On-farm evaluation of nitrogen use efficiency and nutrient balances at the intra-field scale in north-central Illinois

Farmers in the Midwestern USA are among the most highly productive and efficient producers of corn (Zea may L.) and soybeans (Glycine max) grain in the world. Despite this, the region’s Mississippi River Basin faces water quality challenges from losses of nitrate-nitrogen (N) and phosphorus (P) to the Gulf of Mexico, making improved nutrient management in the region a priority. In Illinois, the statewide strategy to reduce nutrient losses from agriculture highlights a set of so-called best management practices (BMPs) with potential to decrease in-infield nutrient loss risk based on research results from the plot scale. However, few studies have evaluated the range of potential outcomes from BMPs at the field-scale on commercial grain production farms in Illinois. Our primary objective of this thesis was to contextualize agronomic outcomes at the intra-field and field scale to understand the complexity of on-farm nutrient management in fields currently operating under BMPs in Illinois. To support this objective, we measured N use efficiency (NUE), agronomic nutrient balances (ANB), soil nutrient stocks and nutrient leaching losses across twelve fields for two years in Bureau County, Illinois, with a total of 98 intra-field sampling zones (n = 80 in 2022, n = 98 in 2023). The first chapter of this thesis focuses on testing hypotheses related to variability within and discrepancies between NUE terms at the intra and inter-field scales for corn and relationships of NUE terms to one another, yield, N application rate, and soil physiochemical properties related to N. We found greater intra than inter-field variability for all terms across both years, a significant difference between terms was also present between 2022 and 2023. Terms with similar calculation methods, partial factor productivity (PFP) and partial nutrient balances (PNB), showed strong relationships to each other, yield, and N rate while direct measurement of N derived from fertilizer (Ndff) using 15N isotopes and by difference method by agronomic efficiency (AE) were unrelated to other terms and only Ndff and yield were correlated. Inconsistent relationships between terms, soil nutrient stocks, and particle size factors from surface (0-15 cm) to subsurface (45-60 cm) depths indicated a lack of direct relationship between soil N stocks and NUE. Additionally, NUE terms were not related to end of growing season inorganic nitrate concentrations nor in-season nutrient losses, highlighting the complexity of nutrient fates on-farm even under relatively high NUE. In the second chapter we constructed two-year ANBs of N,P, and K across 9 fields in a corn-soybean rotation and 3 fields in a corn-corn rotation to evaluate the intra-field variability of ANBs on-farm, measured the impact of assumed vs measured grain nutrient concentrations on the accuracy of ANB values, evaluated a normalized ANB metric to contextualize further balances, and quantified relationships between ANBs, soil nutrient stocks, and soil nutrient losses. Net differences in ANBN values were significant for corn but not for soybeans, with a two-year net difference approximately equivalent to ~20-50% of N application rates in the corn phase. If combined with document variability in soybean biological nitrogen fixation (BNF), this uncertainty in NANB values could exceed N inputs in the corn rotation phase, with N input from soybean BNF alone equivalent to 50-100% of corn N rate in some cases. While most observations for P indicated overestimation of nutrient removal with assumed nutrient concentrations, results were not significantly different. Despite this, net two-year differences between ANBs with differing nutrient concentrations were 30-50% of annual P removal by corn or soybean crop, while differences in removal estimates for K were circumneutral. Constructed ANBs showed greater variability at the intra-field versus inter-field scale, however the range in variability was significantly greater for N, followed by K and P. Soil particle size was correlated to intra-field ANB values of N and P, while differing trends were observed between total P and Mehlich-3 P stocks with PANB depending on depth. In addition, ANBs of N and P were also correlated to recovered nutrient leaching losses of nitrate-N and dissolved P, and particle size relationships emerged with nitrate-N losses but only at pedon depths. This study highlights multiple avenues of certainty in ANBs, especially for N, that are critical to consider and further evaluate to improve usage of N balances. We also identified relationships between ANB, soil nutrient stocks, particle size properties, and nutrient losses from multiple depths on-farm, that while variable, can help to further contextualize agronomic and environmental outcomes on farm.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Bergschneider, Luke Joseph

Contributors dc:contributor

• Margenot, Andrew
• Mulvaney, Richard
• Preza Fontes, Giovani
• Jones, John

• Nitrogen Use Efficiency
• Nutrient Balances
• On-farm
• Nue

Statement dc:rights

• Copyright 2024 Luke Bergschneider

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/125738

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F125738