Long-term N fertilization imbalances potential N acquisition and transformations by soil microbes

Area of Science:

• Agricultural Science
• Soil Science
• Microbiology

Background:

• Nitrogen (N) fertilization is crucial for agriculture but has detrimental effects on soil ecosystem services, particularly microbial N transformation.
• Few studies comprehensively assess N-fertilization impacts across the entire N cycle within a single agricultural system.

Purpose of the Study:

• To investigate the long-term effects of increasing N fertilization rates on key microbial N cycle processes in continuous corn and corn-soybean rotations.
• To correlate changes in microbial N cycle gene abundances with soil property alterations.

Main Methods:

• Utilized real-time quantitative polymerase chain reaction (qPCR) to quantify microbial gene abundances.
• Targeted genes included nifH (N2 fixation), amoA (nitrification), nirK/nirS (denitrification), and nosZ (denitrification).
• Analyzed soil properties in conjunction with gene abundance data after 35 years of N fertilization.

Main Results:

• Long-term N fertilization increased fungal abundance, decreased soil pH, and altered nutrient availability.
• Significantly reduced nifH gene abundance, indicating impaired biological N2 fixation.
• Increased bacterial amoA gene abundance, suggesting accelerated nitrification, especially in continuous corn systems.
• No significant effect on the abundance of denitrifying microbial groups.

Conclusions:

• N fertilization in corn cropping systems diminishes microbial N2 acquisition and enhances nitrification.
• This creates a feedback loop, increasing agricultural system reliance on external nitrogen inputs.
• Highlights the need for sustainable N management strategies to mitigate negative ecosystem impacts.