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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

View larger version (217K): [in a new window]   Fig. 1. Bare soil aerial image of Gibbon, NE, corn study site acquired in spring of 1999. Map symbols and boundaries are depicted for the Hobbs (2Hb) and Uly (HbA and UHC2) soil series, which are present in this field (USDA Soil Conserv. Serv., 1974). The Hobbs series consists of deep, medium-textured, well-drained, nearly level to gently sloping soils formed in water-deposited silts while the Uly series consists of deep, well-drained, medium-textured, moderately to strongly sloping soils formed in calcareous loess.

View larger version (65K): [in a new window]   Fig. 2. (Top) Gray-scale maps of five landscape attributes acquired at the Gibbon, NE, corn study site consisting of red, green, and blue bands (shown in one map) of soil brightness image, elevation, and apparent electrical conductivity (ECa), with variations in color, from dark to light, corresponding to increasing values for all landscape attributes. (Middle) Gray-scale maps of principal-component (PC) scores for PCs 1 and 2, resulting from principal-component analysis (PCA) of five landscape attributes, with variations in color, from dark to light, corresponding to decreasing PC scores. (Bottom) Gray-scale map of management zones (MZ), resulting from unsupervised classification of PC scores for two PCs, with variations in color, from dark to light, corresponding to MZ 1 through 4.

View larger version (164K): [in a new window]   Fig. 3. Georeferenced soil-sampling scheme used to assess soil chemical properties at the Gibbon, NE, corn study site overlain on to the management zones (MZ) map. Variations in color, from dark to light, correspond to MZ 1 through 4.

View larger version (99K): [in a new window]   Fig. 4. Gray-scale yield maps of the 1997 through 2001 crop seasons from the Gibbon, NE, site. Variations in color, from dark to light, correspond to decreasing grain yields.

View larger version (17K): [in a new window]   Fig. 5. Semivariance analysis of yield spatial structure, showing variograms for the 1997 through 2001 years at the Gibbon, NE, corn study site.

View larger version (42K): [in a new window]   Fig. 6. Average grain yields of the four management zones (MZ), adjusted by yield spatial structure, for five crop seasons at Gibbon, NE, site. Standard error bars, adjusted by yield spatial structure, are shown to compare among yields of MZ within a given year.