Can The Web Soil Survey Help To Uncover Answers To Precision Farming Questions?

Can The Web Soil Survey Help To Uncover Answers To Precision Farming Questions?

A farming magazine recently published an article of an interview of two experts discussing how understanding the topography of a field can assist farmers in understanding soils. The first paragraph began with the sentences:


“For decades, NRCS soil maps have been a great way to detect soil types in a field. There’s a new generation of technologies and maps, though, that better decipher those differences and the way soils function.”

The SCS/NRCS soil survey provides information on soil mapping units. The historical manuscripts explained the major named components and described the inclusions found in the map units. Today’s NRCS digital soils maps and the associated database have evolved from the historical printed copy manuscripts. The historical manuscript provided descriptions of the map units, the taxonomic units, and the county soils maps. Recent updates to the Web Soil Survey (WSS) database provide more details on all soil components, their soil properties, and their locations within the map unit. The database contains a great deal more information than most users realize.

The article continued:

“We are lucky to have had NRCS maps and understand them as we have.” … “But in precision farming, we are ready to go to the next step.”

The NRCS maps that were directed by Congress over 100 years ago to create an inventory of arable lands evolved into a soils inventory designed for broad land use planning. In recent decades, the digital product has been improving, maybe not to the specific scale for precision farming, but it has been improved to add more information on the soils within the map unit. The paragraph continued:

“NRCS soil maps delineate soil types via boundary lines. In reality, changes between soil types in a field are gradual and don’t stop and start on a line….”.

The term “soil type’’ referred to in the article is a misnomer and displays the lack of clear understanding. The soil maps delineate a “map unit”. The “boundary lines” delineate a map unit and that map unit, typically, contains more than one type of soil. This misuse of terminology by the article’s authors and on precision farming web sites should be clarified. Recent work with precision farming agronomic firms have shown that many agronomists are not fully aware of the soil survey. Those using the term “soil type” are not aware of breadth and depth of the NRCS Web Soil Survey database.

The farmer has many tools available to answer questions.  Yield monitor maps are one of the most useful tools in precision farming.  The soil survey map is delineated by map units, however yield monitor maps can help associate the map unit soil components.  Compare any Web Soil Survey soils map to a yield monitor image. Carefully consider the image signatures. You will notice the crop yield monitor has specific red areas designating lower production.  Compare the images and notice the correlation of the yield monitor red areas and how the correspond to the various tonal photographic image areas. In the soil survey image below, the areas of lower crop yields fall within a map unit 11 in the white toned image areas.  Unfortunately, the article’s authors described these polygons with their variabilities as one soil type. The question becomes, “How can the ‘Web Soil Survey’ be used to explain the diversity of soils within the polygons?”

Web Soil Survey soils map

Web Soil Survey soil map.

Precision farming has many potential inputs available to develop a farming prescription. The Web Soil Survey map, the crop yield monitoring map, maybe using Veris Technologies mapping, or EC mapping, drone imagery for crop scouting, elevation analysis, or even soil moisture monitoring. All of these can be used to build a precision farming prescriptive analysis. But that prescription has soil as its foundation. The value of the Web Soil Survey map is to make informed decisions based on the many soil types within each map unit. The value is also to understand the soil properties associated with each soil type in the map unit. Using the variety of inputs assists the farmer in understanding the multiple soil components within the map unit and how each soil impacts the overall crop production.

The Web Soil Survey soil map above identifies three map units that exist in this field.


Web Soil Survey users, and even soils experts, tend to assume there is only one soil component, or soil type, within the boundary lines. Further investigation recognizes there are a number of soil components in the map unit. Consider map unit 11 in the soil survey map above. This soil type has five soil components identified in the database. Unfortunately, most users consider only the first soil, in this case the “Colby”. Note the list of soil components, their cover kinds, slopes, and erosion classes below:

List of soil components

Aggregating the Colby component makes this soil type the vast majority of the map unit (95%). However, the second Colby is eroded and makes up 20% of map unit 11 (white areas on the image). Each of these five soil components (Colby, Colby eroded, Ulysses, Goshen, and Pleasant) have their own unique set of soil properties. The Colby component has the eroded phase separated to properly define its unique set of properties as it exists in the map unit.

