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Site-Specific Analysis & Management

Hillslope Variability in Corn Response to Nitrogen Linked to In-Season Soil Moisture Redistribution

^a USDA-ARS, Bldg. 3702, Curtin Rd., University Park, PA 16802
^b Division of Plant Science, Univ. of Missouri, Columbia, MO 65211
^c Dep. of Crop and Soil Sciences, Pennsylvania State Univ., 116 ASI Bldg., University Park, PA 16802

^* Corresponding author (john.schmidt{at}ars.usda.gov)

Received for publication June 27, 2006. Spatial variability of corn (Zea mays L.) yield within a field is often identified as the primary criterion to justify site-specific nitrogen (N) management; yet, observed yield variability may be unrelated to N supply. The objective of this study was to characterize the spatial variability in economic optimum N rate (EONR) for corn. Ten plot locations were selected in 2005 along a 300-m toposequence of a field in central Pennsylvania. At each location, two replications of six N treatments (0, 56, 112, 168, 224, and 280 kg N ha^–1) were broadcast applied at planting as NH₄NO₃. Soil water content (0- to 90-cm depth) was recorded approximately weekly at each location between 5 June and 2 September. The quadratic-plateau response was selected as the most appropriate grain yield response function for 9 of 10 locations and for the field-mean response. The EONR ranged from 47 to 188 kg N ha^–1 among the nine locations, whereas EONR for the mean response was 137 kg N ha^–1. At four of nine locations, observed EONR deviated from field-mean EONR by 40 to 50 kg N ha^–1. The relationship between EONR and the change in soil profile water content (0–90 cm) between 30 June and 25 July (representing the driest and wettest soil conditions early in the growing season) was the defining relationship in this study (r² = 0.92; P > F < 0.0001). Successful site-specific N management depends on an evaluation of the spatial variability in EONR and the corresponding causal factors.

Abbreviations: EONR, economic optimum nitrogen rate

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