BAE 599
Topics in Agricultural Engineering: Precision Agriculture
Spring Semester 2011

 Educational Module 4 Exercise: Variable-Rate Lime Application

Introduction

            In this exercise we will extend these relationships to an actual field situation, specifically Field 41 at the Worth and Dee Ellis Farm in Shelby County, Kentucky.  For comparison purposes you will be required to generate a shape file for use in variable-rate application.  This ".dbf" file should contain fields that specify application rates for agricultural lime (lb/ac).  The fertility management polygon has been developed (1-acre grid) and can be downloaded below.  This will form the basis for the development of the application shape file.

            In addition to generating the variable-rate application shape file you should do a comparison of variable-rate versus "field-average" management using AGR-1 recommendations.  The comparison should include specification of the total quantities of lime to be applied under either approach.

Project Requirements

1. Download and expand the shape files for Field 41 as demonstrated in class.  Using these shape files generate a project in ArcMAP named Field 41.
2. Open the table associated with the fertility regions shape file for editing.  Add fields for lime, phosphate (DAP), and potash application rates.  Be certain to specify the data type for the new fields as "numerical."  Save the edited changes and export the shape file.
3. Open Excel and bring in the ".dbf" file associate with the Field 41 fertility regions file.  Using the relationships generated in Exercise 5, specify the application rates for the soil amendment for each polygon.  When finished save the edited file once as an Excel file and again as a ".dbf" file.  Saving the spreadsheet as a ".dbf" file preserves only the data in each cell, not the associated equations.
4. Open ArcMAP and bring the edited shape file back into the Field 41 project.  You should now be able to view the table and see the recommended application rates.  Using the new file generate and print application maps for agricultural lime.  Be certain to change the key to reflect varying levels of application.
5. Using the Excel version of the edited ".dbf" file determine the total quantities of agricultural lime to be applied in Field 41 under both field-average and variable-rate management approaches.  Please not that one of the field contains the area of each polygon.
6. For this project you will be require to submit hard-copies of the three application rate maps, and your answers to the questions below.  Also, e-mail the instructor a copy of the Excel spreadsheet used to determine the application rates and total quantities of fertilizer to be applied using the variable-rate application approach.  

Questions

1.  How does the total quantity of applied agricultural lime differ between the variable-rate versus field-average management approaches?
2. Is it appropriate to use a one-acre sampling grid for specification of variable-rate application prescriptions?  Remember Dr. Mueller's presentation on map accuracy?
3. If you were to redefine the fertility management grid, what changes would you make?
4. If the cost of grid sampling is $8.00 per sample, once every four years, and variable-rate application costs an extra $3.50 per acre per product applied, would you spend the time and effort to manage this field using variable-rate technology (VRT)?  Why or why not?

Additional Information

        The soil sample results from Field 41 at Worth and Dee Ellis Farms in Shelby County, Kentucky are zipped and included below.  This data was obtained by grid sampling the field and submitting the samples to Regulatory Services at the University of Kentucky.  Mehlich III extraction methods were used to arrive at the soil test values for P and K.  Using the soil test data, and the University of Kentucky’s AGR-1 Extension Publication on soil fertility, determine the total cost of lime input for variable-rate application.  Assume this year’s crop will be corn, and the preceding crop was wheat followed by double-cropped soybeans.  The management grid is composed of 1.0-acre cells.  Assume that each sample corresponds to a single complete cell.  Agricultural lime will be used to adjust the soil pH and is valued at $13.00 per ton.  Please show all work used to arrive at the total cost of inputs under either scenario.  Save your fertility recommendations in a “.dbf” format so that we can use them later in ArcMAP to generate profit maps.