Assessing Anaerobic Soil Disinfestation for Improving Weed and Soilborne Disease Management in High-tunnel and Open-field Salad Green Production

Progress report for GS20-221

Project Type: Graduate Student
Funds awarded in 2020: $16,499.00
Projected End Date: 08/31/2022
Grant Recipient: University of Florida
Region: Southern
State: Florida
Graduate Student:
Major Professor:
Dr. Xin Zhao
University of Florida
Expand All

Project Information

Summary:

In response to national and local consumer demand, organic crop production in Florida has expanded during the last decade. In recent years, high-tunnels have emerged as a protected production system increasingly used by Florida organic growers because of their utility for season extension of high-value vegetables and improvement of produce quality. As organic production in high-tunnel systems continues to expand, research is warranted to guide producers in terms of pest and nutrient management. One method which has proved effective against several soilborne diseases across a wide range of horticultural crops and environments and shows promise as a weed management strategy is anaerobic soil disinfestation (ASD). ASD is a preplant method based on creating anaerobic soil conditions by incorporating labile carbon sources, irrigating to fill the soil pores with water, and covering the soil with a gas impermeable barrier. ASD promotes soil microbial shifts toward facultative and obligate anaerobes which produce short-chain organic acids and volatile compounds that are likely toxic to and inhibit weed seed germination. While previous studies have focused on disease management and the underlying mechanisms, limited field studies have investigated the effects of ASD treatment on soil and crop nutrient dynamics as well as ASD for managing weeds in high-tunnel systems.   

 

To our knowledge, limited field studies have been conducted to determine the impacts of ASD soil treatment on baby leafy green production and soil nutrient dynamics in organic high-tunnel systems. Organic fertilizers are commonly applied preplant in organic baby leafy green production. While the nitrogen (N) application rate for growing organic baby leafy greens is yet to be determined in Florida sandy soil conditions, the influence of preplant N rates through organic fertilization on the ASD soil treatment with respect to anaerobic condition development and crop and soil nutrient dynamics as well as crop performance also needs to be evaluated. The objective of this study was to examine different preplant N application rates involved in the ASD treatment in organic high-tunnel and open-field systems for developing recommendations on ASD application in production of direct seeded baby leafy greens. Project findings will contribute to improving ASD as an environmentally-friendly method for weed and nutrient management in organic production. 

Project Objectives:

With the long-term goal of developing cost-effective and environmental-friendly ASD application for improving organic baby leafy green production systems, the specific objectives of this study included:

 

Objective 1: Assess the impact of N application rate on soil cumulative redox potential in ASD-treated soils.

 

Objective 2: Assess the ASD soil treatment impact on soil nutrient dynamics in high-tunnel and open-field systems. 

 

Objective 3: Compare different N application rates for baby leafy green production under ASD treatment in high-tunnel and open-field systems.

Research

Materials and methods:

A field trial was conducted during April – May 2021 at the University of Florida Plant Science Research and Education Unit (Citra, FL). A split-plot design was used, with production system (high-tunnel vs. open-field) as the whole-plot factor and N application rate as the subplot factor. Chick Magic (CM, 5%N-3%P2O5-2%K2O; Cold Spring Egg Farm, Inc., Palmyra, WI) as the N source was applied at seven rates including 8.1 Mg ha-1, 6.6 Mg ha-1, 5.4 Mg ha-1, 4.1 Mg ha-1, 2.7 Mg ha-1, 1.4 Mg ha-1, and 0 Mg ha-1 for preplant N application during the ASD treatment. Molasses (M) at a rate of 6.9 m3 ha-1 was applied as a labile carbon source. Therefore, soil treatments consisted of Control­0 (no CM, no N), ASD120 (M + 8.1 Mg ha-1), ASD100 (M + 6.6 Mg ha-1), ASD80 (M + 5.4 Mg ha-1), ASD60 (M + 4.1 Mg ha-1), ASD40 (M + 2.7 Mg ha-1), ASD40 (M + 2.7 Mg ha-1), ASD20 (M + 1.4 Mg ha-1), ASD0 (M only). ‘Red Salad Bowl’ lettuce (Johnny’s Selected Seeds, Winslow, ME) was direct seeded following the ASD treatment period.

After application of CM and M, soil was tilled with a rotary cultivator, and beds were covered with a 1 mil black/white VaporSafe1 TIF (Raven Industries Inc., Sioux Falls, SD). Using overhead sprinkler irrigation, ASD plots were irrigated for 5 h at a rate of 5 cm of water to saturate air-filled pore space in the top 10 cm of the bed for enhancing the development of anaerobic conditions. ASD treatment period was maintained for 21 days before tarp was removed.

