An evaluation of nitrogen indicators for soil health in long‐term agricultural experiments
Authors: Liptzin Daniel , Rieke Elizabeth L. , Cappellazzi Shannon B. , Bean G. Mac , Cope Michael , Greub Kelsey L. H. , Norris Charlotte E. , Tracy Paul W. , Aberle Ezra , Ashworth Amanda , Tavarez Oscar Bañuelos , Bary Andy I. , Baumhardt R. Louis , Gracia Alberto Borbón , Brainard Daniel C. , Brennan Jameson R. , Reyes Dolores Briones , Bruhjell Darren , Carlyle Cameron N. , Crawford James J. W. , Creech Cody F. , Culman Steve W. , Deen Bill , Dell Curtis J. , Derner Justin D. , Ducey Thomas F. , Duiker Sjoerd W. , Dungan Robert S. , Dyck Miles F. , Ellert Benjamin H. , Entz Martin H. , Solorio Avelino Espinosa , Fonte Steven J. , Fonteyne Simon , Fortuna Ann‐Marie , Foster Jamie L. , Fultz Lisa M. , Gamble Audrey V. , Geddes Charles M. , Griffin‐LaHue Deirdre , Grove John H. , Hamilton Stephen K. , Hao Xiying , Hayden Zachary D. , Honsdorf Nora , Howe Julie A. , Ippolito James A. , Johnson Gregg A. , Kautz Mark A. , Kitchen Newell R. , Kumar Sandeep , Kurtz Kirsten S. M. , Larney Francis J. , Lewis Katie L. , Liebman Matt , Ramirez Antonio Lopez , Machado Stephen , Maharjan Bijesh , Gamiño Miguel Angel Martinez , May William E. , McClaran Mitchel P. , McDaniel Marshall D. , Millar Neville , Mitchell Jeffrey P. , Moore Amber D. , Moore Philip A. , Gutiérrez Manuel Mora , Nelson Kelly A. , Omondi Emmanuel C. , Osborne Shannon L. , Alcalá Leodegario Osorio , Owens Phillip , Pena‐Yewtukhiw Eugenia M. , Poffenbarger Hanna J. , Lira Brenda Ponce , Reeve Jennifer R. , Reinbott Timothy M. , Reiter Mark S. , Ritchey Edwin L. , Roozeboom Kraig L. , Rui Yichao , Sadeghpour Amir , Sainju Upendra M. , Sanford Gregg R. , Schillinger William F. , Schindelbeck Robert R. , Schipanski Meagan E. , Schlegel Alan J. , Scow Kate M. , Sherrod Lucretia A. , Shober Amy L , Sidhu Sudeep S. , Moya Ernesto Solís , Luce Mervin St. , Strock Jeffrey S. , Suyker Andrew E. , Sykes Virginia R. , Tao Haiying , Campos Alberto Trujillo , Van Eerd Laura L. , van Es Harold M. , Verhulst Nele , Vyn Tony J. , Wang Yutao , Watts Dexter B. , Wright David L. , Zhang Tiequan , Morgan Cristine L. S. , Honeycutt C. Wayne 
Published: May 2023

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.