Date of Award

Fall 2024

Project Type

Thesis

Program or Major

Natural Resources and Environmental Studies

Degree Name

Master of Science

First Advisor

Stuart Grandy

Second Advisor

Serita Frey

Third Advisor

Richard Smith

Abstract

Nitrogen fertilizer is an essential aspect of modern agriculture; however, a substantial amount of applied nitrogen does not reach the crops it is intended for and leaches out of the soil. Soil organic matter and microbial activity are key regulators of the soil nitrogen cycle and the fate of nitrogen fertilizer. Understanding how fertilizer type impacts soil organic matter, nitrogen pools, and microbial activity will greatly improve our understanding regarding sustainable fertilizer application. To investigate this, I conducted an experiment using incubation with several fertilizer treatments and two soil types. I measured various soil nitrogen pools, soil respiration rates, and extracellular enzyme activity. The main findings of this study are that soil organic matter pools were not significantly affected by fertilizer nitrogen after 48 days of incubation, that the dissolved nitrogen pools were significantly affected by fertilizer application and incubation time and increased with increasing nitrogen additions, and that microbial activity was inconsistently affected by fertilizer additions. Dissolved inorganic nitrogen (DIN) ranged from 4.5-668 µg DIN g dry soil-1 in the New Hampshire soils and 4.5-556 µg DIN g dry soil-1 in the Nebraska soils Extracellular enzyme concentrations were significantly higher at 14 days after fertilizer application than 48 days and were not significantly affected by fertilizer type. The management implications of this study are that while fertilizer had minimal impacts on microbial processes, the rapid increase in bioavailable forms of N within 48 days of fertilizer application corresponding to fertilizer rate shows short-term boost in soil nutrient availability. This should improve plant uptake in the immediate period following fertilization, a critical time in crop growth.

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