Doctoral Dissertations

Date of Award

12-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

Sindhu Jagadamma

Committee Members

Shawn Hawkins, Song Cui, Debasish Saha, Sindhu Jagadamma

Abstract

The rising demand for organic grains in the southeastern United States presents an excellent opportunity for farmers to transition to organic agriculture. However, this shift brings significant challenges, including the reliance on intensive tillage and organic amendments for nutrient management, weed control, and yield maintenance. Intensive tillage deteriorates soil health, while the timing of nutrient release from organic inputs often lags behind crop demand. Furthermore, the lack of clarity and consistency in the terminology surrounding ecologically-focused agricultural systems hinder market demand from consumers and adoptability by farmers. This study developed a conceptual framework to clearly differentiate these systems. In addition, key challenges in transitioning to organic grain production were evaluated, specifically productivity, weed management, nitrogen dynamics, and soil health. The field experiment was initiated in 2020 on certified organic land at the University of Tennessee's East Tennessee Research and Education Center in Knoxville, TN. The study employed a full-entry study design and established a three-year rotation of soybean, wheat-soybean double-crop, and corn and tested four cropping systems treatments that incorporate different tillage intensities, cover crops, and organic fertilization. These treatments are: (i) highly tilled system (HTS), (ii) moderate-tilled system (MTS), (iii) least-tilled system (LTS), and (iv) low-input system (LIS). We hypothesized that reduced tillage systems, combined with cover crops and organic amendments (MTS and LTS), would enhance soil health, optimize nitrogen-use efficiency, and sustain yields compared to HTS and LIS. Results demonstrated that MTS and LTS exhibited the greatest improvement in soil carbon accumulation and soil health while maintaining comparable yields and weed suppression to HTS. Notably, LTS showed comparable yields and soil organic carbon to fertilized treatments but poor cover crop biomass and soil health. Mineralization metrics such as potentially mineralizable nitrogen and microbial respiration assays, alongside the quality and quantity of total carbon and nitrogen inputs, were identified as effective predictors for optimizing nitrogen use efficiency and synchronizing nutrient release with crop demand. This research underscores the potential of integrating conservation practices such as reduced tillage, cover cropping, and precise nitrogen management, to enhance both agronomic performance and environmental sustainability in organic grain systems in the Southeastern U.S.

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