Regenerative Agriculture: Effects of Cover Crop and Mycorrhizal Inoculation on Salt Stress Mitigation in Floridian Tomato Cultivars

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Commodities

• Vegetables: tomatoes

Practices

• Crop Production: cover crops, crop improvement and selection

The objective of this comprehensive investigation is to assess and validate the effectiveness of two regenerative agriculture (RA) methods-specifically, the implementation of a pigeon pea cover crop-green manure and the inoculation with the mycorrhizal species Glomus intraradices-in mitigating the effects of salt stress on two distinct tomato cultivars, Solanum lycopersicum cv. Tasti-Lee and Solanum lycopersicum cv. Sanibel. The rationale behind this research is rooted in the pressing need to address the escalating challenges posed by soil salinity in Florida, a critical concern for tomato production.

As tomatoes represent a cornerstone of Florida's agricultural economy, it is imperative to develop sustainable solutions that can fortify the resilience of tomato crops against the burgeoning threats of saline stress. The chosen cultivars, Tasti-Lee and Sanibel, provide an intriguing comparative platform. Tasti-Lee, renowned for its adaptability to Floridian conditions, is anticipated to exhibit robust vigor in the face of saline challenges. On the other hand, the relatively understudied Sanibel variety presents an intriguing prospect, as its response to salt stress is not well-documented. It is plausible that Sanibel may manifest comparable or even superior growth and yield results under saline conditions.

The innovative aspect of this proposed solution lies in the combined treatment strategy, leveraging both the pigeon pea cover crop-green manure and mycorrhizal inoculation. We hypothesize that this synergistic approach will yield the most substantial positive impacts on the growth and crop yield of both Tasti-Lee and Sanibel cultivars when subjected to salt stress. If our hypothesis proves correct, this dual application of regenerative agricultural practices would emerge as a potent and cost-effective resource for farmers and gardeners, regardless of the scale of their operations, who grapple with salinity challenges in their fields.

The primary focus of our investigation is to provide empirical evidence supporting the efficacy of these RA methods as sustainable and practical solutions for salt-stressed tomato cultivation. The experiment will be conducted under controlled conditions, systematically manipulating saltwater stress levels, and meticulously monitoring the response of each cultivar to the designated treatments. The outcomes of this research hold the promise of not only enhancing the salt tolerance of tomatoes but also contributing valuable insights that can be extrapolated to other crops facing similar challenges in saline-prone regions.

The first RA method under scrutiny involves the incorporation of a pigeon pea cover crop, which will serve a dual purpose as both a cover crop and green manure. Pigeon pea cover crops have demonstrated efficacy in weed control, nutrient retention, and soil moisture conservation (Benedict et al., 2014; Sharma et al., 2018). As a green manure, the cover crop can be plowed into the soil, enriching it with organic material and enhancing nutrient availability (Finney et al., 2017). By investigating the impact of pigeon pea cover crop-green manure on the two tomato cultivars, we aim to elucidate its potential role in ameliorating salt stress and improving overall crop health and productivity.

The second RA method involves the introduction of the mycorrhizal species Glomus intraradices to the tomato root system. Arbuscular mycorrhizal fungi (AMF) have been acknowledged for their positive influence on plant health and performance under stress conditions (Ruiz-Lozano et al., 2012; Selvakumar et al., 2014). AMF form symbiotic relationships with plant roots, enhancing mineral acquisition and aiding in the regulation of ion osmotic potential. By exploring the impact of G. intraradices on the two tomato cultivars, we seek to unravel the potential of mycorrhizal inoculation as a targeted strategy for mitigating salt stress effects, thereby bolstering the resilience of tomatoes to adverse environmental conditions.

The combined application of these RA methods aims to create a holistic and sustainable approach to salt stress mitigation in tomato cultivation. By synergistically leveraging the benefits of cover cropping and mycorrhizal inoculation, we anticipate observing enhanced plant vigor, improved physiological responses, and ultimately increased crop yield under saline conditions. The robustness of this dual strategy lies in its potential to offer a comprehensive solution that addresses multiple facets of salt stress, from soil health to plant physiology.

