difference in diameter, length, and degree brix of the fruit. Soil compaction was always higher in control with lower soil moisture content and the compaction was lower in organic treatments due to higher level of organic matter content. Concentrations of nitrate-N and P were higher in the surface soil treated with organic manures, but there was no trend in N or P enrichment in the lower layers of the soil. A comprehensive assessment of soil health done by Cornell Soil Health Lab showed the following: physical aggregate stability 19.0 25, biological organic matter 4.0 85, biological ACE soil protein index 6.8 43, biological soil respiration 0.8 75, biological active carbon 747 90 and chemical soil pH 7.1 100 with an overall quality score of 72 (Excellent). The results suggest that the controlled application of animal and forest wastes in basins of fruit trees can be an agronomically and environmentally sound practice to increase yield and keep the soil and humans healthy.

Soil-borne bacterial pathogens pose a significant threat to organic onion production as there is a lack of effective pathogen control practices for both conventional and organic systems. Burkholderia cepacia (causal agent of sour skin) and B. gladioli pv. alliicola (causal agent of slippery skin) are prevalent throughout the onion growing regions of the U.S., including Georgia. Organic growers rely on cultural practices to combat soil-borne diseases, pests, and weeds. Plants in the Brassica family contain glucosinolates which undergo hydrolysis and produce isothiocyanate volatiles serving as a biofumigant. Biofumigation has shown to be successful at reducing diseases, but efficacy is dependent on pathogen, environmental conditions, cover crop biomass, and soil conditions. The objective of this study aims to determine biofumigation effect on soil-borne bacterial pathogens associated with Burkholderia spp. This study was conducted on organic certified land using B. juncea ‘Pacific Gold’ for mustards and A. cepa ‘Sweet Tule’ for short-day onion crop. Mustards were grown and terminated at flower initiation with biofumigation treatments including mustard incorporated into soil, mustard incorporated into soil and covered with polyethylene mulch, and a no mustard control. To evaluate effectiveness of biofumigation, measurements on weed seed germination and biomass, disease incidence/severity in bulbs, and onion yield were measured. Weed seed germination was evaluated before and after the incorporation of the mustards. Weed biomass was measured at multiple time points throughout the onion growing season. At harvest, onions were graded according to the USDA standards (Colossal, Jumbo, Medium, and Cull). Bulbs were evaluated for the presence of both diseases at harvest. Post-harvest evaluation of bulbs was also conducted. A 50 bulb sub-sample/plot/treatment was placed in storage (-2 °C, 70% RH) for a period of 90 days. After storage, bulbs were sliced, and disease incidence/severity was recorded. At mustard termination, dry biomass among all treatments averaged 4,540.5 lbs/acre. Eleven weeks after mustard incorporation, treatments with plastic mulch following mustard incorporation had significantly less weeds than the control treatments.

Organic produce sales have increased over time as many consumers are willing to pay a higher price for organically-grown produce compared to conventionally-grown. Previous research has shown that liquid organic fertilizers outperform substrate-incorporated organic fertilizers in containerized production with soilless substrates. Therefore, developing new production protocols with water soluble organic fertilizers may increase yield and provide easier nutrient management. The objective of the current study was to identify water-soluble organic fertilizer combinations for growth and development of cucumber, Cucumis sativus ‘Picolino F1’, grown in a 40:60 wood fiber : coir substrate for ten weeks. Five fertilizer treatments were: molasses-based Pre-Empt (PE) at either 120 or 170 mg.L-1 nitrogen (N) in combination with 100 mg.L-1 calcium (Ca) from either calcium chloride (CaCl2) or FoxFarm’s Cal-Mag. A synthetic fertilizer treatment (Hydro-Gro Vine; N: 4.40% - P: 13.00% - K: 34.00% and calcium nitrate) was included as a control. The Cal-Mag 170 mg.L-1 N treatment had a similar yield to the control. However, there was no significant difference between all organic treatments for growth parameters measured. Additionally, leaf tissue analyses revealed boron increased by 22% to 37% and manganese by 37% above the sufficiency range for most of the organic fertilizer treatments. Meanwhile, N and potassium (K) concentration dropped below the required range by 45% and 49%, respectively, in all organic treatments. Future experiments will identify sources of supplemental N and K with the goal of supplying sufficient levels of all macro and micronutrients using water soluble organic fertilizers.

