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Title: A RELATIVE-FLUX-CORRECTION SCHEME FOR ANALYZING THREE DIMENSIONAL DATA OF A TILE-DRAINED AGRICULTURAL PLOT

Author
item MOHANTY, B - U. C. RIVERSIDE
item KANWAR, R - IOWA STATE UNIVERSITY

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: When analysis of spatial data is important to understand the natural/induced heterogeneity in a soil profile, adaptive (site-specific) and knowledge-based approaches could help filter out any human-induced heterogeneity leaving natural heterogeneity for interpretation. In this study, using the subsurface-drain flow phenomenon, we developed a relative-Darcy-flux-based correction scheme to remove any tile-drainage-induced nonstationarity in the spatial data of soil nitrate concentration and soil moisture content prior to conducting the spatial analysis in the 3-D soil volume. Relative-flux-corrected data were analyzed for spatial structure in three principal (x, y, and z) directions. Linear spatial structures with strong anisotropy were discovered for relative-flux-corrected soil nitrate concentration and relative-flux- corrected soil moisture content. Furthermore, correlation between the two variables could be used for predicting the more expensive variable, (relative-flux-corrected) soil nitrate concentration, at unsampled locations using a cheaper surrogate, the measured (relative-flux-corrected) moisture content.

Technical Abstract: Soil water nitrate-nitrogen (NO3-N) concentration (mg/1) and soil moisture content (cm) data collected jointly from 175 sites arranged on a three-dimensional (3-D) grid network of a tile-drained agricultural plot were analyzed for their three-dimensional spatial distribution and for possible coregionalization. We propose a physical-process-based correction scheme to preprocess the nonstationary spatial data of soil NO3-N concentration and soil moisture content. Using the subsurface-drain flow phenomenon, we developed a relative-Darch-flux-based correction scheme to remove any tile-drainage-induced nonstationarity in the spatial data of soil NO3-N concentration and soil moisture content prior to conducting the spatial analysis in the 3-D soil volume. 3-D composite semivariograms of relative-flux-corrected NO3-N concentration and relative-flux-corrected moisture content showed anisotropic linear structures in three principal directions. Linear model characterized by steep slopes were found in the directions perpendicular to tile line as opposed to nugget models found in the direction parallel to the tile line. Good spatial correlation between the relative-flux-corrected NO3-N concentration and relative-flux-corrected soil moisture content and their anisotropic linear semivariograms produced anisotropic linear cross semivariograms in 3-D. The 3-D composite cross semivariogram will be useful in predicting the more expensive variable, (relative-flux- corrected) soil water NO3-N concentration, at unsampled locations in the soil profile with a cheaper surrogate, the measured (relative-flux- corrected) soil moisture content.