Deep Soil Cores Reveal Large End‐of‐Season Residual Mineral Nitrogen Pool

• Published in: Agricultural & environmental letters Vol. 4; no. 1; pp. 1 - 4
• Main Authors: Hirsh, Sarah M., Weil, Ray R.
• Format: Journal Article
• Language: English
• Published: The American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc 2019; Wiley
• Subjects: cash crops; corn; groundwater; Mid-Atlantic region; nitrogen; risk; soil profiles; soybeans; summer; winter; Mid-Atlantic region
• ISSN: 2471-9625; 2471-9625
• DOI: 10.2134/ael2018.10.0055

Core Ideas Residual mineral N in 0‐ to 210‐cm‐deep soil following summer crops was evaluated. Soils contained a mean of 253 kg ha−1 mineral N, 115 kg ha−1 as NO3–N. 55% of mineral N was 90‐ to 210‐cm deep, where it is most at risk for leaching loss. More residual NO3–N remained after soybean than after corn. Awareness of residual deep N levels is essential to develop N conservation practices. The amount of mineral N remaining after cash crops informs agronomic and conservation practices. Few studies investigate mineral N below 30 cm, yet deeper N is more at risk for leaching to groundwater. We found, on average, 253 kg ha−1 of mineral N, 115 kg ha−1 in the NO3–N form, remaining after summer cash crop growth in the mid‐Atlantic region. Of this residual mineral N, 55% was 90 to 210 cm deep. More residual NO3–N remained after soybean than after corn. These substantial pools of mineral N remaining deep in the soil profile after productive cash crops, even unfertilized soybean, suggest that practices should be designed to scavenge residual N from deep soil layers in the fall, before it is lost over winter.