Organic spinach is among the top organic vegetables sold in the United States, and growth of spinach production tops the list. Climatic conditions have limited spinach production in the southeastern U.S., where high humidity and warm temperatures negatively affect spinach growth and quality. Florida’s climate also includes drastic variations in temperatures during the spinach growing season. High tunnel system and appropriate cultivar selection has the potential to mitigate many of these environmental extremes, yet there is a lack of research-based information on organic spinach production under Florida conditions. Additionally, compost application may help overcome spinach germination difficulties, which is a challenge to growers particularly in warm climates. Given the growing interest in spinach production in Florida, the objectives of this project are to (1) identify the current spinach production practices of organic farmers and challenges of organic spinach production in Florida to understand the range of issues and most common difficulties faced; (2) assess the effects of cultivar, compost, and high tunnel system on organic spinach production to develop techniques which help mitigate identified common difficulties; and (3) disseminate research information through a growers’ workshop and presentation at the Florida State Horticultural Society conference. This research will address the SARE targeted issues by (1) identifying production methods and systems that help overcome production challenges, improve environmental quality, and promote crop diversity, (2) developing cultivar and compost management recommendations towards improving organic farming methods for growers in the South, and (3) improving quality of life of local growers and consumers by enhancing production of spinach, a widely consumed health-promoting, nutrient-dense leafy vegetable.
The goal of this research is to identify production techniques that promote sustainable spinach production in Florida.
Objective 1: Identify the current spinach production practices of organic farmers and challenges of organic spinach production in Florida to understand the range of issues and most common difficulties faced.
Objective 2: Assess the effects of cultivar, compost, and high tunnel system on organic spinach production to develop techniques which help mitigate identified common difficulties.
Objective 3: Disseminate research information through a growers’ workshop and presentation at the Florida State Horticultural Society conference.
A preliminary, 2017-2018 winter trial was conducted at the Plant Science Research and Education Unit (PSREU) in Citra, FL, to build on previous spinach research at the University of Florida. A split-split plot design was utilized, with the production system (high tunnel and open field) as the whole plot factor, compost application method (tilled and furrowed) as the subplot factor, and compost type (plant based and cow manure based) and rate (0, 10, and 20 tons per acre) as the sub-subplot factor. Soil samples were taken at planting to explore treatment effects on physical, chemical, and biological soil quality indicators. Germination data was captured via the Canopeo App (www.canopeoapp.com), which calculates the amount of green in a picture frame. Harvest units were established by thinning plants to 3 inch spacing in order to eliminate germination effects and assess plant growth rates on a per plant basis. Spinach was harvested 50 days after seeding for fresh weight, dry weight, and nutrient analysis. A high tunnel 2018 spring trial assessed compost treatments in organic spinach production in another high tunnel location at PSREU. A split plot design was used, with the seeder type (Earthway and Jang) as the whole plot factor and compost application method (tilled and furrowed) in combination with rate (0, 10, and 20 tons per acre) as the subplot factor.
In order to fulfill a substantial internship requirement for the Doctor of Plant Medicine program, the graduate student is currently working part time at a high tunnel, baby leafy greens farm in North Florida (from October 2018 until the present). It has enabled the graduate student to understand large-scale baby spinach production systems, detect some of the constraints in both conventional and organic spinach production in Florida sandy soils, and identify potential applications for the research conducted within this SARE grant.
One of the principal constraints in organic spinach production on sandy soils in Florida is the presence of soil-borne seedling diseases that cause damping off. This occurred during the small-scale trials at University of Florida/IFAS Plant Science Research and Education Unit and at the commercial farm, and multiple times the incidence has been so great it has caused complete crop failures. A small, organic observational trial was conducted in January 2019 at the high tunnel commercial farm in which compost was applied to 6-ft sections on top of raised beds at 1-inch and 2-inch depths. A soil sanitizing product was used on two beds within the same tunnel. Multiple microbial products were also used in adjacent, organically certified high tunnels (as well as in multiple lots throughout the production season). Spinach seeds were drilled directly into the compost, as well as into the sanitized and microbially amended treatments and the unamended control.
