Prairie Hills Soils Consulting
Interpreting soils information from the USDA Soils Database to meet customer's planning needs for urban and farming uses since 1980
Precision Farming - Can Web Soil Survey Help to Uncover Answers to Precision Farming Questions?
Gil Gullickson, crops technology writer for Successful Farming magazine, recently published an  article  where he interviewed two individuals discussing how the topography of a field can assist farmers in understanding soils. I encourage you to select the link and read the informative  article . In the article a paragraph began with "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.". Being a 37 year NRCS soils mapper I read that statement with some trepidation thinking that may be a proper historical perspective, however today's maps and the database have evolved from hard copy soils maps to digital maps and data.

The article continued: "“We are lucky to have had NRCS maps and understand them as we have,” says Bruce Erickson, Purdue University education distance and outreach director. “But in precision farming, we are ready to go to the next step.”". The soils maps NRCS/SCS originally created were designed for 'broad land use planning', but in recent years has been improving the product, maybe not for precision farming, but to add more valuable information. The paragraph went on to state: "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, says Erickson.". That is when I realized that the statements Gil heard from the speakers told me more information was needed to expand upon the speaker's opinions. Some of my recent consultation with precision farming firms had shown me that many were not aware of the full breath and depth of the soils database.

Compare the soils map (below) to the crop yield image (above) and note the image signatures. The crop yield monitor has specific red areas designating lower production that correspond to the white areas in the image below. These areas of lower crop yields fall within a map unit. So, what can the 'soils map' tell us about the soils within the polygons?

Using Web Soil Survey, we can identify three map units that exist on the farm.

Precision farming uses many inputs to develop a prescription for farming. The soils map, the crop yield monitoring map, maybe  Veris (Salina KS company)   EC mapping (David Little article) , drone imagery for crop scouting, elevation analysis, and even soil moisture monitoring can all be used for prescriptive analysis. But, it all starts with the soil. And the value of the soil map is to make informed decisions understanding the soil properties that impact these various inputs. Using these various input maps it is obvious there are multiple soil components within the map unit. Unfortunately, most soil map users consider there is only one soil component because of the polygon lines or they only look at the first soil component in the map unit. What users fail to recognize is there are a number of components in the map unit. Consider map unit '10' in the field above. This 'soil map unit' has 5 soil components noted in the database. However, most users consider only the first 'Colby' soil when planning. Note the variety of components and their cover kinds, slopes, and erosion classes:

Although the Colby component makes up the majority of the map unit (95%), note there is an eroded 20% component of the Colby soil appearing in this map unit (white areas on the image). Each of these 5 components have their own unique set of soil properties and the Colby component has the eroded phase separated in order to properly define its unique set of properties. Note the horizonation and soil properties for the non-eroded Colby component:

Contrast the soil properties to the eroded Colby component recognized in the same map unit. Notice the erosion of the surface horizon exposes the high carbonate loess materials containing lower organic matter and higher carbonate contents, both affecting productivity of the crop. Note the horizonation of this young non-eroded Colby soil (75%) to the eroded Colby (20%) and how both being formed in loess and have very little soil development.

“There is a strong correlation,” says Austin Bontrager, a Servi-Tech agronomy technology support specialist. “Within a field, you might see a general trend between soil type boundaries and actual field topography, but it will not line up perfectly.” Most soils map users consider there is only one instance of a soil component recognized in the map unit polygon. However the soil mapper tries to identify the minor components and its location as it occurs within the map unit. In the map unit '10' 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. By running a WSS report, the user can identify the components and their locations within the polygon boundaries.

“You can extract lots of information from maps like these,” says Erickson. “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.” Erickson's true statement eluded to the use of 'functional maps' and algorithms to identify topological components on the landscape. Going one step further and using the Soil Data Mart database reports allows the user to confirm the soils and its properties that aid in the prescription of the field and better understanding the soil properties that are impacting the crop productivity.

So the question 'Can Web Soil Survey Help to Uncover Answers to Precision Farming Questions?' has the answer 'Yes'. The value in the WSS is not only in the thematic maps, but also in the reports. The reports provide the user information to uncover the minor soil components, where they occur, and their specific properties. In this example, the low productivity is due to the eroded minor component with the high carbonates brought to the surface. That high carbonate content will bind the fertilizers which helps to explain the lower productivity. The prescription for the precision farmer who is targeting a 300 bushel irrigated corn yield is 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.

Precision farmers are targeting planting, fertilizing, and irrigating to get the highest production with the lowest input cost. Removing unproductive areas from the prescription allows for a higher return and a lower input. The soil survey contains the information to help answer the questions, you just have to dig deeper.

For more information on how the NRCS soils database can be utilized to make decisions, contact Paul R. Finnell, Sr, owner of Prairie Hills Soils Consulting at [email protected]