Doctoral Dissertations

Orcid ID

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Plant, Soil and Environmental Sciences

Major Professor

Xinhua Yin

Committee Members

Virginia Sykes, Sindhu Jagadamma, Jaehoon Lee


The use of agronomic conservation practices can enhance soil C and N sequestration via mitigating C and N emissions. However, the long-term influences of bio-covers, crop sequences, and phosphorus (P) fertilization on aggregate-associated soil organic C (SOC) and N and C-equivalent emissions are largely unknown in no-tillage systems. The objectives of this research were to determine soil aggregate-associated C and N status and C footprint, net C gain, and sustainability index under crop sequences of corn, soybean, and cotton interacted with bio-covers of poultry litter, hairy vetch, winter wheat, and fallow, which represent the major cropping systems in the Mid-south; and examine the effects of P application rates (0, 29, 59, 88, and 117 kg P ha-1) on SOC and N on field with low to medium P fertility levels under corn-wheat-soybean systems. The long-term bio-cover and crop sequence experiments (2002-2017) and P fertilization trials (2009-2018) at Milan and Springfield, Tennessee under no-tillage were used for this research. Poultry litter resulted in higher SOC and N concentrations in microaggregates (0.053–0.25 mm) at 0-5 cm than hairy vetch, wheat, and fallow. Crop sequences involving corn (continuous corn, corn-soybean, and cotton-corn) caused higher SOC levels in microaggregates at 0-5 cm than the other sequences. Annual application of 88 kg P ha-1 accumulated higher SOC and N than 0, 29, and 59 kg P ha-1 while over-application of P at 117 kg ha-1 decreased SOC on low P soil. Out of six cropping sequences, soybean involving systems of continuous soybean, corn-soybean and soybean-cotton had higher C-footprint of 3.09, 3.09 and 2.48 kg CO2 eq. per kg yield, respectively. In conclusion, a corn involving crop sequence integrated with poultry litter as a winter bio-cover outperforms the other crop sequence and bio-cover systems in terms of serving as SOC and N sinks in microaggregates and enhancing soil C and N sequestration. The SOC and N stocks can be increased with appropriate P application on P deficient soils. Integration of continuous corn or cotton-corn with poultry litter reduces C-footprint but increase net C gain and sustainability index relative to the other cropping systems.


Chapter 2 of dissertation is accepted and ready for publishing in the Agronomy Journal.

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