A large-scale, replicated organic trial will begin in mid-April. Treatments will consist of the soil sanitizer, the control, and compost spread at a 1-inch depth. Half of the compost will be tilled in and beds will be reformed, while half will remain on top of the raised beds. Each treatment will be in one of four beds per tunnel, at 5 ft wide by 100 ft long, with 3 replications. From previous trials, the expected outcome is that the spinach drilled into compost will be isolated from the soil pathogens at the early stages of growth and will therefore only be minimally affected, producing a harvestable crop, while the other treatments will not prevent damping off by the soil-borne pathogens. The compost we will be using is a plant-based compost that has demonstrated effectiveness in observational trials, while having lower pH, EC, and C:N ratio compared to the manure-based compost previously used. Additionally, it is also by far the most economical compost identified in Florida at half the price of the previously used compost. A rate of 80 tons per acre is needed to reach the desired depth of 1 inch.
Additionally, another large-scale, replicated trial will also begin in mid-April. This will be in a section of the farm in which the soil is very coarse and drains rapidly, and in which, over two years, a profitable spinach crop has yet to be grown. In this trial the purpose is therefore to examine how treatments will affect nutrient and water holding capacity, in addition to overall crop performance. Treatments will consist of compost added to 1-inch depths on bed tops, as well as 1-inch of compost added and tilled, and an unamended control. Additionally, there will be a polymer and polyacrylamide product used as a fourth treatment, which claims to improve water holding capacity of the soil, though obviously will not provide other chemical, physical, and biological benefits of compost additions. Soil moisture content, plant available water, saturated hydraulic conductivity, and bulk density will again be measured, as well as crop response to the different treatments. While this is a conventional trial, this is being included as part of this project in order to understand soil moisture dynamics of the compost treatments at the field level. Not enough soil moisture probes are available to use for both trials, and this conventional trial will meet the needs of the commercial farm, while quantifying critical soil moisture parameters affected by the different compost treatments in the organic trial.
Results from the 2017-2018 winter trial showed lower bulk density, higher CEC and nutrient content, and higher total carbon and organic matter in furrowed treatments than tilled treatments, and no significant differences between tilled treatments and the control. In tilled treatments, a slight increase in plant available water (7.1%) and decrease in bulk density (8.3%) was measured at 20 tons per acre compost rates compared with the unamended control in tilled treatments, while no difference was found at compost rates of 10 tons per acre compared with the control. Interestingly, saturated hydraulic conductivity of soil was 65% greater in the 10-ton tilled treatment and 318% greater in the 20-ton tilled treatment compared with the unamended control. Untilled compost treatments at 20 tons per acre, however, increased plant available water by 600%, decreased bulk density by 70%, and increased saturated hydraulic conductivity by more than 5000% in the top 2 inches (the compost horizon).
Results from the 2017-2018 winter and 2018 spring trials demonstrated significant germination increases with increasing amount of compost additions in the furrowed treatment, while the tilled treatment was not significantly greater than the control. Additionally, the 2017-2018 winter trial illustrated germination was greater in the cow manure based compost than the plant based compost, most likely due to the poorer quality (larger particle size) of plant based compost received. Fresh weight revealed no significant differences in growth rates between compost treatments, while high tunnel yields were 174% greater than the open field, due to an increase in both leaf number per plant and leaf size.
In the January 2019 observation trial, the increase in spinach crop stand was captured via the Canopeo App, and the averaged compost treatments had 2.0 to 17.5 times the crop stand of the other treatments, with an average of 4.1 times the crop stand of the other treatments. The compost treatments had consistent results, while all other treatments had very high variability. After two and a half cycles of continuous plantings (alternating spinach and arugula in each location, while planting in seven different blocks per cycle and one block per week), the microbial treatments have not improved the crop stand compared with the unamended control. The performance has been so poor that half of the 16 plantings have been terminated prior to harvest.
Educational & Outreach Activities
In spring of 2018, the graduate student visited six spinach growers from north, central, and south Florida and corresponded with a few others. Interestingly, there are numerous conventional spinach growers who are only limited by the subtropical heat of Florida’s summers. For organic growers, spinach cultivation is so difficult that the majority do not even attempt to grow it. Poor germination and/or lack of crop stand are the common reasons organic growers keep spinach as a periphery crop. A grower survey is now being developed to further explore these obstacles with a wider audience of growers to identify opportunities for research to alleviate these production challenges and increase organic spinach production in Florida.
Preliminary results from the winter trial were presented at the Southern Region – American Society of Horticultural Sciences in Jacksonville, FL.