Economically optimal nitrogen rate reduces soil residual nitrate

Area of Science:

• Agronomy
• Soil Science
• Environmental Science

Background:

• Post-harvest residual soil nitrate-nitrogen (RSN) can leach into water resources.
• Minimizing RSN is crucial for reducing nitrogen loss to the environment.

Purpose of the Study:

• To evaluate if applying nitrogen (N) fertilizer at the economically optimal N rate (EONR) reduces RSN after corn harvest compared to current producer practices.
• To compare RSN levels across N fertilizer rates below, at, and above the EONR.

Main Methods:

• Six field experiments were conducted in Missouri over two years across three major soil areas.
• N fertilizer rates from 0 to 280 kg N ha⁻¹ were applied, EONR determined, and RSN measured to a 0.9-m depth.

Main Results:

• Average RSN at the EONR was 33 kg N ha⁻¹, at least 12 kg N ha⁻¹ lower than at producers' N rates.
• RSN increased with applied N above the EONR, and a plateau-linear model described the relationship.
• Excessive N application above EONR consistently elevated RSN levels.

Conclusions:

• Applying N fertilizer at the EONR offers environmental benefits while remaining economically viable.
• Accurate prediction of EONR is essential for sustainable nitrogen management in agriculture.