Precision Agriculture Opportunities for Kentucky: Agronomic Research at UK

T.G. Mueller, R.I. Barnhisel, and S.A. Shearer

 © 2000, UK Dept of Agronomy Research Report, edited by Mike Barrett

Precision agriculture is about doing the right thing, at the right time, in the right place, in the right way.  Technologies employed include global positioning systems (GPS), yield monitors, geographic information systems (GIS), variable rate technologies (VRT), sensors (i.e. soil electrical conductivity), and remote sensing.  The goal is to use these technologies to make better soil use decisions and to optimize crop and soil management.  Precision agricultural management is not very different from traditional management approaches.  It is still about basing decisions on the best available crop and soil information which used to be field or farm yield or fertility averages.  But today with hi-tech tools, yield data are being collected every 15 ft or so and fertility samples are collected on 1 to 4 acre grids.  Precision agriculture technologies are a reality on farms in Kentucky, as many of our producers are already monitoring yields, and to a lesser extent conducting variable rate fertilization.  Unfortunately, there are few proven methods for using these technologies. 

A soil use decision is the first that a farmer makes for a field or area within a field.  Should this land be cropped?  If so, with what crop or crop rotation?  Certainly, traditional approaches (i.e. soil surveys) can be used successfully for aiding in decision making.  These approaches are based on the principle that soil limitations dictate appropriate soil uses, unless these limitations can be overcome through management practices.  Precision agriculture approaches are based on the same principle.  However, yield monitoring and GIS allow farmers to quantitatively compare the economics of one soil use decision to another.  Digital soil surveys can be overlain on yield maps to explain variability; however NRCS surveys may or may not be at the scale to explain much of the variability.  Agronomy researchers are working on a project to determine whether precision agriculture technologies (i.e. electrical conductivity sensors and elevation models) can be used to make intensive (first order) surveys more economically and more accurately.  Soil conductivity seams to be an important tool for making soil use decisions because it is related to topsoil depth and depth to bedrock.  There is a study underway to establish appropriate conductivity measurement protocol for Kentucky soils to explain the causes of soil conductivity variability and ultimately relate it to grain yield variability.  The use of precision agriculture tools for soil use decisions has the potential for improving farm profitability.  Another research project is designed to develop and evaluate statistical models for predicting soil properties across landscapes (depth of topsoil, soil organic carbon content, and clay content) as an alternative to grid based sampling or traditional soil survey techniques.  The ability to predict these variables accurately would be very useful.  For example, regions near the edges of fields or along slopes with little topsoil are often low yielding and unprofitable.  If these areas are removed from production, field profitability may improve.  Further, if these areas are enrolled in CRP, the whole field economics will improve even more.  Researchers in the Department of Agricultural Economics are developing economic decision aids that utilize yield maps for enrolling unproductive land into the conservation reserve program (CRP).  Better soil use decisions not only improve farm profitability, but they also benefit society as well.  Removing highly erodible land from production conserves water and soil by reducing erosion and runoff.  Adding buffer strips at field borders next to streams (riparian zones) reduces sediment, nutrient, bacterial and pesticide losses to streams.

Precision agriculture has the potential for improving the efficiency of crop and soil management.  If factors that limit productivity and profit can be identified within a field using soil sampling, digitized soils maps, or making field observations with GPS, then management steps such as site-specific tillage, variable rate nutrient management or seeding can be taken.  But before soils or crops can be managed, an assessment of their properties is required.  Faculty in the Department of Agronomy are conducting a study to determine if remote sensing can be used to predict forage quality.  An investigation is under way to determine how intensely fields must be grid-soil sampled in order to create accurate maps of soil properties using various interpolation procedures.  There are also studies to determine whether terrain attributes can be used to enhance the predictions of soil properties thereby improving the accuracy of grid sampling.  One study is being conducted to determine the ecological patterns with which perennial weeds are distributed across agricultural fields.  Understanding these patterns may help predict the probable location of perennial weeds in the future. 

After a particular soil or crop condition is known, there must be some basis for management.  There are studies being conducted to determine cause-effect relationships in the landscape.  What causes yield variability?  Is it landscape position, soil type, or chemical or physical properties?  The goal of one research project is to develop an efficient method for creating “management opportunity maps” indicating the factors that likely limit yield across agricultural fields.  These maps would be created with historical yield maps, soil sampling for fertility, and by making field observations using soil survey techniques.  If these causes are understood, then management steps can be taken to improve yields. 

Plant available soil water is one of the most important causes of yield variation in Kentucky soils.  It is affected by soil type and landscape position.  Site-specific irrigation is one way to manage soil water differences in agricultural fields, but unfortunately irrigation is not economical in most areas of Kentucky.  Another approach is to alter crop and soil management to match the soils ability to provide water to plants.  In drought prone areas, it may be a good idea to reduce seeding rates to conserve water.  Often, when water limits grain yield, other factors such as nitrogen will not limit plant growth (law of the limiting).  Therefore, it may be advantageous to back off nitrogen fertilizer rates on areas that tend to be droughty.  Several research projects involving Agronomy, Biosystems and Agricultural Engineering, and Agricultural Economics are evaluating the use of landscape position and soil type as a basis for variable rate seeding and nitrogen fertilization. 

There are approaches that could be used for fertilizer recommendations.  One approach may be to apply back to the field what has been removed during harvest.  A study is being conducted to determine if nutrient removal calculated from yield maps can be used as a basis for fertilization.  Another study is being conducted to determine if topographic position can be used to predict the need for starter fertilizer.  This relates to soil temperature and the kinetics of phosphorous diffusion in cold soils.  Another basis for fertilization is soil sampling either on grids or in zones.  There is an experiment being conducted to track the changes in soil fertility over time associated with variable rate fertilizer applications based on samples collected at various resolutions. 

One expectation is that precision agriculture technologies will improve environmental quality.  There is a study to evaluate impact of management practices on soil microbial diversity across Kentucky landscapes.  The idea is that some management practices may be more appropriate on some soils or landscape positions than others.

Much of the funding for this work is from two USDA grants that were earmarked for the University of Kentucky.  Other supporters include the Kentucky Corn Growers and the Kentucky Soybean Promotion Board.  While we have focused on agronomic research in this publication, it is important to recognize that precision agriculture problems are multifaceted and complex and therefore deserve an interdisciplinary research approach.  Our colleagues in the departments of Biosystems and Agricultural Engineering and Agricultural Economics are involved with many of our research projects but are also conducting their own precision agriculture research.

Table 1. Researchers at the University of Kentucky who are actively involved in precision agriculture research.

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