Following the protocol outlined by Paudel et al. (2018), oxidation–reduction potential sensors (PT combination electrodes, Ag/AgCl reference, Sensorex, Garden Grove, CA) were installed to a depth of 15 cm in each plot to measure the redox potential, and thus, to evaluate the level of anaerobiosis achieved in the soil during the first 3 weeks after treatment application. Using a soil probe (1.75 cm internal diameter), three soil cores were taken randomly to a depth of 15 cm from each plot prior to ASD treatment application and at 1, 7, 14, and 21 days after treatment application (DATA). Baseline soil samples were analyzed to determine soil pH and concentrations of NO3-N. Soil temperature and volumetric water content were continuously monitored during the ASD treatment period. Soil temperature/moisture sensors (CS655, Campbell Scientific, Logan, UT) were installed to a depth of 15 cm in each plot before initial irrigation.

During the ASD treatment period, anion exchange membranes (AEMs; Ionics AR204E, Suez WTS Solutions USA, Inc., Minnetonka, MN) were used to measure soil NO3-N flux following procedures by Castro and Whalen (2016). Anion exchange membranes (2.5 cm × 10 cm) were placed in each subplot, vertically oriented 0-10 cm below the soil surface, and they were retrieved and replaced when soil samples were taken. Weed assessment was conducted at 7 and 23 days after sowing (DAS) using 0.25 m2 sampling quadrats and included weed coverage (%) and number of nutsedge per m2.

Total fresh weight of baby lettuce per plot and biometric assessments were taken at harvest. Aboveground biomass was dried at 65˚C until constant weight to measure dry matter content. Dried samples were ground and analyzed for nutrient concentrations of macro- and micronutrients. Sampling quadrats (0.25 m2) were used to determine specific leaf area (SLA, mm2 mg-1 dry weight) and specific leaf weight (SLW, mg dry weight mm-2) in each plot at harvest. Roots were also harvested from 0.25 m2 quadrats for measuring root dry biomass and nutrient concentrations. Leaf color was analyzed one day prior to harvest using the CR-400 Chroma Meter (Konica Minolta Sensing Americas, NJ). Similarly, SPAD values were taken one day prior to harvest using SPAD 502 Chlorophyll Meter (Spectrum Technologies, Aurora, IL).

Research results and discussion:

Data were analyzed using a generalized linear mixed model in SAS Version 9.4 (SAS Institute, Cary, NC). Production system, soil treatment, and their interaction were considered as the fixed effects, while block and the block by production system interaction were considered as the random effects. Fisher’s Least Significant Difference (LSD) test was used for multiple comparisons.

 

Objective 1: Assess the impact of N application rate on soil cumulative redox potential in ASD treated soils.

 

A two-way interaction of production system and soil treatment (p<0.01) significantly affected cumulative soil redox potential (CEh, mV hr). In the high-tunnel system, ASD40, ASD60­, and ASD80 achieved CEh values comparable to ASD100, while ASD20, ASD0, and Control0 significantly reduced CEh values compared with ASD100. A similar trend was evident in the open-field system, where no significant differences in CEh values were observed between ASD40, ASD80, ASD100, and ASD120­. When averaged across soil treatments, CEh levels in open-field systems were higher compared with high-tunnel systems. When averaged across production systems, the main effect of soil treatment revealed significant differences between ASD soil treatments and the controls. Specifically, ASD40, ASD60, and ASD80 did not significantly reduce CEh levels compared with ASD100­. Furthermore, ASD120 did not result in a significant increase in CEh compared with ASD100. Compared to previous studies by Di Gioia et al. (2016) and Guo et al. (2018) which reported CEh levels exceeding 75000 mV hr­ in open-field environments for conventional tomato production, levels of CEh achieved in the current study were lower with the highest level less than 40000 mv hr. On the other hand, the CEh achieved in the current study are similar to those reported by Paudel et al. (2018) for open-field tomato production in Florida using 6.9 m3 ha−1 of molasses and 11 Mg ha−1 of composted poultry litter. Raised beds as commonly employed in tomato production were not used in this baby lettuce study which might have allowed lateral movement of soil water, thereby limiting anaerobic soil conditions. In addition, to mimic farmer production practices for growing leafy greens, overhead irrigation was used prior to tarping. This represents a deviation from the ASD method applied in tomato production using drip irrigation after tarping.

 

Objective 2: Assess the ASD soil treatment impact on soil nutrient dynamics in high-tunnel and open-field systems. 

