Soil zinc map of the USA using geostatistics and geographic information systems

The geographic distribution of soil Zn is important to agriculture, nutrition, and health. A map illustrating the total Zn content of soils of the conterminous USA was developed using geostatistics and geographic information systems. Data were combined from a U.S. Geological Survey study targeting nonagricultural soils in 47 states, and a U.S. Department of Agriculture-U.S. Environmental Protection Agency-U.S. Food and Drug Administration study targeting agricultural soils in 33 states. Semivariograms indicated spatial correlation at distances up to 470 km. A significant quadratic trend was modeled, but detrending had little effect on the semivariogram or on interpolation via kriging. The data exhibited some anisotropy, but it had little effect on kriging. An exponential semivariogram model was fit using least squares and used to krige a grid covering the conterminous USA. The resultant map depicted soils north of about 37 degrees N latitude or west of about 109 degrees W longitude as generally having more Zn than the average of 55 mg kg-1. Soils southeast of this boundary tended to contain less Zn than average, with exceptions of soils developed on Mississippi alluvium and in Piedmont valleys and ridges. High estimate standard deviations occurred where data were sparse. The map will be useful in future research to determine the geographic distribution of plant-available soil Zn, regional patterns of plant, animal, and human Zn deficiencies, the relationship of Zn to soil parent material, genesis, and surficial geology, and in considering the consequences of land disposal of Zn-laden wastes