COMPARISON OF VADOSE ZONE NITRATE-N TO 50-YEAR RECORD OF NITROGEN FERTILIZER INPUTS ON NEBRASKA CROPLAND

Authors

• Kobi Benao, University of Nebraska-LincolnFollow

First Advisor

Daniel Snow

Second Advisor

Erin Haacker

Third Advisor

Arindam Malakar

Date of this Version

Fall 12-3-2021

Document Type

Article

Citation

Benao K. (2021). COMPARISON OF VADOSE ZONE NITRATE-N TO 50-YEAR RECORD OF NITROGEN FERTILIZER INPUTS ON NEBRASKA CROPLAND.

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In partial Fulfillment of Requirements For the degree of Master of Science, Major: Natural Resource Sciences, Under the supervision of Professor Daniel D. Snow. Lincoln, Nebraska: December 2021

Copyright © 2021 Kobi H. Benao

Abstract

Nitrogen (N) fertilizer has been applied in the United States (US) agricultural lands to boost crop production for decades. Excessive N fertilizer application and inefficient environmental management practices resulted in unintended consequences in the ecosystem and environment. Lack of spatially complete N fertilizer application time series data in the US makes N fertilizer quantification in the vadose zone challenging. In particular, the state of Nebraska needs spatial time series fertilizer maps to better address its N fertilizer input and potential nitrate-N (NO₃^--N) migration and storage in the vadose zone (VZ).

This study assesses 50 years of Nebraska N fertilizer application rate, cropping patterns, timings of application, land use, and soil type impact to NO₃^--N leaching then compared with estimated NO₃^--N mass stored in the BGMA in case study 1 and the Lower Platte South Natural Resources Districts (LPSNRD) case study 2 vadose zones.

A 50-year historical fertilizer application geospatial data analysis revealed that both study areas’ yearly N fertilizer consumption rates were different. In 1970, the BGMA and the LPSNRD total N consumption were about 30,000 tons. 50 years later the BGMA and the LPSNRD total N consumption increased to about 35, 000 tons. The BGMA N application rate for corn was 140 lbs-N/acre which then increased to 200 lbs-N/acre and 240 lbs-N/acre, respectively in 1970, 2010 and 2019. The LPSNRD N application rates for corn were about 80 lbs-N/acre, 160 lbs-N/acre, and 200 lbs-N/acre, respectively in 1970, 2010, and 2019 (Diagram 1). ANOVA analysis showed a statistically significant difference (p3^--N mass storage was found in both study area vadose zone which overlay with historically high N consumption rates. The BGMA D5-2014 and LPSNRD Waconda-1-2018 corn field total mass NO₃^--N stored in the vadose zone were compared. D5-2014 sandy soil has stored about 799 lbs-N/acre while Waconda-1-2018 silt clay loam stored about 2,600 lbs-N/acre.

50-year historical geospatial times series maps of N fertilizer application rates developed in this study could serve as an input guideline and management for communities to assess N fertilizer addition impacts to the vadose zone, thus impacting their groundwater and surface water.

Advisor: Daniel D. Snow