 

The interaction of production system and soil treatment significantly affected soil NO3-N flux at 1 DATA. In high-tunnel systems, ASD100 and ASD60 resulted in significantly greater soil NO­3-N flux compared with all other treatments. Conversely, significantly lower soil NO­­3-N flux in high-tunnel systems was observed under Control0, ASD40, and ­ASD0 compared with all other treatments. In open-field systems, the greatest level of NO3-N flux was observed under ASD120, while the lowest was observed under ASD40, ASD0, and Control0 treatments. While the results were not significantly different, within each treatment (except for ASD100) a greater level of soil NO­3-N flux was observed in high-tunnel systems compared with their respective open-field treatment. For ASD100, a significantly greater level of soil NO3-N flux was detected in high-tunnel systems compared with open-field.

 

At the end of the 21-day ASD period, production system and soil treatment significantly impacted soil NO3-N flux, although their interaction was insignificant. Compared to the open-field system, soil NO3-N flux was increased by 84% in high-tunnels. When averaged across production systems, significantly greater soil NO3-N flux was detected in ASD100 and ASD120 treatments compared with all other treatments, though no significant differences were observed between Control0, ASD0, ASD20, ASD40, ASD60, and ASD80.

 

When averaged across sampling dates during the ASD period, the main effect of production system significantly impacted soil NO3-N concentrations. High-tunnel systems resulted in a 38% increase compared with open-field systems. These findings suggest that the total crop N requirements for baby leafy greens may be applied during the ASD treatment period without reducing the availability of NO3-N following the ASD treatment period, particularly in high-tunnel systems. Furthermore, high-tunnels may be a suitable production system for implementation of ASD soil treatment in terms of improving N availability and minimizing NO3-N losses.

 

Objective 3: Compare different N application rates for baby leafy green production under ASD treatment in high-tunnel and open-field systems.

 

Production system and soil treatment significantly impacted total fresh weight and dry weight of baby lettuce. No significant effects of production system or soil treatment were evident on leaf dry matter content. High-tunnel systems increased total fresh weight by three-fold compared with open-field systems. No significant differences were observed in terms of harvested fresh weight between ASD40, ASD60, ASD80, ASD100, and ASD120, while fresh weight under ASD20, ASD0 and Control0 treatments were significantly reduced. A similar trend was observed for total dry weight, where no significant differences in dry weight were observed between ASD40, ASD60, ASD80, ASD100, and ASD120, while dry weight under ASD20, ASD0 and Control0 treatments were significantly reduced.

 

At 7 DAS production system and soil treatment significantly impacted weed coverage. High-tunnels resulted in a 40% reduction in weed coverage compared with open-field systems. ASD0 significantly increased weed coverage compared with ASD120, and ASD80. The lowest weed coverage was observed in ASD60. No significant differences were observed between Control­0, ASD20, ASD40, and ASD100. Production system and soil treatment did not significantly affect the number of nutsedge at 7 DAS. At 23 DAS production system and soil treatment also significantly impacted weed coverage. High-tunnels reduced weed coverage by 50% compared with open-field systems. The greatest weed coverage was observed in ASD0, while the lowest weed coverage was observed in ASD60. No significant differences were observed between ASD100, ASD20, Control0, ASD40, and ASD120, while the lowest weed coverage was observed in ASD60.

 

One day prior to crop harvest, SPAD values were significantly affected by production system, and greater SPAD values were observed in high-tunnels compared with open-field production. No significant differences in SPAD values were observed between soil treatments. However, the measurement of leaf color attributes showed that open-field systems exhibited a significantly greater a* value compared with high-tunnel systems. Furthermore, the main effect of soil treatment was evident as ASD0 and Control0 treatments exhibited higher a* values indicating redder leaves. Specific leaf area and SLW are two inversely-related ratios which can be used as an indication of biomass partitioning in plants. A higher SLA value indicates a leaf with a larger surface area per unit biomass, whereas a higher SLW value indicates a thicker leaf per unit area. Production systems significantly impacted both SLA and SLW. Greater SLA was observed in high-tunnel systems compared with open-field systems. Conversely, lower SLW values were observed in high-tunnel systems compared with open-field systems. The concentrations of K and Mg in lettuce leaves were 26% and 42% higher, respectively, in high-tunnel systems compared with open-field systems. Overall, results from this study indicate that production system and ASD soil treatment involving organic fertilization with different N application rates prior to seeding baby lettuce impacted the development of soil anaerobic conditions, nutrient availability, and the production of organically-grown baby lettuce.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

We will present our research findings at the American Society for Horticultural Science 2022 Annual Conference. We also plan to prepare a research manuscript for publication in a peer-reviewed scientific journal. In addition, we plan to host a field day this Fall for project dissemination to demonstrate the application of ASD in high-tunnel production systems for organic salad green production.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.