SOIL ZINC MAP OF THE CONTERMINOUS USA USING GEOSTATISTICS AND GEOGRAPHIC INFORMATION SYSTEMS

Authors: WHITE, JEFFREY - CORNELL UNIVERSITY/SCAS; Welch, Ross; Norvell, Wendell

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Zinc is an essential element for all life. The soil is the primary source of zinc for plant, animal, and human nutrition. Zinc deficiency affects a variety of crops in many parts of the USA, but the geographic distribution of zinc in soils across the country is not well characterized. A map illustrating the zinc content of soils of the conterminous USA was developed using data from two previous studies. The spatial variability of the zinc content of soils sampled at numerous locations across the country was characterized using techniques known as geostatistics. This permitted estimation of the zinc content of soils between sampling sites, as well as a calculation of the certainity of these estimates. The estimates were entered into a geographic information system (GIS) to develop a color-coded map that shows how soil zinc varies from place to place. Soils north and west of New Mexico generally have greater than average zinc. Soils southeast of this boundary tend to have less zinc than average, with the exceptions of soils developed on Mississippi River deposits and in Piedmont valleys and ridges. The zinc map will contribute to the improvement and sustainability of agriculture and livestock production, to improvements in diet quality, and to a better understanding of the nature and extent of plant, human, and animal zinc deficiencies and related health problems. The map also will be useful in considering the consequences of land application of zinc-laden solid waste and sewage sludge. Previously, geostatistics had been used only at smaller scales. The geostatistical techniques used to map zinc will be useful in mapping the geographic distribution of other important micronutrients and toxic heavy metals in soils across the United States.

Technical Abstract: The geographic distribution of Zn in soils is important to agriculture, nutrition, and health. A map illustrating the geographic distribution of the total Zn content of soils of the conterminous USA was developed using geostatistics and geographic information systems. Soil Zn data came for two sources: a USGS survey targeting non-agricultural soils with scattered sampling in 47 states, and a USDA/USEPA/USFDA study targeting important agricultural soils in 33 states. Semivariogram analysis of the combined data indicated spatial correlation over a range between 330 and 470 km. Significant linear, quadratic, and cubic trends were modeled, but detrending had little effect on the semivariogram or on interpolation via kriging. The data exhibited some anisotropy which increased at longer lags, but this had little effect on kriging. An exponential semivariogram model was fit using a least squares algorithm, adjusted to obtain better fit at small lags, and used to interpolate, by kriging, a grid covering the conterminous USA. The resultant map depicted soils north of about 37 deg. N lat or west of about 109 deg. W long generally having more total Zn than the average of 55 mg kg-1. Soils southeast of this boundary tended to contain less Zn than average, with the exceptions of soils developed on Mississippi alluvium and in Piedmont valleys and ridges. High estimate standard deviations tended to occur where data were sparse. Geostatistics proved useful in characterizing the spatial variability of total soil Zn at the scale of the conterminous USA and in interpolating and mapping its geographic distribution.