Organic materials such as meat and bone meal (MBM; rendering product) and treated manure products can be excellent fertilizers due to balanced availability of nutrients. In this study, we investigated the influence of natural amendments (NAs), specifically sulfur and neem oil, on nitrogen (N) mineralization dynamics from MBM and treated manure solids upto 63 days of incubation under controlled environment at 4 different time points (7th, 21st, 35th and 63rd days). Soil incubation experiments revealed distinct mineralization patterns between MBM and treated manure solids. MBM exhibited a faster N mineralization rate compared to treated manure solids. MBM treated with sulfur (25% of N) showed the highest net N mineralization rate (49.83%) as compared to untreated MBM (40.91%) by day 21. However, when MBM was amended with Neem oil (10% of N), the net N mineralization decreased significantly to 36.68% by day 21. There was no statistical difference observed between MBM, MBM with sulfur (25% of N), MBM with neem oil (10% of N) for net N mineralization at day 7. Similarly, treated manure solids with sulfur (25% N) non significantly reduced net N mineralization to 8.86% and 2.13% at 21 day and 7 days respectively. Further, we will be evaluating the effect of these treatments on soil biological health and C, N and P enzymatic activity. This comprehensive evaluation aims to provide insights into optimizing the use of natural amendments for strengthening nutrient management in organic agricultural systems.

Role of Chlorella Application on Yield and Phytochemical Composition of Mustard Greens Sam Pratt1*, Shivani Kathi1, Steve Phillips2, and Justin Moss1 1Department of Horticulture and Landscape Architecture, Oklahoma State University, Stillwater, OK, 74078 2Department of Plant and Soil Sciences, Oklahoma State University, Stillwater, OK, 74078 *Presenting author- Samatha.pratt@okstate.edu Organic nitrogen fertilizers have lower percentage of nitrogen than their chemical counterparts. Furthermore, nitrogen from organic fertilizers tend to be less readily available. Chlorella (Chlorella vulgaris) has been used as a biofertilizer in horticultural crop production in controlled environment production systems due to its role in nitrogen fixation. However, research gaps exist in the application of chlorella biofertilizer in open-field production systems. The goal of this research is to assess the impact of microalgae biofertilizers on crop productivity and nutritional quality of mustard green grown in open-field conditions under 100% nitrogen and nitrogen-deficit (50%) conditions. Treatments included chlorella applied through foliar spray, soil application, and a combination of foliar and soil arranged randomized complete block design in four blocks. Data was collected on yield (i.e., marketable and total yield) and nutrient composition of leafy greens (chlorophyll, carotenoids, and mineral nutrients composition). Soil application of chlorella under 100% fertilizer rate was more effective application method for the overall impact on yield. The crops that received lower amount of fertilizer and chlorella treatment had the lowest yield. Future research should focus on addition of Chlorella in different crop production systems with different organic fertilizers for additional nitrogen sources in low chemical input and organic based production systems.

With the goal of elucidating the influence of anaerobic soil disinfestation (ASD) on organic strawberry production, plant growth responses of strawberry cultivars to ASD treatments under Florida sandy soil conditions were evaluated in this study across two locations. In both locations (Balm and Citra), a split-plot design with four replications was used in the field trial with the ASD treatment as the whole plot factor and the strawberry cultivar as the subplot factor. The three-week ASD treatments consisted of 13.9 m³/ha molasses combined with Everlizer 3-3-3 (a heat-processed poultry manure organic fertilizer) at either 9.5 (ASD1) or 14.25 Mg/ha (ASD2) in comparison with the no ASD control, while the strawberry cultivars included ‘Ember’, ‘Encore’, ‘Florida Brilliance’, ‘Florida Medallion’, ‘Florida Pearl’, and ‘Florida127’. Destructive sampling was conducted at mid-season and final harvest. Significant effects of ASD treatment and strawberry cultivar were observed for most measured traits, with no significant interaction observed. Across locations and plant stages, ASD treatments significantly enhanced shoot fresh weight and dry weight, crown diameter and number, and leaf number relative to the no ASD control. At Balm, ASD2 increased shoot fresh weight and dry weight by 21% and 9%, respectively, compared with the no ASD control at final harvest. Similar trends were observed at Citra, where ASD2 resulted in higher shoot fresh weight and dry weight by 29% and 31%, respectively, in comparison with the control. In contrast to the no ASD control, both ASD treatments led to greater crown diameters and leaf numbers. At Balm, ‘Florida127’ produced the highest shoot biomass and leaf count, while ‘Florida Brilliance’ maintained the largest crown diameter and high shoot biomass across plant stages. At Citra, ‘Encore’ and ‘Florida Brilliance’ exhibited the highest shoot biomass at final harvest. The relationship between plant growth measurements and fruit yield components will be further examined in the follow-up analysis. Collectively, these results provide a physiological basis for selecting strawberry cultivars for organic systems and understanding genotype by soil treatment interactions toward exploring the linkage between soil health, plant health, and crop productivity.