The significance of this research extends beyond the laboratory, reaching into the practical realm of agriculture. If our hypothesis is substantiated, the proposed RA methods could emerge as accessible and economically viable tools for farmers and gardeners grappling with salinity challenges in their fields. The scalability and cost-effectiveness of these methods make them particularly appealing for both large-scale agricultural enterprises and smaller, community-based initiatives. This aligns with the broader goal of regenerative agriculture, which emphasizes sustainable practices that not only enhance productivity but also contribute to the long-term health and resilience of agricultural ecosystems.

This research endeavors to contribute substantively to the ongoing efforts to address the escalating challenges of salt stress in Florida's tomato production. By focusing on the Tasti-Lee and Sanibel cultivars and employing a dual RA approach, we aspire to provide empirical evidence that supports the practical implementation of these regenerative agricultural methods. The potential benefits extend beyond the specific tomato cultivars under investigation, with implications for the broader agricultural landscape facing similar challenges. Ultimately, the success of this proposed solution would mark a significant step toward building sustainable and resilient agricultural practices in the face of evolving environmental threats.

Phase 1: Growth Chamber/Lab Component:

The initial phase of this study comprises two critical components: Seed ecophysiology assessment under saline stress and field crop performance under saline stress.

Seed Ecophysiology Assessment:

Seed germination and vigor tests will be conducted using three repetitions of 50 seeds from two tomato cultivars. The seeds will be incubated in petri dishes containing towelettes moistened with 0, 2, 4, and 6‰ NaCl solutions. Germination rates will be recorded at 7 and 14 days, and measurements of emerging hypocotyls and epicotyls will be obtained.

To evaluate stress-related nutrient loss, seeds will undergo incubation with the same salinity treatments for 6 and 24 hours. Following this, the seeds will be washed, submerged in 50 mL distilled water, and the water medium will be tested using nutrient ion sensors for N, P, K, Ca, and Mg concentrations, along with electrical conductivity sensors to assess overall ion loss.

In order to observe stress-related moisture loss, seeds will be subjected to the petri dish method for 6 and 24 hours. Afterward, the seeds will be weighed, dehydrated, and reweighed. The difference in wet and dry weights will reveal seed moistures corresponding to each salinity treatment.

Phase 2: Field Crop Component:

The field crop component involves several key steps:

1. Soil Preparation with Green Manure:

   - Each tomato cultivar group (Tasti-Lee and Sanibel) will undergo initial soil preparation with green manure in 120 pots.

   - Nitrogen-fixing pigeon pea (Cajanus cajan) will be inoculated with Bradyrhizobium sp. (Pro-Mix BX Mycorrhizae, Premier Tech, Pennsylvania, US) and grown for three months before being mulched into the soil.

   - This will result in three soil media treatments: 4 pigeon pea plants per pot, 2 pigeon pea plants per pot, and no pigeon pea plants per pot.

2. Tomato Season Step:

   - Following soil preparation, the tomato season step will commence, with tomato seeds planted for the Fall 2023 season.

3. Salinity Treatments:

   - Within each soil group, four sets of salinity solutions (6‰ NaCl, 4‰ NaCl, 2‰ NaCl, and distilled water) will be applied at five repetitions each.

4. Mycorrhizal Inoculation:

   - Across all soil media and salinity groups, half of the tomatoes will be inoculated with the beneficial mycorrhizal species Glomus intraradices (Pro-Mix BX Mycorrhizae, Premier Tech, Pennsylvania, US); the remaining half will remain uninoculated.

5. Physical Leaf Measurements:

   - Leaf area changes will be measured every two weeks.

   - Histological samples for stomatal morphology will be obtained biweekly.

   - NDVI, SPAD, and atLEAF measurements will be taken for assessing photosynthetic activity and chlorophyll content.

Phase 3: Market and Taste Assessments:

1. Physical Measurements of Fruits:

   - Fruit measurements will include yield per plant, size of fruit, and firmness determined via penetrometer.

2. Chemical Tests of Fruit Samples:

   - DPPH and FRAP assays will be conducted to assess antioxidant content.

   - RP-HPLC and mass spectrometry readings will be performed to quantify sugar, lycopene, and organic acid content.

3. Chemical Testing of Pot Soil:

   - Salinity, electrical conductivity, pH, and N, P, K, and micronutrient readings will be measured every two weeks using laboratory pH meters and manual ionic sensors.

4. Taste Panels:

   - Taste panels with focus groups will be organized through the FIU Biscayne Bay campus’ Hospitality Management program. Tomatoes will be scored based on sour and sweet flavors.