Abstract
The spatial variability of soil texture and soil nitrateN, P, and K was studied in two centerpivot irrigated fields(89 ha total). Two soil texture components (clay and silt) were found to be correlated with soil nitrateN, P, and K, and wereused as auxiliary variables in the cokriging procedure to estimate soil nitrateN, P, and K at unsampled locations. With asampling density of 2.7 sites/ha (61 . 61 m grid) as the baseline, removal of 50% of the sampling sites resulted in a normalizedmean absolute error (NMAE) of 34.5%, 22.9%, and 15.3% for soil nitrateN, P, and K, respectively. These numbers reducedto 32.8%, 20.7%, and 12.0% when only 25% of the sampling sites were removed. The study showed that the cokrigingtechnique provided slightly better estimates than the ordinary kriging method for soil P and K at a higher sampling density(>2.1 sites/ha). However, when a variable has a large random variation, such as the soil nitrateN, cokriging did not providebetter estimates than ordinary kriging. The results of this study provide guidelines on the selection of kriging or cokrigingin improving the soil nutrient sampling efficiency.
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