An evaluation of nitrogen indicators for soil health in long‐term agricultural experiments
Daniel Liptzin, Elizabeth L. Rieke, Shannon B. Cappellazzi, G. Mac Bean, Michael Cope, Kelsey L.H. Greub, Charlotte E. Norris, P. W. Tracy, Ezra Aberle, Amanda J. Ashworth, Oscar Bañuelos Tavarez, Andy I. Bary, R. Louis Baumhardt, Alberto Borbón Gracia, Daniel C. Brainard, Jameson R Brennan, Dolores Briones Reyes, Darren Bruhjell, Cameron N. Carlyle, James J.W. Crawford, Cody F. Creech, Steve W. Culman, Bill Deen, Curtis J. Dell, Justin Derner, Thomas F. Ducey, Sjoerd W. Duiker, Robert S. Dungan, Miles Dyck, Benjamin H. Ellert, Martin H. Entz, Avelino Espinosa Solorio, Steven J. Fonte, Simon Fonteyne, Ann‐Marie Fortuna, Jamie L. Foster, Lisa M. Fultz, Audrey V. Gamble, Charles M. Geddes, Deirdre Griffin‐LaHue, John H. Grove, Stephen K. Hamilton, Xiying Hao, Zachary D. Hayden, Nora Honsdorf, Julie A. Howe, James A. Ippolito, Gregg A. Johnson, Mark A. Kautz, Newell R. Kitchen, Sandeep Kumar, Kirsten S.M. Kurtz, Francis J. Larney, Katie L. Lewis, Matt Liebman, Antonio López Ramírez, Stephen Machado, Bijesh Maharjan, Miguel Ángel Martínez Gamiño, William E. May, Mitchel P. McClaran, Marshall D. McDaniel, N. Millar, Jeffrey P. Mitchell, Amber Moore, P. Moore, Manuel Mora Gutiérrez, Kelly A. Nelson, Emmanuel C. Omondi, Shannon L. Osborne, Leodegario Osorio Alcalá, Phillip Owens, E. M. Pena‐Yewtukhiw, Hanna Poffenbarger, Brenda Ponce Lira, Jennifer R. Reeve, Timothy M. Reinbott, Mark S. Reiter, Edwin L. Ritchey, Kraig L. Roozeboom, Yichao Rui, Amir Sadeghpour, Upendra M. Sainju, Gregg R. Sanford, William F. Schillinger, Robert R. Schindelbeck, Meagan E. Schipanski, Alan J. Schlegel, Kate M. Scow, Lucretia A. Sherrod, Amy L. Shober, Sudeep S. Sidhu, Ernesto Solís Moya, Mervin St. Luce, Jeffrey S. Strock, Andrew E. Suyker, Virginia R. Sykes, Haiying Tao, Alberto Trujillo Campos, Laura L. Van Eerd
Abstract
Abstract Various soil health indicators that measure a chemically defined fraction of nitrogen (N) or a process related to N cycling have been proposed to quantify the potential to supply N to crops, a key soil function. We evaluated five N indicators (total soil N, autoclavable citrate extractable N, water‐extractable organic N, potentially mineralizable N, and N ‐acetyl‐β‐ D ‐glucosaminidase activity) at 124 sites with long‐term experiments across North America evaluating a variety of managements. We found that 59%–81% of the variation in N indicators was among sites, with indicator values decreasing with temperature and increasing with precipitation and clay content. The N indicators increased from 6%–39% in response to decreasing tillage, cover cropping, retaining residue, and applying organic sources of nutrients. Overall, increasing the quantity of organic inputs, whether from increased residue retention, cover cropping, or rotations with higher biomass, resulted in higher values of the N indicators. Although N indicators responded to management in similar ways, the analysis cost and availability of testing laboratories is highly variable. Further, given the strong relationships of the N indicators with carbon (C) indicators, measuring soil organic C along with 24‐h potential C mineralization could be used as a proxy for N supply instead of measuring potentially mineralizable N or any other N indicator directly.