Improving Soil Health and Cropping Systems Sustainability through Cover Crops: An Integrated Research, Education, and Support Approach

1. Research fields were originally set up in 2020, on two farmer fields, using a randomized complete block design with two levels of cover crops; cover crop vs no cover crop. The first field, belonging to one of the farmer collaborators, Mr. Jamie Weaver, is a 242-ha farm (1.5 ha of which will be used for this study) in Coffee County, TN. The soil is classified by the USDA as Captina silt loam (Fine-silty, siliceous, active, mesic, Typic Fragiudult). This farm has been under 22 years of no-till management with various cover crops. The cash crops grown on this farm have been in a corn (Zea mays)/soybean (Glycine max [L.] Merr.) rotation over the last 22 years. The second field, which belongs to another farmer collaborator, Mr. Will Hutchinson is an 81-ha farm (1.5 ha of which will be used for this study) in Rutherford County, TN. The soil on this farm is classified by the USDA as Dickson silt loam (Fine-silty, siliceous, semiactive, thermic Glossic Fragiudult). This field was under a corn/soybean rotation during 2017-2020 and a corn monoculture during 2021 – 2022, and soybean during the 2023 planting season. For this study, it will be maintained under continuous corn. Further, Mr. Hutchinson’s farm has been under no-till management since 2018 when cover crops were first introduced.

The cover crops of choice during the first year of this project will be a mixture of cereal rye (Secale cereal L.), crimson clover (Trifolium pretense L.), hairy vetch (Vicia villosa L.), triticale (Triticale hexaploide Lart.), and oats (Avena sativa). Thesecover crops were selected in consultation with the collaborating farmers because of their hardiness, adaptability to various climatic conditions, ease of management, biomass production, and popularity among producers (based on the last national survey of cover crops; SARE 2020). They also provide other ecological benefits such as atmospheric nitrogen fixation, weed suppression, and soil conditioning. Subsequent cover crops will be determined using the Universities of Tennessee and Kentucky recommendations for the region and the interactive Southern Cover Crop Council’s resource guide (https:/ southerncovercrops.org/cover-crop-resource-guide/row-crops/) to help match the producer’s goals with the most appropriate cover crop species. These cover crops will be planted in the fall after the harvest of the cash crop and terminated in spring. They will be terminated using a roller crimper. The cash crops that will be grown for the duration of the proposed project will be corn and soybean, with a corn/soybean rotation on Mr. Weaver’s farm and continuous corn on Mr. Hutchinson’s farm. The soil will also be under no-till management throughout the study. For this study, a randomized block design will be used with 3 replicates of cover crops and 3 replicates of no cover crops. Each plot (on both farms) will measure 20.1 m in length and 7.4 m in width (with a 3 m wide buffer between each plot).

In situ saturated hydraulic conductivity will be measured using a Guelph permeameter, A Spectrum WaterScout SM 100 sensor and Watchdog 1400 irrigation station will be used to continuously measure in-situ water content and temperature at 0-10, 10-20, and 20-30 cm depths in each plot. Watermark^® sensors (based on electrical resistance of the soil) will be used to measure in situ soil water potential. The sensors will be buried at the aforementioned soil depths. These sensors will be connected, wirelessly, to a cloud-based web service (SensMit^® Web) to allow real-time access to the field data. Thermal property sensors (TP01) and heat flux probes (HFP01) (Hukseflux Thermal Sensors BV) will be used to make continuous measurements of soil thermal conductivity and heat capacity, respectively, at 0-10, 10-20, and 20-30 cm depths. These sensors and probes will be connected to dataloggers that will enable researchers to make continuous measurements at various depths for the duration of this project. Ambient temperature, humidity and precipitation will be measured using automated weather stations (Campbell Scientific).

Exploratory data analysis will be used to identify general patterns in the data. Additionally, analysis of variance will be conducted on soil property data using the general linear model procedure in SAS. Single degree of freedom contrasts will be divided into ‘cover crop vs. no cover crop’. Analysis of variance will also be conducted to determine the effects of cover crops on in situ measured soil properties. Dr. Samuel Haruna (PI) and Mr. Will Hutchinson (farmer) will be involved in sensor installation with help from undergraduate students. Mr. Hutchinson will benefit from improved understanding of the philosophy and role of sensors and their integration in agriculture for improved cropping systems resilience.

