Variability and Scale: Considerations for Precision Agriculture

November 27, 2017
By Karen Hills

It is human nature to be entranced by the latest electronic gadget that promises to make our lives easier. Sometimes gadgets really do help us, and other times this help is counterbalanced by the hours spent trying to troubleshoot when things go wrong. Because I’m not really a “gadget person” by nature, I must admit that I hadn’t paid a whole lot of attention to precision agriculture during my time working in the world of agricultural research. However, I recently had the opportunity to learn more about this topic while helping to compile and edit the book Advances in Dryland Farming in the Inland Pacific Northwest. By reading the chapter on Precision Agriculture co-authored by Bertie Weddell, Tabitha Brown, and Kristi Borrelli, I learned about two of the most important factors to consider when it comes to the use of precision agriculture technology: variability and scale.

Variability is key

Precision agriculture is the use of technology to manage farm and field variability to improve outcomes such as yield, grain quality, and fertilizer use efficiency. The benefits of using precision agriculture technology come from being able to manage crops in a way that precisely matches the needs of a specific area. Precision agriculture technology can be used to vary applications of fertilizer, herbicide, or manure, as well as to adjust seeding rate. However, the input most often discussed in precision agriculture is nitrogen fertilizer. This is because nitrogen is typically the limiting nutrient in crop production; it represents a substantial cost to producers; and it can be easily move from the field in soluble or gaseous forms.

Ideally, nitrogen is applied at a rate that maximizes crop yield, while minimizing fertilizer over-application which can be costly and have environmental consequences. This ideal amount of nitrogen can vary significantly, even within a single field. For example, on hill slopes there is generally less topsoil, less stored water, and lower yield potential than in flatter upland areas of a field (Figure 1). When a single rate of nitrogen is applied across the whole field, this typically results in over-application on hill slopes and under-application on relatively flat upland areas. This is where precision agriculture comes in. By using two different nitrogen application rates on hard red spring wheat, Huggins (2010) increased yield in both high and low yielding areas, by 12% in the high yielding areas and 25% in the low yielding areas.

Figure 1. Field elevation, slope, and combine yield monitor data for hard red spring wheat at a farm near Colfax, Washington. (Dem = digital elevation model; Source: Weddell et al. 2017)

Scale matters

As described by Weddell and her co-authors, there are two different steps in precision agriculture: the measurement of field variability and the translation of that variability into a site-specific management plan. Examples of field variability measurements including elevation, slope, and yield are shown in Figure 1. Other measurements that may be used include soil organic matter, soil moisture, or nutrient levels. Weddell and her co-authors emphasize that the scale at which field variability is mapped should be dictated by the application technology that will be used. For example, if you have the ability to vary application rate on a scale of meters, then mapping field variability down to a scale of feet would not provide any added benefit and would be inefficient.

Translating in-field variability into a specific plan for how to vary management by zones is the most complicated step in the process. Often precision agriculture consultants are hired to help create a management plan based on in-field variability. Finally, an important part of the process is reevaluating management decisions based on the yield or quality data collected during harvest, and adjusting next year’s plan as needed.

Before working on Advances, I had not appreciated that precision agriculture technology comes in many different forms, so producers adopting this technology do not have to take an “all or nothing” approach. The more intense versions involve use of decision-making software and consultants. On the simpler side is the auto-steer using a differential Global Positioning System (GPS), which is commonly used in the inland Pacific Northwest to prevent overlapping passes during planting or application of herbicide or fertilizer. As impressive as the technology is, it should not be forgotten that grower knowledge is still critically important, along with the data from information technologies, in influencing management decisions.

Dr. Tabitha Brown of USDA-ARS and Washington State University & Dr. Erin Brooks of the University of Idaho

More information on precision agriculture technology, including descriptions of tools and equipment available, steps for implementing variable nitrogen rate application, and sources of decision-making support, can be found in the Precision Agriculture chapter in Advances. Or to hear the highlights as well as producer and industry perspectives on precision agriculture, tune in to the upcoming webinar Nutrient Management and Precision Application Technology on Monday December 4 8:00-9:00 a.m., PST.






Huggins, D. 2010. Site-Specific N Management for Direct-Seed Cropping Systems. In Climate Friendly Farming: Improving the Carbon Footprint of Agriculture in the Pacific Northwest, Kruger et al., eds. CSANR Research Report 2010-001. Pullman: Washington State University.

Weddell, B., T. Brown, and K. Borrelli. 2017. Precision Agriculture in G. Yorgey and C. Kruger (Eds.) Advances in Dryland Farming in the Inland Pacific Northwest. (p. 319-352). Pullman WA: Washington State University Extension.


A full set of references for the information presented is available in Precision Agriculture in Advances in Dryland Farming in the Inland Pacific Northwest.

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