Estimated historical and current nitrogen balances for Illinois

Area of Science:

• Environmental Science
• Agricultural Science
• Ecology

Background:

• Midwestern rivers experience substantial nitrogen (N) exports, with Illinois and Iowa contributing the most per area.
• Human activities, particularly agriculture and drainage, significantly impact N cycles in Illinois.

Observation:

• Current annual N inputs in Illinois are approximately 800,000 Mg from fertilizer and 420,000 Mg from biological fixation (soybeans).
• These inputs exceed N exports in grain, creating a landscape N surplus.
• Rivers export about 50% of this surplus N, mainly as nitrate, with the rest denitrified or stored in soil organic matter.

Findings:

• Historical N losses from initial prairie cultivation (approx. 500,000 Mg N year(-1)) were comparable to contemporary levels.
• Riverine N flux was lowest around 1950 due to reduced N mineralization and fertilizer use.
• Current N export is linked to residual fertilizer N, biological N fixation, artificial drainage, and reduced crop diversity.

Implications:

• Understanding historical and current N dynamics is crucial for managing agricultural impacts on water quality.
• Agricultural practices significantly influence N cycling and export, necessitating sustainable management strategies.
• The study highlights the long-term consequences of agricultural intensification on nitrogen pollution.