Spatial and Spectral Relationships of Soil Properties and Microtopography: I. Density and Thickness of A Horizon

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Abstract
The effects of microtopography and an intertill stratigraphic sandgravel layer on the spatial variability of A horizon thickness, density, and mass are examined using standard, spatial, and spectral statistical methods. Soil cores (76 mm diam) were taken every 1 m in a 46 m long transect, in a native soil which is a mixture of Typic Haploborolls and Typic Argiborolls. The parent material is glacial till divided into two formations. The uppermost till is 1 to 2 m thick and is underlain by an intertill seed‐gravel layer of variable thickness. Microtopography parameters were estimated by fitting a least squares quadratic surface to elevation measurements around each soil core. Spectral estimates (coherency, cospectrum, phase spectrum) are calculated using smoothed Fourier methods. Standard correlation indicated a significant relationship between surface curvature in the direction of maximum surface gradient and A horizon thickness and mass; however, only 14% of the variability was explained. Thickness and mass of the A horizon had significant autocorrelation and spectral peaks indicating spatial cycling. The power spectra of A horizon thickness and mass were very similar to that of surface curvature. Coherency and cospectrums indicated that relationships between variables are complicated by phase shifts and opposite correlations in different frequency ranges. This was attributed to lateral water movement in surface depressions and the presence of both open and closed depressions. A horizon properties were not significantly related to the depth to the intertill sand‐gravel layer.