About Us | Help Videos | Contact Us | Subscriptions
 

Members of ASA, CSSA, and SSSA: Due to system upgrades, your subscriptions in the digital library will be unavailable from May 15th to May 22nd. We apologize for any inconvenience this may cause, and thank you for your patience. If you have any questions, please call our membership department at 608-273-8080.

 

Institutional Subscribers: Institutional subscription access will not be interrupted for existing subscribers who have access via IP authentication, though new subscriptions or changes will not be available during the upgrade period. For questions, please email us at: queries@dl.sciencesocieties.org or call Danielle Lynch: 608-268-4976.

Abstract

 

This article in JEQ

  1. Vol. 37 No. 3, p. 1073-1085
     
    Received: Jan 5, 2007


    * Corresponding author(s): ctgreen@usgs.gov
 View
 Download
 Alerts
 Permissions
Request Permissions
 Share

doi:10.2134/jeq2007.0010

Nitrogen Fluxes through Unsaturated Zones in Five Agricultural Settings across the United States

  1. Christopher T. Green *a,
  2. Lawrence H. Fisherb and
  3. Barbara A. Bekinsa
  1. a US Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025
    b US Geological Survey, 160 N Stephanie St., Henderson, NV 89074

Abstract

The main physical and chemical controls on nitrogen (N) fluxes between the root zone and the water table were determined for agricultural sites in California, Indiana, Maryland, Nebraska, and Washington from 2004 to 2005. Sites included irrigated and nonirrigated fields; soil textures ranging from clay to sand; crops including corn, soybeans, almonds, and pasture; and unsaturated zone thicknesses ranging from 1 to 22 m. Chemical analyses of water from lysimeters and shallow wells indicate that advective transport of nitrate is the dominant process affecting the flux of N below the root zone. Vertical profiles of (i) nitrogen species, (ii) stable isotopes of nitrogen and oxygen, and (iii) oxygen, N, and argon in unsaturated zone air and correlations between N and other agricultural chemicals indicate that reactions do not greatly affect N concentrations between the root zone and the capillary fringe. As a result, physical factors, such as N application rate, water inputs, and evapotranspiration, control the differences in concentrations among the sites. Concentrations of N in shallow lysimeters exhibit seasonal variation, whereas concentrations in lysimeters deeper than a few meters are relatively stable. Based on concentration and recharge estimates, fluxes of N through the deep unsaturated zone range from 7 to 99 kg ha−1 yr−1 Vertical fluxes of N in ground water are lower due to spatial and historical changes in N inputs. High N fluxes are associated with coarse sediments and high N application rates.

  Please view the pdf by using the Full Text (PDF) link under 'View' to the left.

Copyright © 2008. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyAmerican Society of Agronomy, Crop Science Society of America, and Soil Science Society of America