The Web Soil Survey reports provide information on the soil horizons and the horizon properties. Note the soil horizons and soil properties for the non-eroded Colby component:

Soil horizons and soil properties

The Colby soil is a young soil formed in windblown sediments and has very little soil development. Contrast the Colby non-eroded soil properties to the Colby eroded soil properties as detailed in the same map unit. Notice how the erosion of the surface horizon exposes the high carbonate loess materials containing lower organic matter and higher carbonate contents, both which negatively affect crop productivity. Compare the horizons of the non-eroded Colby soil (75%) to the eroded Colby (20%). Consider the Colby soil type and the importance of understanding the productivity between the Colby component and the Colby eroded component.

The article continues:

“There is a strong correlation,” … “Within a field, you might see a general trend between soil type boundaries and actual field topography, but it will not line up perfectly.”

The soil scientist made every attempt to draw the line as accurately as possible. Using a landscape model, the soil scientist identified the minor components and their locations as they occur within the map unit. In the map unit 11 instance, the Colby eroded unit is located on the crest or knoll, whereas the non-eroded Colby component occurs on the side slopes and more level areas within the map unit. The WSS contains reports the user can run to identify the components and their locations within the map unit polygon boundaries.

“You can extract lots of information from maps like these.”…. “Let’s say you get a 2-inch rain in an hour on a field that is dish-shape. There will be tops of the hills that get an inch and lower parts that get 3 inches of rain. This might make a difference in the hybrid you plant or the field’s nitrogen management. It can go into a prediction model to predict how to better target inputs the next time.”

The expert’s statement eluded to the use of “functional maps” and algorithms to identify how soils may be different based on the topological location in the field. Using the Web Soil Survey reports allows the user to confirm the soil, its location, and its’ properties that aid in the farming prescription. Knowing what information is available in Web Soil Survey provides a better understanding of the map unit, its components, and the component properties, and how they are impacting the crop productivity.

The answer to “Can Web Soil Survey Help to Uncover Answers to Precision Farming Questions?” is, “Yes”. The value in the WSS is not in the thematic maps but in the reports. The reports explain the minor soil components, where they occur, and their unique soil properties. In this example, the low productivity areas on a yield monitoring map is due to the eroded minor component with the high carbonates at the surface. That high carbonate content will bind the fertilizer. The prescription for the precision farmer who is targeting a 300-bushel irrigated corn yield in this field would be to:

  1. Set the planter to not plant in the eroded areas.
  2. Set the fertilizer unit to not fertilize these areas.
  3. Set the irrigation pivot to avoid irrigating these areas.

Removing the eroded areas from production will lower the input costs and increase the productivity to the targeted yield, and increase the harvest profits.

Precision farmers are targeting the planting, fertilizing, and irrigating to obtain the highest production with the lowest input cost. Removing unproductive areas from the prescription allows for a higher return with a lower input. The Web Soil Survey reports contain the information to help answer questions, however the user must dig deeper.

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[…] Soil survey tools (SoilWeb, Web Soil Survey, Google Earth Pro) are available to provide information beyond the usual soil fertility sampling. These survey tools help to provide an understanding in the soil morphology and how the morphology may impact yield productivity. Each tool was designed for a specific purpose and each tool was designed as a standalone product. The SoilWeb (University of California Davis/NRCS) was designed as a smartphone field application and contains a limited amount of the soil survey information. The Web Soil Survey (NRCS) was designed as a replacement to the historical soil survey manuscripts and contains access to the entire Soil Data Mart database. The SoilWeb provides a KML file for those who use Google Earth Pro. […]