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Fluid Journal : Fluid Journal 1996-1998
3 Fluid Journal Spring 1996 central Nebraska, an organic map (>2000 samples) generated by sampling on an alternate 40- by 80-foot grid (0.073 acre) closely resembled the photograph of bare soil color. Systematically removing v sampling points from data in the above example resulted in a series of organic matter maps representing progressively coarser grids. Comparison of these maps showed distinctly different patterns as grid spacing increased, raising concern about the common grid sampling strategy that uses a 450-foot grid. Intensive grid sampling such a field for available P resulted in a map that resembled both the bare soil color photograph and organic matter map, with an exception of high values in the area of an old farmstead and associated livestock operation. Based on its average Bray P concentration of 13 ppm, this field would be expected to show a slight to moderate P response. The grid map showed that 74 percent of the field should respond to P. Consultants typically use a higher critical level because they recognize the likelihood of spatial variability in fields and the need to meet plant nutrient needs. Fertilizer recommendations generated from such plot data do not incorporate a scaling factor that includes the reality of spatial variability. A critical level of 24 ppm in the above scenario indicated 87 percent of the field would be expected to respond to P. Systematically removing data points to increase grid size generated a sequence of P maps that showed a number of inaccuracies when using a 240-foot grid. These examples suggest that aerial photography of bare soil can be a useful tool to help make more intelligent soil sampling decisions that are environmentally friendly. Photographs taken during the growing season can be a powerful tool to identify spatial variability in crop growth. Looking ahead Ultimately, on-the-go crop sensors under development for high-clearance vehicles or mobile irrigation systems may be able to detect certain crop stresses and permit real-time correction measures. This could be accomplished without aid of GPS technology and perhaps remove a level of intimidation associated with some aspects of precision management. Equally viable may be the use of aircraft or satellite images to identify problem areas in fields and use of available technology to control ON- OFF or variable rate applications of nutrients, pesticides, etc. While the concept of site-specific management offers many possibilities, time will tell if the intuitive benefits of variable rate application technology and site-specific management translate into environmental stewardship and producer profitability. Dr. Schepers is a soil scientist with the USDA -ARS. and adjunct professor University of Nebraska, Lincoln, Nebraska.
Fluid Journal 1993-1995
Fluid Journal 1999-2001