A potential challenge for this objective is weather variability which might delay cover crop planting, soil sampling and sensor installation. However, this will provide important information on best management practices to combat this challenge in the region. This will be included in the education and outreach report that will be generated from this study.  

2. Cover crops can influence the various soil health parameters and the subsequent cash crop growth because of their above- and belowground biomass (Haruna et al., 2020). To fully understand the contributions of cover crops, soil samples were collected during the fall of 2020 (before cover crop planting) to evaluate the antecedent soil properties (e.g., SOC, pH, bulk density, soil N, and microbial biomass) and the spatial variability of these properties on both fields. Soil samples will be collected using cylindrical cores (volume = 147 cm³) from each plot at 0-10, 10-20, and 20-30 cm depths. These depths were chosen because most of the roots of our chosen cover crops are concentrated at these depths (Bodner et al., 2019) and therefore, we expect the influences of cover crops to be more prominent at these depths. These soil samples will be collected each spring (beginning during spring 2025) just before the cover crops are terminated for the evaluation of the influence of cover crops on soil health parameters.

Saturated hydraulic conductivity will be measured using a constant head permeameter already available in the soil science laboratory at MTSU) using the methods of Reynolds and Elrick (2002). Water retention will be analyzed using the methods of Dane and Hopmans (2002). The core method (Grossman and Reinsch, 2002) will be used to analyze soil bulk density. Water infiltration will be analyzed using double ring infiltrometers already available as part of Dr. Samuel Haruna’s (PI) soil science laboratory at MTSU. Soil pH will be analyzed by potentiometry using an electronic pH meter. Soil organic carbon and nitrogen will be measured using the combustion method in a Skalar Primacs^SNC-100 (Skalar Analytical B.V., The Netherlands) already available in the soil science laboratory at MTSU.  

Soil microbial community and activity is an important aspect of crop production (e.g., rhizobacteria can trigger in fixation of atmospheric nitrogen into the soil through a symbiotic relationship with legumes) and greenhouse gas emission (because of their metabolic activity). Thus, this objective will synthesize data from the first objective and measured microbial activity to determine the role of cover crops and soil thermal properties on greenhouse gas emissions. Another set of samples will be collected using a soil auger at the aforementioned soil depths for aggregate stability and microbial community structure. Soil microbial community structure will be determined on samples collected from the research plots using phospholipid fatty acid analysis (PLFA) (Quideau et al., 2016). This method will enable researchers to estimate total microbial biomass and observe broadchanges in soil microbiota composition. Available software can automatically name the PLFAs in a sample, categorize them by microbial origin and perform biomass calculations and ratios. Dr. Seockmo Ku’s (Collaborator at Texas A&M) previous research has shown promising results in reducing the time required for microbial enrichment and detection (Ku et al., 2016). His participation in this research will lead to the development of quality research materials on microbial analysis with long shelf-life. Dr. Ku’s expertise in microbial detection and isolation from various media will be a valuable resource when identifying and analyzing soil microbial communities in this project.

A portable gas analyzer, Gasmet ® DX4040, will be used to measure greenhouse gas emissions. This analyzer uses Fourier Transform Infrared (FTIR) spectroscopy to measure the concentration of greenhouse gases emitted from soils. This analyzer is already present at MTSU and has been used for various studies on greenhouse gas emissions by Dr. Song Cui (Co-PI). Greenhouse gases of interest include methane (CH₄), carbon
dioxide (CO₂) and nitrous oxide (N₂O). Plant height, chlorophyll content, and biomass will be measured at different stages of crop growth to improve understanding of the effects of cover crops on the development of the subsequent cash crop. Chlorophyll content will be measured weekly (after emergence) using a Soil Plant Analysis Development (SPAD-502Plus) meter (Konica Minolta®). Grain yield will be measured using crop-cut methods.

Drs. Samuel Haruna (PI) and Song Cui (Agronomist, Co-PI) will lead this effort with help from Mr. Jamie Weaver (farmer collaborator). This objective will also enable researchers determine the link between cover crops, soil thermal properties, greenhouse gases, and the yield of the subsequent cash crop.

