Beyond corn as king: Addressing water quality and soil organic carbon decline in maize-based agroecosystems

Nakayama, Yuhei

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https://hdl.handle.net/2142/127351 Copy

Description

Title

Beyond corn as king: Addressing water quality and soil organic carbon decline in maize-based agroecosystems

Author(s)

Nakayama, Yuhei

Issue Date

2024-11-20

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

Margenot, Andrew J

Doctoral Committee Chair(s)

Margenot, Andrew J

Committee Member(s)

• Lee, DoKyoung
• McSweeney, Kevin
• Wagai, Rota

Department of Study

Crop Sciences

Discipline

Crop Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• nitrate leaching
• soybean
• soil organic carbon stock
• mollisols
• crop rotation
• soil fertility management

Abstract

The maize-dominated cropping systems in central North America are one of the most productive agroecosystems globally with relatively high nutrient demands. Crop production relies on high fertilizer input, in addition to the inherently high fertility of soils in this region. The increasing size of hypoxic zone in the Gulf of Mexico and decreasing soil organic matter across croplands have raised concerns for the sustainability of the crop production in the region. Management practices that mitigate off-field nutrient losses and soil organic carbon (SOC) depletion are key for sustaining productive cropping systems. Though the management of maize has been the focus of mitigation practices in the region, in particular for nutrient loss, this dissertation evaluates components beyond the maize phase. Specifically, the soybean phase of widely practiced corn-soybean rotation and extended maize-based rotations were evaluated to respectively address the concerns for the declining water quality and soil organic matter. The specific objectives of this dissertation were to 1) evaluate optimum phosphorus management of soybean to mitigate nitrogen (N) losses while maintaining productivity, 2) mitigate inorganic N leaching loss from Illinois soybean production by substituting ammonium phosphate fertilizers with N-free triple superphosphate fertilizers, and 3) assess centennial-scale effect of diversified crop rotation and fertilization on SOC stocks as well as 4) particulate and mineral-associated organic carbon under maize-based annual cropping system converted from SOC-rich tallgrass prairie in central North America. To address the first two objectives, soybean productivity and inorganic N leaching losses were evaluated in field experiments over four site-years testing phosphorus fertilizer sources (monoammonium phosphate, diammonium phosphate, triple superphosphate), rates (full and partial maintenance rate), and timing-placement (fall broadcasting, spring broadcasting, spring banding) on the two dominant soil types (Mollisols and Alfisols) of maize-based cropping systems in Illinois and greater central North America. As hypothesized, substitution of the commonly applied ammonium phosphates with N-free triple superphosphates supported comparable grain yield and phosphorus removal, which were unresponsive to rate and timing-placement. Though 30.0–49.9 NO3-N ha-1 lower off-season nitrate loads following fall application of triple superphosphate relative to ammonium phosphates on Mollisols in the first year support the hypothesized water quality benefit of triple superphosphate over ammonium phosphates, high non-fertilizer nitrate leaching generally outstripped the variation in N co-applied across fertilizer sources and rates. Reduction in nitrate loads unexpectedly exceeded the amount of N co-applied as ammonium phosphates (13.6–23.0 kg N ha-1), suggesting phosphorus fertilizer source influenced non-fertilizer nitrate leaching and all of N from ammonium phosphates was lost. Even though the N loss mitigation efforts in the Corn Belt of central North America generally focused on N fertilizer input to maize, the high non-fertilizer nitrate leaching loads regardless of fertilization under soybean suggest mitigating N loss from soybean via cover cropping can be comparably significant. To address the third and fourth objectives, soils were sampled in year 145 of the Morrow Plots, the second oldest continuous agricultural experiment in the world located at University of Illinois Urbana-Champaign, to evaluate organic carbon stocks of bulk soils (0–90 cm) and density fractions (0–45 cm) across long-term crop rotation and fertility management treatments. In addition, contributions of maize- versus prairie-derived SOC (0–45 cm) were estimated by δ13C analysis. Higher bulk SOC stocks on equivalent soil mass-basis (+30.7 Mg C ha-1 or +31.7%) under maize-oat-alfalfa relative to continuous maize supported the hypothesized advantages of diversified rotation in mitigating SOC losses. Though SOC stocks by equivalent soil mass were similar across fertility management, surface and subsurface SOC stocks differentially responded to NPK fertilization under continuous maize and maize-soybean, demonstrating the importance of including subsoil for SOC stock evaluation. Particulate and mineral-associated organic carbon stocks were similarly higher, with comparable proportional increases, under maize-oat-alfalfa than continuous maize as expected. In contrast to our hypothesis, the majority of SOC in 0–45 cm was still derived from former tallgrass prairie, despite 145 years of continuous maize cropping. Limited offset of prairie SOC loss by maize SOC suggests the importance of understanding the role of relic prairie soil organic matter in supporting future crop production in central North America. This dissertation illustrates the importance of evaluation beyond maize phase of maize-dominated agroecosystems to mitigate water quality and soil organic matter decline in central North America. Specifically, the studies demonstrate the high contribution of soybean cropping to off-field nitrate loads despite not receiving N fertilization and limited capacity of maize-derived SOC to offset losses of prairie-derived SOC. The findings from the two field experiments suggest the potential of temporal crop diversification via cover cropping and crop rotation to mitigate off-field nutrient loss and SOC decline, though the outcomes of implementing temporal crop diversification likely vary by agroecosystem context. Comprehensive evaluation of cropping system, rather than focusing on the dominant player (e.g., maize phase), is important for understanding biogeochemical cycling of agroecosystems and identify management practices to mitigate environmental impact of crop production. Given the uncertainties from ongoing global climate change, providing farmers with diverse options, carefully assessed with research experiments, to mitigate water quality and soil organic matter decline, is critical for sustainable crop production in central North America.

Graduation Semester

2024-12

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/127351

Copyright and License Information

Copyright 2024 Yuhei Nakayama

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