Tillage and Fertilizer Management Effects on Phosphorus Runoff from Minimal Slope Fields

Area of Science:

• Agronomy and Soil Science
• Environmental Science
• Agricultural Engineering

Background:

• Phosphorus (P) fertilization is crucial for crop production but can lead to increased P losses in surface runoff.
• Limited data exists on P runoff losses from low-slope (<2%) fields common in the US Midwest.
• Tillage and fertilizer placement methods are key factors influencing nutrient loss.

Purpose of the Study:

• To evaluate the impact of tillage-fertilizer placement methods on phosphorus (P) runoff.
• To assess the effect of fall P fertilization rates on P concentrations and loads in runoff.
• To determine the influence of these practices on corn and soybean grain yields.

Main Methods:

• Simulated fall and spring runoff events were used to measure P concentrations and loads.
• Tillage-fertilizer placements included no-till broadcast, strip-till broadcast, and strip-till deep placement (-15 cm subsurface band).
• Fall P fertilizer rates of 0, 52, and 90 kg P₂O₅ ha⁻¹ were applied.

Main Results:

• Deep placement significantly reduced dissolved reactive P (DRP) loads by 69-72% compared to broadcast methods.
• DRP and total P (TP) concentrations increased with higher P rates for broadcast applications but remained low with deep placement.
• Deep banding P did not reduce crop yields but effectively minimized P runoff losses, especially at high application rates.

Conclusions:

• Subsurface deep banding of phosphorus is a highly effective strategy for reducing P losses in surface runoff from low-slope agricultural fields.
• This placement method mitigates the risk of increased P runoff associated with higher fertilization rates.
• Deep placement offers a viable solution for sustainable P management in vulnerable agricultural landscapes.