Abstract
Soil texture varies significantly within many agricultural fields. The physical properties of soil, such as soil texture, have a direct effect on water holding capacity, cation exchange capacity, crop yield, production capability, and nitrogen (N) loss variations within a field. In short, mobile nutrients are used, lost, and stored differently as soil textures vary. A uniform application of N to varying soils results in a wide range of N availability to the crop. N applied in excess of crop usage results in a waste of the grower’s input expense, a potential negative effect on the environment, and in some crops a reduction of crop quality, yield, and harvestability. Inadequate N levels represent a lost opportunity for crop yield and profit. The global positioning system (GPS)-referenced mapping of bulk soil electrical conductivity (EC) has been shown to serve as an effective proxy for soil texture and other soil properties. Soils with a high clay content conduct more electricity than coarser textured soils, which results in higher EC values. This paper will describe the EC mapping process and provide case studies of site-specific N applications based on EC maps. Results of these case studies suggest that N can be managed site-specifically using a variety of management practices, including soil sampling, variable yield goals, and cropping history.
Highlights
Determining the proper amount of nitrogen (N) to be applied to an agricultural field is a source of debate and discussion among growers, input suppliers, and researchers
Some commonly accepted methods for devising N rates for corn, wheat, and cotton production are (1) the establishment of a yield goal that determines the overall N level needed for the crop to achieve that goal[1,2], (2) soil sampling to determine the ability of the soil to supply a portion of the N needed by the crop[2,3], and (3) local university research of N response functions
Devising a single N rate based on one yield goal for this field would likely result in overapplication to areas that have shown over time to have lower yield potential
Summary
Determining the proper amount of nitrogen (N) to be applied to an agricultural field is a source of debate and discussion among growers, input suppliers, and researchers. Devising a single N rate based on one yield goal for this field would likely result in overapplication to areas that have shown over time to have lower yield potential. Growers and their consultants can soil-sample and record georeferenced field characteristics with 1- to 3-m accuracy They are beginning to apply N based on subfield criteria, and varying rates to more closely meet the site-specific demands of the crop. These tools can be used in a site-specific manner to improve N efficiency by assisting in determining the availability of N in the soil and estimating the amount of N needed by the crop
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