Due to his interest in soil health, Mr. Weaver will benefit from improved knowledge on how cover crops can improve cropping system sustainability by improving soil health indicators. Further, results will be disseminated through seminars and workshops in Tennessee (to be led by Dr. Chaney Mosley, Co-PI, with help from local farmers: Mr. Jamie Weaver and Mr. Will Hutchinson), and Kentucky (to be led by Drs. Edwin Ritchey and John Grove, Co-PI, with help from local farmers including Mr. Joel Reddick).

A potential challenge to this objective is that 3 years may not be enough to detect significant effect of cover crops on soil health parameters. However, by leveraging an existing research established in 2020, we believe that significant effects will be noticed during 2025 and 2026 (effectively, 5 to 6 years after establishment).

3. Using the soil health data and plant growth parameters obtained from objectives 1 and 2, the interdependence between soil health indicators, crop growth and productivity, environmental sustainability, insect damage and disease incidence, and the financial viability of current cropping systems will be analyzed. We will use visual (Bock et al., 2020) and smartphone based applications (e.g., You Only Look Once, YOLO v4; Chen et al., 2021) to detect and score disease incidence and pest damage in the field. A partial budget analysis will be used to determine the financial viability of cover crops and demonstrate the economic value of providing a no-till seed drill to underserved farmers. Also, we propose to extrapolate local soil quality and economic results regionally by accessing the USDA’s Agricultural Resource Management System (ARMS). Analysis of variance will be conducted on soil health indicators, microbial biomass, and greenhouse gas data using the general linear model procedure in SAS for both single degree contrasts and interaction effects. Further, we will use principal component analysis and simple machine learning algorithms to evaluate and understand the complex data that will be generated. Researchers will seek to develop guidelines for successful cover crop integration into current cropping systems for greenhouse gas mitigation. Results will be published in scientific journals online. Drs. Justin Gardner (Agricultural Economist, Co-PI) and Samuel Haruna (PI) will lead this objective with help from undergraduate students and other collaborators. We will leverage Dr. Song Cui’s (Co-PI) machine learning expertise in analyzing these complex data and relationships.
   
   
4. A no-till seed drill will be purchased and made available for use by lower income and minority farmers, at no cost to them to encourage the adoption of cover crops. The cost of this seed drill and transportation is built into the budget for the current project.

Building on the results of the previous objectives, we will determine the profitability of using cover crops in crop production systems in the southern US. From the yield analysis data, we will evaluate the economic viability of using cover crops on corn profitability. This information will enable educators to instruct farmers and citizens on using cover crops to improve crop productivity and enhance the resilience of their cropping systems. Furthermore, we will develop a strong outreach program between the participating universities, farmers, and local NRCS offices. We will disseminate results through in-person and hybrid events such as seminars, workshops, and field days in Tennessee (to be led by Dr. Chaney Mosley), and Kentucky (led by Drs. Edwin Ritchey and John Grove, and Mr. Joel Reddick [farmer]). First year workshops will include farmer survey on reasons for including or not including cover crop in their management practices. This will help investigators incorporate farmer opinion in final recommendations. Field days will facilitate the education of citizens and high school students. Further, we will create research briefs to summarize and highlight research results in a way that is easy for the public to understand. These briefs will be hosted on MTSU and University of Kentucky websites and in extension offices. This will guarantee long shelf-life for these resources. Further, research results will be developed into lesson plans with laboratory activities for agriculture teachers. Social media sources (Twitter, Facebook, YouTube® shorts, etc.) will be used to further disseminate results.

Additionally, we will also host high school agriculture teachers for several hours during the Annual Agriculture Teachers Conference. During these meetings, a survey will be conducted on ways to improve student engagement in sustainable agriculture. Results will be developed into lesson plans with laboratory activities for agriculture teachers. This resource will be made available on institutional websites. Public engagement with these resources can be tracked through the number of clicks and downloads.

An external evaluator (Dr. Ying Jin, James Madison University) will play a critical role during the life of the project. Dr. Jin has previous experience evaluating various projects at local, regional, and national levels. The evaluator will meet with researchers, educators, and farmers during the first year of the project to evaluate the agronomic (planting, harvesting) plan, sensor installation plan, soil sample collection method, and workshop/seminar survey plan. During the second and third years (2025 and 2026), the evaluator will meet with researchers, educators, and producers to evaluate project activities from the previous year. Furthermore, during the second-year evaluation, the evaluator will provide suggestions on how to improve the project during the third year. At least 1000 citizens are projected to benefit from the education efforts across the Southeast region.