Does inorganic nitrogen fertilization improve soil aggregation? Insights from two long-term tillage experiments

Area of Science:

• Agricultural Science
• Soil Science
• Agronomy

Background:

• Understanding the effects of inorganic fertilization on soil aggregation is crucial for sustainable agriculture.
• Long-term studies are needed to elucidate the complex interactions between nitrogen (N) fertilization, tillage, and soil structure.

Purpose of the Study:

• To investigate the cumulative impacts of nitrogen fertilization on soil aggregation, soil organic carbon (SOC), and pH.
• To examine these effects across different tillage systems (chisel plow, ridge till, moldboard plow, reduced till, no-till) and cropping systems (continuous corn, corn-soybean) under irrigated and rainfed conditions.

Main Methods:

• Field experiments were conducted over 27-28 years in Nebraska, applying various rates of N fertilizer (0-300 kg N/ha) to continuous corn and corn-soybean rotations.
• Soil samples were analyzed for mean weight diameter of water-stable aggregates (MWDA), SOC, and pH at different depths.

Main Results:

• Nitrogen fertilization altered soil aggregation in continuous corn across tillage systems.
• MWDA increased in the near-surface (0-7.5 cm) in no-till but decreased significantly in deeper layers (7.5-60 cm) with N application.
• Soil pH decreased with N fertilization, while SOC showed little change. No-till and reduced till systems exhibited superior near-surface aggregation compared to moldboard plow.

Conclusions:

• Long-term nitrogen fertilization can enhance near-surface soil aggregation in no-till continuous corn systems but may negatively impact subsoil aggregation.
• Applying N fertilizer at rates around 80 kg N/ha appears to minimize soil aggregation deterioration.
• Tillage practices significantly influence the response of soil aggregation to N fertilization.