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Estimates of Soil Nitrate Distributions Using Cokriging with Pseudo-Crossvariograms

Dep. of Renewable Resources, Univ. of Wyoming, Laramie, WY 82071-3354;

Pete Shouse and Scott Yates

U.S. Salinity Lab., USDA-ARS, Riverside, CA 92507-4617.

^* Corresponding author (renduo{at}uwyo.edu)

ABSTRACT

Nitrate (NO^–₃) is one of the major nonpoint source pollutants in the vadose zone. In this study, NO^–₃ distributions were estimated in an 800 by 800 by 1.8 m soil volume using kriging and cokriging with nonsymmetric pseudo-crossvariograms. Cokriging with pseudo-crossvariograms maximized the use of available information at different soil depths. Cokriging allowed easily obtained information at shallow layers to be used to improve soil chemical estimations at deeper layers. Compared with kriging, cokriging significantly reduced the mean squared errors (MSEs) and mean kriging variances (MKVs) of NO^–₃ estimations in the soil. For the same estimation accuracy of kriging, cokriging with pseudo-crossvariograms used less than half the data; thus potentially it could reduce more than half the sampling cost than kriging estimation. Cokriging with pseudo-crossvariograms was shown to be a precise and an economic way for determining nonpoint source pollutant distributions in large fields.