Progress report for OS20-135
This on-farm research project is a response to growers’ interest in seeking innovative solutions to overcome weed and disease management challenges in organic carrot production systems. Anaerobic soil disinfestation (ASD) is an environmentally-friendly disease and weed management technique that has great potential to enhance beneficial soil microbial growth and soil fertility through the addition of organic amendments. However, the cost of implementing ASD treatments in commercial production is often perceived as an economic barrier for the wide-spread adoption among organic growers. To address cost concerns from the grower, we used locally sourced labile carbon amendments and re-usable 6-mil silage tarp, which allows the grower to reduce waste from using single-season plastic covers. By teaching the grower how to implement ASD treatment utilizing locally available resources and re-usable tarp, we expect to establish a partnership with local growers for technology and knowledge transfer which allows for a practical assessment of ASD with respect to its potential for improving high-value vegetable production systems. This on-farm project will also enable us to obtain a practical, up-to-date understanding of the costs associated with ASD application toward optimizing its benefits. Furthermore, major challenges and concerns related to on-farm implementation of ASD practices will be better identified through this researcher-farmer partnership for developing future research dedicated to enhancing crop performance and long-term environmental and economic sustainability of organic farming systems.
The specific objectives of this project include:
Objective 1: Develop ASD treatments based on farmer-recommended inputs that fit within the site-specific farming system.
Objective 2: Determine the effectiveness of ASD for controlling weeds and soilborne diseases in the production of organic, direct-seeded carrots.
Objective 3: Assess marketable yield and carrot quality as affected by ASD treatments.
- - Producer
We collaborated with the Siembra Farm located in Gainesville, FL to carry out all the field trials. Trial 1 was conducted during September 2021-January 2022. The other two ongoing trials were initiated in December 2021 and February 2022, respectively. All the field trials were arranged in a randomized complete block design with three replications. Four soil treatments were included: 1) Grower’s practice (control): Nature Safe organic fertilizer applied at a nitrogen (N) rate of 130 lb/acre, with on-farm compost applied at 7.5 bushels/100 ft2; 2) ASD1: ASD with Nature Safe organic fertilizer applied at 175 lbs N/acre and blackstrap molasses at 741 gal/acre, with on-farm compost applied at 7.5 bushels/100 ft2; 3) ASD2: ASD with Nature Safe organic fertilizer applied at 130 lbs N/acre and blackstrap molasses at 741 gal/acre, with on-farm compost applied at 7.5 bushels/100 ft2; and 4) ASD3: ASD with Nature Safe organic fertilizer applied at 175 lbs N/acre and blackstrap molasses at 741 gal/acre, without on-farm compost. The amendments and organic fertilizer were incorporated into the soil using a rototiller, and 2 acre-inches of irrigation water were applied prior to tarping through overhead irrigation. All the ASD treatments and the control plots were covered by 6-mil silage tarp for three weeks before carrot seeding. Carrots were then directly seeded at 630,000 seeds/acre for all three trials after the three weeks of ASD treatment.
During the ASD treatment period, the level of anaerobicity (CEh) achieved in the ASD treatments and the control plots were monitored using the oxidation-reduction potential probes. Soil samples were also collected to monitor changes in soil pH and concentrations of NH4-N and NO3-N at 0, 1, 7, 14, and 21 DAT (days after treatment). In trial 1, carrot weight and number were measured at harvest to determine total and marketable yields. Depending on the disease pressure, disease incidence and severity and root-knot nematode infestation were assessed during the trial. Weed assessment was also conducted.
Data from trial 1 were analyzed using the GLIMMIX procedure of SAS. Multiple comparisons between treatments were conducted using Fisher’s least significant difference test at the 5% level of significance.
Trial 1 was completed during this reporting period. In general, ASD1 and ASD3, the two treatments with higher application rates of Nature Safe organic fertilizer (175 lbs N/acre) achieved approximately 35% higher CEh levels compared with ASD2 and the control, although the difference was not statistically significant. Compared to previous studies, which reported CEh levels ranging from 50000 to 87894 mV hr using composted poultry litter and molasses in open field tomato production systems in Florida (Di Gioia et al., 2016; Guo et al., 2017), levels of CEh in the current study were lower, ranging from 16285 mV hr in the control to 22960 mV hr in ASD1. In the current study, overhead irrigation instead of drip irrigation was used prior to tarping, which may have limited the development of anaerobic soil conditions.
During the ASD treatment period, soil pH did not differ significantly among soil treatments. At 14 DAT, soil pH was decreased to the lowest level for all treatments in comparison with the other sampling dates. At the end of the ASD treatment period (21 DAT), soil pH tended to recover, reaching a level similar to the original value at 0 DAT. In terms of soil NH4-N and NO3-N concentrations during the ASD treatment period, no significant differences were observed among the soil treatments.
Root-knot nematode infestation was assessed at harvest. Plants were dug up and root galling was evaluated based on a 0-10 scale (0 = no galls and 10 = plant and roots dead). Overall, very few root galls were observed, indicating a rather low level of root-knot nematode infestation in the field. With respect to weed assessment, soil treatments did not differ significantly in weed count, although the number of weeds tended to be lower in the ASD1 plot relative to other treatments during the carrot production season. Spiny sowthistle, American pokeweed, and common lambsquarters were among the major weed species detected.
In trial 1, ASD3 had the highest marketable and total numbers of carrots harvested, while ASD2 led to the lowest number of carrots at harvest. Similar levels of carrot weight yield were observed among different soil treatments, along with similar sizes of carrots. Since the other two trials are still underway, the impact of soil treatment on carrot yield performance will need to be further assessed when data collection for all three trials is completed.
Educational & Outreach Activities
We plan to present our research findings at the American Society for Horticultural Science (ASHS) or Florida State Horticultural Society (FSHS) annual conference next year. We will discuss the project dissemination plan with the grower when all the field trials are completed.