Nitrate and phosphorus leaching, surface soil nitrate concentrations, and nutrient balances under conservation tillage and cover crops in central Illinois

Taracena Aldana, Javier Enrique

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https://hdl.handle.net/2142/130064 Copy

Description

Title

Nitrate and phosphorus leaching, surface soil nitrate concentrations, and nutrient balances under conservation tillage and cover crops in central Illinois

Author(s)

Taracena Aldana, Javier Enrique

Issue Date

2025-07-24

Director of Research (if dissertation) or Advisor (if thesis)

Margenot, Andrew J

Committee Member(s)

• Yu, Zhongjie
• Preza, Giovani

Department of Study

Crop Sciences

Discipline

Crop Sciences

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Tile drainage
• Nutrient leaching
• Maize–soybean rotation
• Cover cropping
• Ion-exchange resin lysimeters
• Nutrient balances

Abstract

Tile drainage systems in the U.S. Midwest support high-yield maize–soybean production but also promote nitrogen (N) and phosphorus (P) losses to surface waters, contributing to downstream eutrophication and hypoxia. Conservation practices such as reduced tillage and cover cropping have been proposed to mitigate nutrient leaching, yet their effectiveness in tile-drained systems and their alignment with agronomic nutrient balances remain poorly understood. This thesis investigates how tillage and cover cropping influence nitrate-N and phosphate-P losses, surface soil nitrate-N concentrations, and N and P balances in a tile-drained maize–soybean rotation in central Illinois. Field experiments were conducted from 2021 to 2024 under four management practices: chisel tillage (CT), no tillage (NT), strip tillage (ST), and strip tillage with cover crops (STCC). Nitrate-N and phosphate-P losses were quantified through continuous monitoring of subsurface tile drains. Ion-exchange resin (IER) lysimeters installed at 40 cm depth were evaluated as a potential alternative to tile drains for estimating nutrient loads. Biweekly surface soil samples (0–15 cm) were collected to assess nitrate-N concentrations and their potential as indicators of leaching losses and evaluate seasonal trends. In the 2023–2024 seasons, nutrient balances were calculated using inputs from fertilizer and biological N fixation and outputs from grain removal, measured leaching losses and gaseous emissions. Cumulative four-year nitrate-N loads in tile drainage were highest under CT (116.2 kg N ha⁻¹) and NT (110.4 kg N ha⁻¹), and significantly lower under ST (90.9 kg N ha⁻¹) and STCC (90.6 kg N ha⁻¹), representing a 22–25% reduction in nitrate-N export with strip tillage practices (p < 0.001). Phosphate-P loads remained low across treatments (≤0.74 kg P ha⁻¹), with ST and STCC reducing losses significantly compared to NT (p < 0.001). Surface soil nitrate-N concentrations increased following side-dress N fertilization in maize and varied by year, crop phase, and treatment. However, correlations between surface concentrations and tile nitrate-N loads were generally weak (overall R² = 0.23, p < 0.001), though higher in isolated cases such as NT during maize (R² = 0.91, p = 0.1), indicating limited predictive power. IER lysimeters consistently overestimated nutrient losses compared to tile measurements—by factors of 9–12 for nitrate-N and 140–280 for phosphate-P. Despite this overestimation, lysimeters captured consistent treatment-level patterns and seasonal trends (nitrate-N: F = 1.67; phosphate-P: F = 0.53). However, IER lysimeters reflect nutrient movement only at 40 cm depth, whereas subsurface tile drainage loads integrate losses from deeper soil layers where additional processes such as denitrification and P sorption can occur. Their strong sensitivity to management effects and practicality for shallow monitoring support their continued development for field-scale nutrient assessment. Nitrogen balances exhibited surpluses during maize phases due to high fertilizer inputs and deficits during soybean phases, where biological N fixation did not fully compensate for grain N removal. Across the two-year period, all treatments resulted in cumulative N and P deficits, with STCC showing the largest N deficit (–72.1 kg N ha⁻¹) due to higher grain removal, and NT the largest P deficit (–25.97 kg P ha⁻¹) resulting from relatively high grain P removal combined with limited replenishment through fertilization. Grain harvest was the dominant driver of nutrient export across treatments. Agronomic N balances were not predictive of tile nitrate-N losses (R² = 0.000, p = 0.991), while P balances showed a moderate correlation with tile phosphate-P losses (R² = 0.29, p = 0.002). The lack of correspondence between N balances and leaching may reflect additional N sources, such as soybean residue mineralization, that are not accounted for a simple input-output budgets, highlighting that nutrient balances alone do not adequately capture environmental loss potential, particularly for N. Together, these findings demonstrate that strip tillage and cover cropping can reduce nutrient leaching while supporting high crop productivity, though they may intensify nutrient depletion by immobilizing or removing nutrients taken up during cover crop growth, particularly with early or delayed termination that limits nutrient release prior crop uptake. None of the management systems met the 45% nitrate-N and total P reduction goals outlined in Illinois’ Nutrient Loss Reduction Strategy, emphasizing the need for integrative nutrient and water management approaches. Reliance on surface soil nitrate concentrations or lysimeter estimates without calibration may lead to misinterpretation of loss risk. Instead, combined monitoring of subsurface drainage, surface soils, lysimeter data, and nutrient budgets offers a more complete understanding of nutrient fate under conservation practices in tile-drained systems. This research highlights the complexity of nutrient management in intensively farmed, tile-drained landscapes and supports the need for site-specific strategies that simultaneously address agronomic and environmental objectives in central Illinois and the broader Upper Midwest.

Graduation Semester

2025-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/130064

Copyright and License Information

Copyright 2025 Javier Taracena Aldana

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