Towards Rebalancing the Nitrogen Cycle: Development and Examination of Tools to Reduce Nitrogen Fertilizer Emissions from Crop Agriculture

Abstract

Nitrogen is a limiting nutrient in the growth of agricultural crops. To enhance yields and meet food demands, nitrogen fertilizers are added in excessive quantities during crop production. However, the use of these fertilizers is inefficient. An estimated 50% nitrogen fertilizer that is applied is not assimilated by crops and creates severe economic and environmental consequences. In order to develop effective interventions to this problem, the scientific community must first aim to quantify emissions with greater granularity and clarify the driving factors of inefficient nitrogen fertilizer use. Towards this aim, two separate modeling tools were developed to increase nitrogen emissions data availability and improve understanding of how practices and environmental conditions affect nitrogen use efficiency. In addition, a novel nitrogen fertilizer carrier was evaluated for its ability to aid in nitrogen emissions reduction in soil. First, to improve emissions data availability, a statistical model framework was developed to accurately predict daily nitrate loads (mean Kling-Gupta Efficiency of 0.74) in agricultural streams using streamflow and geographical data. Geographical variables related to nitrogen inputs (i.e., corn acreage density and livestock density) and water resources vulnerability (i.e., tile drainage density and water table depth) were highly correlated with nitrate loading concentrations. Next, a field-scale, process-based model was created to simulate nitrogen fertilizer dynamics during corn cultivation. Scenario modeling indicated that optimizing nitrogen application rates and delaying fertilizer application can reduce emissions to water and the atmosphere. Delayed application versus baseline aligns nitrogen availability in the root zone with peak crop demands, improving recovery rates. Based on these findings similar results in the literature, we hypothesized that nitrogen fertilizer inefficiency and emissions stem from rapid nitrogen transport and mismatched timing with crop needs. To avoid these dynamics, we explored using liposomes—micro-scale lipid carriers—to enhance nutrient retention and reduce transport in soil. Soil column experiments were conducted to analyze the fate and transport of these liposomes. Together, the research in this dissertation presents and evaluates new tools, both computational and technological, that fill research gaps and that could aid in the challenge of inefficient nitrogen fertilizer use