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United States Department of Agriculture

Agricultural Research Service

Title: Feasibility of Site-Specific Management of Corn Hybrids and Plant Densities in the Great Plains

Authors
item Shanahan, John
item Doerge, Thomas - PIONEER HB IOWA
item Johnson, Jerry - COLO ST UNIV COLO
item VIGIL, MERLE

Submitted to: Precision Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 2003
Publication Date: June 4, 2004
Citation: Shanahan, J. F., Doerge, T.A., Johnson, J. J., and Vigil M.F. 2004. Feasibility of site-specific management of corn hybrids and plant densities in the Great Plains. Journal of Precision Agriculture 5:207-225.

Interpretive Summary: Modern farmers are keenly aware of the productivity differences in their fields, and recognize the potential value of using site-specific management versus uniform application rates in managing crop production inputs. Images depicting highly variable crop growth within fields are often used to advance the intuitive appeal of variable rate farming. However, only manageable and predictable sources of within-field variation can be exploited to cover the cost of variable rate application. Seeding different crop varieties on the go at variable planting densities is technologically feasible. Precision farming pioneers have predicted that crop variety will be the second most important input for site-specific management. Crop variety is an ideal subject input for precision farming because yield variation due to variety selection is ultimately manageable, i.e. plant the optimum variety in different parts of the field. While previous research observed differences in optimal plant densities as a function of yield potential in an extensive study in the Corn Belt region of the U.S, the researchers concluded that variable rate seeding would be infeasible, because of the high cost associated with characterizing site variability. However, in the western Great Plains region of the U.S., where annual precipitation averages only 350-432 mm, drought stress is a more limiting factor. Research for this region indicates that optimal planting densities and hybrid selection (short- vs. long - growing season) for dryland production are highly dependent on available seasonal water, with lower planting densities and shorter season hybrids recommended for conditions with reduced available seasonal water. Thus, we hypothesized that the optimal combination of hybrid maturity (short vs. long) and plant densities (low vs. high) would change according to variation in yield potential across the landscape, and variation in yield potential may be related to change in topographic and soil quality features which affect available soil water and crop growth. The goal of this research was to estimate potential for use of site-specific management of corn hybrids and plant densities for dryland landscapes in the Great Plains by determining 1) within-field yield variation, 2) yield response of different hybrids and plant densities to variability, and 3) landscape attributes associated with yield variation. This work was conducted on three adjacent fields in eastern Colorado during the 1997, -98, and -99 seasons. Our experimental treatments consisted of a combination of two corn hybrids (early and late maturity) and four plant densities (24692, 37037, 49382and 61727 plant per hectare) seeded in long strips and replicated. At maturity, grain yield was measured with a commercial combine equipped with a grain yield monitor and global positioning system (GPS) to map yield across the field. Nine landscape attributes including elevation (with GPS), slope (from elevation data), soil brightness (with red, green, and blue bands of aerial photograph of bare soil), soil electrical conductivity (with commercially available soil electrical conductivity mapping device), soil pH, and SOM were also assessed. Grains yield and landscape attribute data were viewed and analyzed in a commercially available geographical information systems (GIS) software package. A statistical analysis of treatment yields and landscape data was used to determine associations between yields and landscape attributes. Yield monitor data revealed considerable variability in the three fields, with yields ranging from 5.43 to 6.39 Mega grams per hectare and coefficients of variability ranging from 20 to 29%. Hybrids responded similarly to field variation while planting densities responded differentially. Economically optimum plant densities changed by around 5000 plants hectare between high and

Technical Abstract: The goal of this research was to estimate potential for use of site-specific management of corn hybrids and plant densities for dryland landscapes in the Great Plains by determining 1) within-field yield variation, 2) yield response of different hybrids and plant densities to variability, and 3) landscape attributes associated with yield variation. This work was conducted on three adjacent fields in eastern Colorado during the 1997, -98, and -99 seasons. Treatments consisted of a combination of two hybrids (early and late maturity) and four plant densities (24692, 37037, 49382and 61727 pl. ha-1 ) seeded in long strips and replicated. At maturity, yield was measured with a yield-mapping combine. Nine landscape attributes including elevation, slope, soil brightness (red, green, and blue bands of image), ECa (shallow and deep readings), pH, and SOM were also assessed. An analysis of treatment yields and landscape data, to assess for spatial dependency, along with semi variance analysis, and block kriging were used to produce kriged layers (10 m grids). Linear correlation and multiple linear regression analysis were used to determine associations between kriged average yields and landscape attributes. Yield monitor data revealed considerable variability in the three fields, with yields ranging from 5.43 to 6.39 Mg ha-1 and C.V.'s ranging from 20 to 29%. Hybrids responded similarly to field variation while planting densities responded differentially. Economically optimum plant densities changed by around 5000 plants ha-1 between high and low-yielding field areas, producing a potential savings in seed costs of $6.25 ha-1. Variability in yield across the three landscapes appeared to be highly associated with the measured landscape attributes, particularly elevation and soil brightness. Various combinations of the landscape attributes accounted for 47, 95, and 76% of the spatial variation in average grain yields for the 1997, -98, and -99 sites, respectively. Our results suggest site-specific management of plant densities may be feasible.

Last Modified: 9/29/2014