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Managing In-field Variability
Site-Specific Nutrient Management
Site-Specific Insect Management
Site-Specific Weed Management
Site-Specific Irrigation Management
Site-Specific Soil Sampling
Site-Specific Farming Enhances Farm Resilience
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Managing Variability on Your Farm

Managing In-field Variability

Today we live in the age of information technology and agricultural operations are no exception to the explosion in technology. Crop production variability in farmers' fields has been an age-old problem and modern agriculture stills faces the challenges of managing this variability. There are a number of commercially available technological “tools” in the market to manage in-field variability. Before we proceed further, lets understand what we mean by variability, the types of variability, tools to measure field variability, scale of variability, and finally managing variability.

The term “soil or crop variability” refers to the changes in soil or crop properties across a field. Examples of soil variability could be changes in soil pH, soil texture, soil type, soil organic matter, water holding capacity, or other soil properties, as you go from one part of the field to another. Examples of crop variability could be changes in crop growth and development, crop vigor, crop yield, crop height, or other crop parameters, as you go across the field. This change that occurs across space (distance) is referred to as “spatial variability”. There is another type of variability that is called “temporal variability” which means variability associated with time. For example, each year yields across the field vary significantly as impacted by weather, pests, etc.; this variation in yield variability across years is referred to as temporal variability.

Variable rate application of nutrients in a farm field.

There are various tools and techniques available for measuring in-field variability. Some of these tools and techniques include: (1) Grid-based soil sampling, in which a field is divided into small grid cells 1 acre or more in size and then soil samples are collected from each grid cell. This allows us to measure the variability associated with soil properties. (2) Yield monitor is a tool, which measures the variability in crop yield across the field. However, variability in yields across a field could be because of a number of reasons. A yield monitor simply quantifies the yield variability. It takes quite a bit of “detective work” to determine the reasons associated with variability in crop yields. [Read a detailed article on yield monitoring and yield monitor sensors in our extension newsletter of November 2002 “Sensors in Agriculture”] (3) Remote sensing of fields with or without a crop also helps quantify variability associated with soil and crop properties. An image of a standing crop acquired through a camera on an airplane or a satellite allows you to identify areas of crop stress or distribution of weed populations, or non-uniform planting areas, etc., across a field. (4) Soil electrical conductivity mapping is a fairly new tool that helps quantify variability associated with soil properties. Numerous uses of soil electrical conductivity maps are being developed every year. An article in this newsletter provides the findings of utilizing soil electrical conductivity maps for variable rate pre-emergence herbicide applications. [Read a detailed article on soil electrical conductivity in our extension newsletter of November 2002 “Sensors in Agriculture”] Over the last 5 years in Colorado, we have mapped variability of several farm fields in the Front Range, Northeastern Colorado, Southeastern Colorado, and the San Luis Valley areas. All the fields that were mapped showed variability in soil and crop properties. However, these results should be interpreted with caution. Prior to making any management decision, one should be cognizant of the “scale of variability” associated with a particular soil and crop property. For example, in corn fields we have found that the computer may show a grain yield map that “appears” highly variable across the field. However, a closer look at the “scale of variability” may show that the grain yields varied only from 180 bushels/acre to 210 bushels/acre. Such a small-scale of variability, i.e., 30 bushels/acre across the whole field may not constitute a good enough reason for that field being a good candidate for variable rate management. In addition to the “scale of variability” another important aspect in making a management decision is the reason of the variability. Understanding the reason associated with variability is equally important to determining whether or not the variability can be managed.

Managing variability is the final step in the process of site-specific farming. Once you know how much variability exists in your field, what type of variability it is, and whether or not you can manage it to improve production, the next logical step is to manage that soil and/or crop variability via variable rate input management. There is a perception that variable rate management of soil and crop variability minimizes variability across the field. This is incorrect. Variable rate management of agricultural inputs (nutrients, irrigation, herbicide, seeding, etc.), allows you to maximize the efficiency of farm inputs and thereby minimize the variability in net $ return from across the field.

The overall concept of site-specific management is application of farm inputs at the right time, in the right amount, and at the right place. This issue of the newsletter provides an insight into managing variability in fields. Articles were invited from specialists around the country (North Dakota, Georgia, Texas and Colorado). Hopefully, it will provide you with new production information and stimulate some thoughts as to how you can manage and take advantage of variability that exists in your fields.

For specific question, please do not hesitate to contact me.

Thank you,
Dr. Raj Khosla
Precision Agriculture Specialist
Colorado State University

FROM THE GROUND UP agronomy news is a monthly publication of Cooperative Extension, Department of Soil & Crop Sciences, Colorado State University, Fort Collins, Colorado.

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The information in this newsletter is not copyrighted and may be distributed freely. Please give the original author the appropriate credit for their work.

Raj Khosla,
Technical Editor

Direct questions and comments to:
Deborah Fields
Phone: 970- 491-6201
Fax: 970-491-2758
Extension staff members are:

Troy Bauder
, Water Quality
Mark Brick, Bean Production
Joe Brummer, Forages
Betsy Buffington, Pesticide
Pat Byrne, Biotechnology
Jessica Davis, Soils

Jerry Johnson, Variety Testing
Raj Khosla, Precision Farming
Sandra McDonald, Pesticide
Calvin Pearson, New Crops
James Self, Soil, Water & Plant Testing
Reagan Waskom, Water Resources

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Colorado State University, U.S. Department of Agriculture, and Colorado counties cooperating. Cooperative Extension programs are available to all without discrimination. The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by Colorado State University Cooperative Extension is implied.
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