Variability in soil properties across agricultural landscapes in interaction with annual climatic variations affects crop response to N fertilizer applications and is a major challenge for development of effective N fertilizer practices that increase crop yield and reduce environmental N losses. The objectives of this research were to assess spatial differences in soil N availability in fields with poorly drained claypan soils containing low-lying or depressional areas and to determine the spatial variability in relative crop response and economic returns with application of enhanced-efficiency N fertilizers (EEF) compared with those of urea. A field trial (planted with corn (Zea mays L.)) was conducted in 2007 and 2008 in a claypan soil in northeastern Missouri that contained both side slope and low-lying landscape positions. Preplant N fertilizer treatments consisted of a nontreated control and 168 kg N ha−1 of urea, polymer-coated urea (PCU), urea + urease inhibitor (UI), and urea + nitrification inhibitor (NI). Grain yield response across landscape positions was ranked PCU > NI ≥ UI ≥ urea for 2007 and PCU > UI ≥ NI ≥ urea in 2008. Further mapping of yield differences from EEF compared with those of urea indicated areas of the field with yield benefits of up to approximately 5,100 kg ha−1 in 2007 and 7,100 kg ha−1 in 2008 with application of PCU, but some areas of negative yield differences were also observed. A variable-source N fertilizer strategy with use of EEF targeted to specific landscape positions and conventional N fertilizers used in the other parts of the field may be a possible management option in claypan soils or other poorly drained soils that include depressional or low-lying areas.
1Department of Soil, Environmental and Atmospheric Sciences, University of Missouri, Columbia, Missouri, USA.
2Division of Plant Sciences, University of Missouri, Novelty, Missouri, USA.
3Department of Forestry, University of Missouri, Columbia, Missouri, USA.
Address for correspondence: Dr. Peter P. Motavalli, Department of Soil, Environmental and Atmospheric Sciences, University of Missouri, 302 ABNR Bldg, Columbia, MO 65211, USA. E-mail: firstname.lastname@example.org
Financial Disclosures/Conflicts of Interest: This study was supported by a grant from the Missouri Fertilizer and Aglime Board. The authors have no conflicts of interest to report.
Received August 10, 2012.
Accepted for publication November 13, 2012.