Biologically based soil fertility in organic grain production systems

Ghimire, Binod

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https://hdl.handle.net/2142/125700 Copy

Description

Title

Biologically based soil fertility in organic grain production systems

Author(s)

Ghimire, Binod

Issue Date

2024-07-10

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

• Wander, Michelle M
• Ugarte, Carmen M

Doctoral Committee Chair(s)

Mulvaney, Richard L

Committee Member(s)

Margenot, Andrew J

Department of Study

Natural Res & Env Sci

Discipline

Natural Res & Env Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• SOM, soil organic matter
• POMC, particulate organic matter carbon
• POMN, particulate organic matter nitrogen
• PMN, potentially mineralizable nitrogen
• FDA, fluorescein diacetate hydrolysis
• POXC, permanganate oxidizable carbon
• RY, relative yield
• BG, β-D-glucosidase
• NAG, N-acetyl-β-glucosaminidase
• LAP: Leucine aminopeptidase
• RSA, root surface area
• RLD, root length density
• RD, root diameter
• SRL, specific root length

Abstract

This dissertation summarizes efforts undertaken to understand how measures of biological soil fertility can be used to optimize production and achieve environmental goals of diversified cropping systems that use a complex mixture of farming practices. One study investigated the labile carbon (C) and nitrogen (N) fractions in relation to management, site-specific factors, and corn (Zea mays L.) yield to determine whether these emerging biological indicators add value to routine soil testing regimes. In this study, soil samples (30 cm depth) were collected within two weeks of corn planting from forty-three organically managed corn fields located in the US Midwest. Records describing management practices applied during the 3- to 4-yr period prior to sampling were used to create typologies of organic N fertility, cropping intensity, and crop diversity. An N management category, which considered N added as animal, plant, or mix of animal and plant-based, was most strongly related to changes in labile C and N fractions. The concentrations of particulate organic matter C (POMC) and N (POMN) and potentially mineralizable N (PMN), as well soil inorganic N (p ≤ 0.10) were greater in fields managed with animal manure compared to green manure. Concentrations were intermediate in fields with mixed fertility sources. No significant relationships were found between cropping intensity and either emerging or routine soil fertility tests (p > 0.10). The crop diversity category was strongly related to POMC and potassium, where both were significantly greater under high than low crop diversity (p ≤ 0.10). In rotations that included perennials, crop diversity was also positively correlated with permanganate oxidizable C, fluorescein diacetate hydrolysis, and calcium (p ≤ 0.10). Site-specific soil and climatic factors exerted a stronger influence on both emerging and routine soil fertility tests than management categories. The POM fraction outperformed other indices in terms of its sensitivity to management and relationship to corn yield. A second study investigated if labile C and N fractions, fine root traits, and enzyme activities relevant to C and N cycling can be used to understand the interplay between different drivers of soil organic matter turnover, including organic N fertility inputs, corn genotypes, and weather in a crop-growing season. Measures were taken at pre-plant, V8, VT, and R2 growth stages. Notable weather variability experienced in the two years of this study (2019 and 2020) resulted in variable responses of the measured variables which provided an opportunity to explore differences in soil organic matter status and cycling driven by slow and fast processes altering organic inputs. Treatment effects were more prominent in 2019 than in 2020, when extreme weather events, including a hailstorm and derecho, caused foliar damage and reduced plant growth and biomass. Organic N additions increased some labile C and N fractions in a typical weather year. Genotypic effects were strongly expressed on fine root traits with root surface area (RSA) and root length density (RLD), being significantly greater in conventional than organically developed genotypes in both year (p < 0.05). A genotype by N interaction was apparent for fine root diameter (RD) and N-Acetyl- β-glucosaminidase (NAG) potential activity in the rhizosphere observed in 2019; when both metrices were greater in the genotype bred under organic conditions in the unamended N treatment (p < 0.05) than to cultivars bred conventionally. When corn transitioned from the V8 to VT stage, concentrations of POMC, POMN, and PMN declined, which were accompanied by increased inorganic N concentrations, RD, RSA, and RLD in both years. The potential activities of β-D-glucosidase, NAG, and leucine aminopeptidase were also higher in the rhizosphere than the bulk soil during this period in 2019. This temporal trend implies increased labile C and N turnover and elevated root exploration or foraging and root-soil interactions during the period of high plant N demand. Both studies suggest that POM may be used as an integrative soil measure that reveals SOM dynamics and N supply potential. Additional work should explore how to integrate POM to track responses of fine root traits and C and N cycle enzymes to improve genotype selection and nutrient management.

Graduation Semester

2024-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/125700

Copyright and License Information

Copyright 2024 Binod Ghimire

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