Cabbage (Brassica oleraceae var. capitata) is a cool-season cash crop impacted by changing climates and hot summers. Fall-planted cabbage is a common practice hindered by warm-season weed competition during transplanting. This 2023 and 2024 study at the SDSU Southeast Research Farm, Beresford, SD, USA, investigated the impact of established clover living mulch on growth and yield of three fall cabbage varieties with different maturity periods. The varieties selected were Farao (65 DTM), Famosa (81 DTM), and Deadon (105 DTM). One year prior to cabbage planting, three clover cultivars were established: ‘Domino’ white clover (Trifolium repens), ‘Aberlasting’ white x kura clover (T. repens x ambiguum), and ‘Dynamite’ red clover (Trifolium pratense) which were compared to bare-ground control plots. Within each clover whole plot there were four in-row soil management subplots (till, till landscape fabric, no-till, no-till landscape fabric). Combinations of clover, soil management, and cabbage variety were compared for cabbage health, weed suppression, and marketable yield. Harvested cabbage heads were graded in accordance with the USDA Marketable Standard for cabbage cash crop production. Weed biomass decreased as the season progressed and mid-season drought conditions decreased clover growth. The in-row soil treatments demonstrated significant differences for clover and weed biomass accumulation (p < 0.0001). Regardless of variety, cabbage yield and transplant survival decreased within all no-till treatments; this was often due to very small and soft heads. ‘Fararo’ and ‘Famosa’ varieties matured faster than ‘Deadon’, resulting in the cash crop outcompeting weed and clover competition. Clover treatments had the highest impact on the yield of US Number 1 marketable heads (p = 0.02). Cabbage yield within the US Commercial and Unmarketable categories were not impacted by the clover treatments (p = 0.4 and p = 0.06, respectively). The impact of soil management treatments varied depending on the clover variety and cabbage variety combinations. The findings of this study suggest that clover living mulch systems reduce weed competition, minimizing farmers’ workload throughout the season. Within the planting beds, utilization of landscape fabric within no-till treatments is recommended to guard against yield loss. Use of tillage produced marketable crops for all cabbage varieties, yet yield depended on the clover and cabbage variety combination. Organic farmers who grow cabbage within a living mulch system could utilize the living mulch as a benefit for weed suppression in pathways but need supplementary strategies to optimize yield production within the crop row.

As the demand for organic products increases so does the need of organically managed land. In the southeast, where affordable and arable land has become scarcer and more expensive, organic farmers can choose to transition derelict farmland and old pastureland systems to expand current or begin new operations. However, this marginal land is commonly in need of fertility inputs and dominated by perennial weed species. The transition process can prove to be very time and effort consuming. Through the use of no-till drill seeded cover crops, poultry litter applications, and organic fertilizer applications farmers could reduce the thresholds for transitions while potentially reducing weeds, adding instant fertility, and helping build soils for quick turnaround of vegetable cash-crops. Therefore, the objective of this field study was to determine the effects of no-till drill seeded summer cover crops (Sorghum-Sudangrass and Vigna unguiculata) and tarping, with and without the addition of poultry litter, on subsequent fall broccoli production in Georgia. This was a two-year field study on broccoli with the first implementation taking place in the fall of 2023 and the second in the fall of 2024. No-till drilled cover crops and tarps were applied/planted in early May both years with and without the application of poultry litter in a randomized complete split block design. Cover crops were then flail mowed and incorporated in early August both years. Plots were rototilled the first week of September and Brassica oleracea var. italica cv. Belstar was planted with 0.45-m in row spacing in two rows on 0.18-m beds. Broccoli was harvested, counted, and separated into marketable yield or unmarketable yield. Soil cores were taken throughout both the cover crop and cash crop season with measurements of soil nutrients, inorganic nitrogen, and nitrogen mineralization potential being outlined. In 2023 and in 2024 plots that received the combined treatments of silage tarps, poultry litter, and organic fertilizer had the highest marketable yield average of 10013 kg/ha and 8623kg/ha. In 2023 the plots that received the treatments of sudex, no poultry litter, and no fertilizer preformed the poorest in terms of marketable yield, garnishing an average of 2429 kg/ha; while in 2024 the plots that received a silage tarp, no poultry litter, and no fertilizer preformed the poorest with an average marketable yield of 5614 kg/ha.