An Examination Of Various Segments Of The Nitrogen Cycle In Diverse Agro-Ecosystems

Nitrogen is essential to plant growth and biomass production. Thus, it is often the primary focus in agricultural literature. The nitrogen cycle is complex in terrestrial systems mainly because it takes various forms - occurring in all chemical phases and mediated by both biotic and abiotic processes. The first chapter of this study examined the nitrogen cycle in its entirety as it relates to corn production in Iowa. Ultimately, this study was a proof-of-concept illustrating the possibility of adaptive nitrogen fertilization through the use of model simulation and improved VNIR and GIS technologies. The next two chapters focused more specifically on gaseous nitrous oxide production in traditionally manured agroecosystems and potential interactions with carbon quality and quantity through the use of cover crops. Significant differences were found in the N2O emissions profiles between manured (M) and unmanured (NM) soils with a simultaneous increasing trend in emissions with increasing fertilizer applications. M soils produced 53-, 15.5- and 8.6-fold increases in N2O emissions over NM soils. Furthermore, on manured soils this study found that nitrous oxide emissions in cover crop treatments (winter rye and oats) showed no significant difference over a control plot during the early spring season. However, as ambient temperatures warmed, winter rye was found to decrease average N2O emissions by approximately 70% when compared to either the oat or fallow treatment. Additionally, nitrate concentrations found in leachate at 55 cm were dramatically lower in rye plots, while the winter-killed oat showed no decrease in nitrate concentrations when compared to a control. The final chapter concludes with a study on nitrogen mineralization in a Kenyan chronosequence amended with organic materials (Maize (MA) and Faidherbia albida (FA)). Mineralization patterns followed a similar trend in soils from a recent (New) and much older conversion (Old) to agriculture. Average mineralization in FA amended soils was 4.31% greater than the Control in the New soil and 0.75% in the Old soil during mineralization phases. In contrast, the MA treatment immobilized nitrogen for the majority of the study in both soils and to a greater extent in the more fertile New soil