Spatial Variability of Measured Soil Properties across Site-Specific Management Zones

homogeneous yield-limiting factors, for which a single rate of a specific crop input is appropriate (Doerge, 1999). The spatial variation of productivity across farm fields can be classiVarious techniques of delineating management zones fied by delineating site-specific management zones. Since productivity are currently being investigated in different parts of the is influenced by soil characteristics, the spatial pattern of productivity USA (Fraisse et al., 1999; Fleming et al., 2000; Khosla et could be caused by a corresponding variation in certain soil properties. al., 2002; Fleming et al., 2004). Site-specific management Determining the source of variation in productivity can help achieve more effective site-specific management. The objectives of this study zones as described by Fleming et al. (2000) and Khosla were (i) to characterize the spatial variability of soil physical properties et al. (2002) were delineated from the variability in color across irrigated corn (Zea Mays L.) production fields and (ii) to observed in bare soil imagery of conventionally tilled determine if soil physical properties could explain the variability in field, farmer’s perception of field topography, and farmproductivity between site-specific management zones. The study was er’s knowledge of past production practices. The variconducted over three study sites in northeastern Colorado. The soil ability in bare soil reflectance, and that observed by the properties measured were bulk density, cone index, surface soil color, farmer, is due, in part, to non-uniform distribution of organic C, texture, sorptivity, and surface water content. A multicertain soil properties that influence crop productivity. response permutation procedure was used to test for significant differVariability in soil properties is a direct result of the five ences among soil properties between management zones. Box plots soil forming factors: climate, organisms, relief, parent of soil physical properties were created for each management zone material, and time (Jenny, 1941). within each study site to determine if trends in soil physical properties Of the five soil forming factors, relief (topography) corresponded to the productivity potential of the management zones. Overall, this study showed that soil physical properties exhibited sigcan be most readily assessed. Changes in field topogranificant spatial variability across production fields. The trends obphy influence the distribution of soil properties and crop served for the measured soil physical properties corresponded to the productivity across a field. Multi-fold variations in crop productivity potential of the management zones. Utilizing site-specific yields within a field have been reported in several studmanagement zones could help manage the in-field variability of yieldies. Crop yields ranged from 1.0 to 6.7 Mg ha 1 in a field limiting soil physical properties. in east-central Alberta, Canada (Goddard and Grant, 2001). Low, medium, and high organic matter zones were found to correspond with top, middle, and bottom S studies have documented that soil properslope landscape positions (Mulla and Bhatti, 1997). ties vary across farm fields, causing spatial variabilThey also reported increasing grain yields with increasity in crop yields (Rockström et al., 1999; Gaston et al., ing soil organic matter content. 2001). Precision farming or site-specific management is Spatial variability in soil physical properties, nutrient aimed at managing soil spatial variability by applying levels, and water content has been well documented inputs in accordance with the site-specific requirements (Fulton et al., 1996; Chung et al., 2001; Gaston et al., of a specific soil and crop (Fraisse et al., 1999). Such 2001). Chung et al. (2001) found that grain yield, electrimanagement practices require quantification of soil spacal conductivity, Ca, K, Mg, Na, and SiO2 can exhibit tial variability across the field. One of the recent apsignificant and large-scale variability within a relatively proaches to quantify soil spatial variability for site-spesmall area of relatively low topographic relief (i.e., 3 ha). cific management is to divide fields into productivity level Soil compaction and bulk density have also been documanagement zones (Khosla et al., 2002; Fleming et al., mented as varying significantly within single fields (Fulton et al., 1996; Wells et al., 2000). Spatial variability in 2000). A management zone is a subregion of a field with certain soil parameters can have influence on the spatial distribution of crop productivity potential. Variability in M. Mzuku, Lecturer, Dep. of Agricultural Engineering and Landuse clay and soil organic C was shown to exert influence on Planning, Private Bag 0027, Botswana College of Agriculture, Gaborthe location and density of weeds (Gaston et al., 2001). one, Botswana; R. Khosla, Associate Professor, Dep. of Soil and Crop Inman et al. (2005) reported that fields that have a high Sciences, Colorado State Univ., Fort Collins, CO 80523-1170; D. Inman, Research Associate, Dep. of Soil and Crop Sciences, Colorado State degree of spatial variability in soil properties could be Univ., Fort Collins, CO 80523-1170; R. Reich, Professor, Dep. of Forest, better managed using site-specific management zones. Range, and Watershed Stewardship, Colorado State Univ., Fort Collins, Review of the literature indicates that most previous CO 80523. F. Smith, Professor, Dep. of Forest, Range, and Watershed investigations have focused on the study of spatial variStewardship, Colorado State Univ., Fort Collins, CO 80523; L. Macability caused by a particular soil property, that is, comDonald, Professor, Dep. of Forest, Range, and Watershed Stewardship, Colorado State Univ., Fort Collins, CO 80523. Received 27 Feb. paction, texture, soil organic C, etc. (Fulton et al., 1996; 2005. *Corresponding author ([email protected]). Wells et al., 2000; Gaston et al., 2001). Classifying fields into different levels of productivity management zones Published in Soil Sci. Soc. Am. J. 69:1572–1579 (2005). Soil Fertility & Plant Nutrition doi:10.2136/sssaj2005.0062 Abbreviations: DGPS, differentially corrected global positioning system; GIS, geographic information system; GPS, global positioning © Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA system.