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SPATIAL VARIABILITY

Appropriateness of Management Zones for Characterizing Spatial Variability of Soil Properties and Irrigated Corn Yields across Years

^a USDA-ARS, and Dep. of Agron. and Hortic., Univ. of Nebraska, Lincoln, NE 68583
^b USDA-ARS, Northern Great Plains Res. Lab., Mandan, ND 58554
^c Embrapa Meio Ambiente, Jaguariuna, SP, Brazil

^* Corresponding author (jshanahan1{at}unl.edu).

Received for publication August 18, 2003. Recent precision-agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZ that characterize spatial variation in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field. A georeferenced soil-sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997–2001) seasons. The five landscape attributes were aggregated into four MZ using principal-component analysis of landscape attributes and unsupervised classification of principal-component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest- and lowest-yielding MZ in three of five seasons, receiving average precipitation, less-pronounced (5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions.

Abbreviations: CV, coefficient of variation • DGPS, differential global positioning system • DN, digital number • EC, electrical conductivity • EC_a, apparent electrical conductivity • GIS, geographical information systems • MZ, management zones • OM, organic matter • PC, principal component • PCA, principal-component analysis

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