Topics in Agricultural Engineering: Precision Agriculture
Spring Semester 2007
Educational Module 9 Exercise: Variable-Rate Fertilizer Recommendations
The Cooperative Extension Service does not currently publish variable-rate lime and fertilizer recommendations for Kentucky. However, variable-rate lime and fertilizer application services are being provided to many Kentucky producers. If we assume that ARG-1 2002-2003 Lime and Fertilizer Recommendations are appropriate (the best available information) to guide producers in the development of variable-rate prescriptions, how should these recommendations be implemented in a GIS environment? In simple terms, how can we generate equations that continuously map soil test values to application rates?
The basis of the AGR-1 recommendations are described at the beginning of the publication as follows:
of a nutrient as a fertilizer are recommended based on a soil test result only
when a crop yield or economic response has been measured for that crop under
Kentucky soil-climatic conditions.
field studies have been conducted by the Kentucky Agricultural Experiment
Station under Kentucky farm conditions to determine the extent of any need for
nutrients (primary, secondary, and micro). Yield and soil test data from these
studies serve as guidelines in establishing recommendations in this publication.
contained in this publication are based on soil test values obtained from
testing methods used in laboratories operated as part of the Kentucky
Agricultural Experiment Station. Recommendations for phosphate, potash, and zinc
are based upon extraction by Mehlich III extract. Buffer pH is determined by a
modification of the SMP (Shoemaker, McLean, and Pratt) method. The Mehlich III
and SMP methods are described in Bulletin 190, Procedures Used by State Soil
Testing Laboratories in the Southern Region of the United States, Southern
Cooperative Series, November 1984. A detailed description of the soil test
procedures used in the UK Soils Testing Laboratory will be published in the UK
Agronomy Department's Agronomy Notes during 2000.
recommendations should not be used for soil test results obtained by other
testing methods. Recommended rates are based on assumed average climatic and
management conditions and average yields. Rates should be adjusted upward or
downward to reflect anticipated deviations from these average conditions.
rates recommended are for production of the crop to be grown each year and will
not increase soil test values for P and K rapidly. Using these recommended rates
would likely take four years or longer of annual fertilization to result in an
appreciably higher test level for P and K."
The objective of this
exercise is to use data from AGR-1 and software applications such as Excel and
MatLab to generate a set of equations that map soil fertility test results to
application rates for soil amendments. Specifically,
you are to develop a set of equations capable of generating application
prescriptions for phosphate and potash fertilizers along with a prescription for
the application of agricultural lime.
A copy will provided for completing this assignment.
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. 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. Agricultural lime 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 shape file format so that we can use them later in ArcGIS to generate profit maps.
Click on the file name to download the self-extracting executable file:
Excel File - Ag Lime
Field 41 Fertility Regions - Shape File
Field 41 Aerial Photo - DOQQ
State Roads - Tiger File